INBR 7 - Neuroanatomy Flashcards

Question

25. Memasok pedunkel serebelar tengah.

Answer 1

(C) The vertebral artery (VA) is generally the l argest branch of the subclavian artery; as a variant, the left VA arises from the aortic arch about 4% of the time. There are four segments of the vertebral artery (E). The first courses superiorly and posteriorly to enter the transverse foramen of the sixth cer\'ical vertebral body. The second segment ascends vertically within the transverse foramina, accompanied by a network of sympathetic fibers from the stellate ganglion and a venous plexus. I t turns laterally within the transverse process of the axis. The third segment exits the foramen of the axis and curves posteriorly and medially in a groove on the upper surface of the atlas to enter the foramen magnum. The fourth and last segment pierces the dura and joins the opposite VA near the lower pontine border. Branches of the V-A include the anterior meningeal artery, which may occasionally feed meningiomas or clival chordomas; the posterior meningeal arfery; posterior spinal artery; posterior inferior cerebellar artery (PICA) (D), and the anterior spinal artery. Occlusion of PICA (D) or the vertebral artery (E) may produce the lateral medullary (Wallenberg) syndrome, which is characterized by ipsilateral facial numbness; contralateral trunk numbness; ipsilateral palatal, pharyngeal, and vocal cord paralysis (nucleus ambiguus ) ; ipsilateral Horner's syndrome; vertigo; nausea; vomiting; ipsilateral cerebellar signs; and occasionally hiccups. The most common cause of Wallenberg syndrome is VA occlusion ; however, it has classically been described in the literature after PICA occlusion. The PICA vessels are at risk for injury during a Chiari decompression, as they loop around the tonsils. The characteristic picture of anterior inferior cerebellar artery (AICA) (C)' occlusion includes vertigo, nystagmus, nausea and vomiting (vestibular nuclei involvement), ipsilateral facial numbness (trigeminal spinal nucleus and 'tract), ipsilateral Horner's syndrome (descending sympathetic fibers), contralateral limb numbness (lateral spinothalamic tract), ipsilateral ataxia (middle cerebellar peduncle) , and ipsilateral deafness and facial paralysis (lateral pontomedullary tegmentum). It supplies the middle and inferior lateral pontine regions and the anterolateral parts of the cerebellum, which includes the middle cerebellar peduncle, flocculus, pyramis, and tuber. It is the most common vessel compressing the seventh cranial nerve during hemifacial spasm, which occasionally requires surgical decompression. Occlusion of the SCA (B) is the least common cause of cerebellar infarction, which is characterized by nausea, vomiting, vertigo, nystagmus, ipsilateral Horner's syndrome, ataxia, ipsilateral intention tremor (superior cerebellar peduncle), contralateral limb numbness, contralateral hearing loss (crossed fibers of the lateral lemniscus), and possibly a fourth nerve palsy (pontine tectum) . The SCA is the most common nerve compressing the trigeminal nerve i n trigeminal neuralgia. The posterior cerebral arteries (A) are joined by the posterior communicating arteries (PComA) about 1 em from their origin . The PComA is the major origin of the PCA 15 to 20% of the time and is termed a "fetal" PCA. The PCA comprises the P1 (peduncular), P2 (ambient) , P3 (quadrigeminal) , and P4 (distal or cortical) segments and their respective branches . Major branches of the PCA include the medial and lateral posterior choroidal arteries; anterior, middle, and posterior temporal arteries; parieto-occipital artery; calcarine artery; as well as the smaller thalamoperforating and thalamogeniculate arteries. The origin of the PComA is the first or second most common location for aneurysm formation, along with the anterior communicating artery ( Brazis, p p . 37 4-3 7 7 ; Kaye and Black, pp. 1603, 1734; Osborn DCA, p p . 153-193; Greenberg, pp. 107-108) .

Answer 2

(C) Afferent connections into the hypothalamus are umerous and complex. Seven of the main pathways are described below. 1. Amygdalohypothalamic fibers pass from the amygdala to the hypothalamus by two pathways: the stria terminalis and a pathway under the lentiform nucleus (ventral amygdalofugal fibers). The stria terminalis arises mainly from the corticomedial part of the amygdala and distributes fibers to the medial preoptic nucleus, anterior hypothalamic nucleus , and ventromedial and arcuate nuclei. Ventral amygdalofugal fibers arise from the basolateral amygdala and pyriform cortex and spread medially and rostrally under the lentiform nucleus to reach the lateral hypothalamus and medial forebrain bundle. 2. Visceral and somatic fibers reach the hypothalamus through collateral branches of the lemniscal tracts and reticular formation. 3. Basal olfactory, septal nuclei, periamygdaloid, and subiculum fibers reach the lateral and preoptic hypothalamic regions via the medial forebrain bundle . 4. Cortical fibers to the hypothalamus arise mainly from the frontal lobe. 5. Hippocampohypothalamic fibers travel through the fornix to the mammillary body. 6. Thalamohypothalamic fibers arise from the dorsomedial and midline thalamic nuclei. 7. Brainstem fibers to the hypothalamus arise from the raphe nuclei of the midbrain, the lateral parabrachial nuclei of the pons, and the locus ceruleus. Brainstem reticular fibers also ascend to the hypothalamus by the mammillary pedicle and dorsal longitudinal fasciculus (Carpenter, pp. 304-307 ; Kandel, pp. 972-981 , 992-993 ) .

Answer 3

(A) The cerebellar glomeruli have synaptic connections consisting of mossy fiber rosettes, axons of Golgi type II neurons, and dendrites of granule cells. A glial capsule surrounds this conglomeration. The axons of the granule neurons, which enter the molecular layer, provide the output from the glomerulus. Climbing fibers bypass the glomeruli to synapse directly on Purkinje cells (Carpenter, pp. 224-234). 2 8 .

Answer 4

(B) The major site of neuroblast proliferation in the CNS is the periventricular ependymal surface. After undergoing mitosis, these young neural cells migrate away from the ependyma ( El liso n , p. 7 1 ) .

Answer 5

(D) The cerebellar cortex consists of a molecular layer, Purkinje cell layer, and granular layer. The granular layer is deepest and lies just above the central medullary white matter. This layer contains the granule cells, which utilize glutamate as their neurotransmitter and are the only excitatory cells of the cerebellar cortex. Granule cell dendrites terminate in glomeruli, and their axons ascend to the molecular layer of the cerebellum as parallel fibers, which synapse with Purkinje cell dendrites. Golgi type II cells also reside in the granular layer of the cerebellar cortex. These cells are inhibitory (GABA) interneurons; their dendrites contact parallel fibers while their axons terminate in glomeruli. Each glomerulus consists of granule cell dendrites, Golgi cell axons , and a mossy fiber rosette. The Purkinje cells reside in the middle layer of the cerebellar cortex; they are large cells that project inhibitory fibers (GABA) to the deep cerebellar nuclei and the vestibular nuclei. The Purkinje cell represents the only output of the cerebellar cortex, which is inhibitory. Purkinje cells have extensive dendritic arborizations that extend into the molecular layer and are stimulated by parallel fibers and climbing fibers. Specialized astrocytes, called Bergman cells (Golgi epithelial cells) , surround Purkinje cells within the Purkinje cell layer and provide supportive functions. The molecular layer is the most superficial layer of the cerebellar cortex; it contains stellate cells, basket cell . Purkinje dendrites, and pqrallel fibers (from granule cells). Stellate cells make synaptic contacts with Purkinje cell dendrites, while basket cells form synapses on Purkinje cell bodies. Both stellate and basket cells are inhibitory and utilize GABA as their neurotransmitter. Cerebellar cortical input occurs via climbing fibers an • mossy fibers. Climbing fibers originate in the inferior oli,•e (olivocerebellars) ; they ascend to the molecular layer. "'•h;:re they directly stimulate the dendrites of small numb rs u

Answer 6

(C) The annulus tendineus (of Zinn) lies at the apes the periorbita and gives rise to four rectus muscles. The o

Answer 7

(K) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 8

(A) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 9

(I) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 10

(J) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 11

(G) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 12

(H) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 13

(H) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 14

(F) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 15

(H) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 16

(F) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 17

(E) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 18

(I) The brachial plexus is formed from the anterior primary rami of segments CS, C6, C7, C8, and T l . It is about 15 em long in adults and e,xtends from the spinal cord to the axilla. It is divided into five major components, as follows : roots, trunks, divisions, cords, and branches. The fifth and sixth cervical roots unite to form the upper trunk of the plexus, and the eighth cervical and first thoracic spinal roots unite to form the lower trunk. The seventh cervical root emerges as the middle trunk of the plexus. The three trunks then traverse the supraclavicular fossa, behind the axillary artery, and .s.e.parate into three anterior and three posterior divi

Answer 19

(C) The cells of the cerebral cortex show both a laminar and radial or columnar arrangement. Several areas of cortex have grossly visible stripes of myelinated fibers, most notably the band of Gennari in layer IV of the occipital cortex. Most cytoarchitectural boundaries are vague rather than sharp. The large pyramidal neurons located in layer V of the visual receptive cortex send axons to the brainstem that mediate visually directed ret1ex eye movements (Carpenter, pp. 390- 433 ) .

Answer 20

(B) The arcuate fasciculus projects from the superior temporal gyrus (STG) to the superior and middle frontal gyri. More commonly, it is known as the tract that links the receptive area of speech in the superior temporal gyrus (Wernicke's area) with the inferior frontal gyrus (Broca's area) . Lesions in this tract often produce conduction aphasia, in which patients have t1uent speech with poor repetition of spoken language. \Vernicke's aphasia (WA) is a receptive aphasia characterized by poor comprehension of spoken language, neologisms, literal and verbal paraphasias, poor repetition, and a lack of concern regarding the speech problem. Injury to Broca's area results in an executive aphasia characterized by slow and effortful speech, agrammatic sounds, and telegraphic speech. The uncinate fasciculus connects the orbital frontal gyri with the anterior portions of the temporal lobe, while the cingulum connects the medial regions of the frontal and parietal lobes with the parahippocampal and temporal regions. The fibers of the superior and inferior longitudinal fasciculus lie close to the arcuate fasciculus and connect the parietal and occipital lobes with the frontal and temporal lobes, respectively. The anterior commissure (association tract) crosses the midline rostral to the fornix and has two parts: the smaller anterior portion interconnects the olfactory bulbs, and the larger posterior portion interconnects the middle and inferior temporal gyri (Carpenter, pp. 33-3 7 ) .

Answer 21

(E) The combination o f pupillary constriction and ptosis suggests a Horner's syndrome. Two muscles ele\'ate the eyelid: the levator palpebrae (CN III) and the superior tarsal muscle of •Muller (carotid sympathetic nerve). The key to further differentiation is the size of the pupil. A lesion of cranial .nerve I I I may likely result in pupillodilation (due to pupilloconstrictor muscle paralysis), whereas injury to the sympathetic nerve would result in pupil constriction , as seen in this patient. In addition, the ptosis of sympathetic paralysis may improve when the patient volitionally looks up , because the levator palpebrae is the muscle that mediates voluntary upward gaze. The lesion causing injury to the sym- CHAPTER 2 Neuroanatomy Answers 41 pathetics may originate i n any location along the descending pathways from the hypothalamus through the spinal cord and out through the peripheral pathways along the sympathetic chain and carotid artery (see discussion for question 6) (Brazis, pp. 181-182; Greenberg, p. 578).

Answer 22

(B) The striate cortex is organized in both vertical and horizontal systems. The vertical or columnar system is mainly concerned with line orientation, retinal position, detection of movements, and ocular dominance. Ihe two regions of the striate cortex that do not contain ocular dominance columns include the region representing the blind spot of the eye and the cortical regimi representing the monocular temporal crescent of the visual fields (Carpenter, pp. 411-414) .

Answer 23

(D) The first clinically relevant branch of the lumbar plexus is the lateral femoral cutaneous nerve of the thigh (A, L2-3), which reaches the thigh by passing under the lateral aspect of the inguinal ligament. Entrapment of this nerve as it enters the thigh can produce a numb, tingling, or burning hypersensitivity over the lateral thigh known as meralgia paresthetica. It is often encountered in obese patients of either sex who have lost a significant amount of weight, or, conversely, can be seen in late pregnancy due to a sagging anterior abdominal wall. This condition often remits on its own, but surgical decompression is sometimes warranted. The femoral nerve (B, E, L2-4) passes down along the lateral aspect of the psoas muscle and emerges under the inguinal ligament into the femoral triangle. It innervates the iliopsoas (hip t1exion), sartorius (hip t1exion, thigh eversion), and quadriceps femoris muscles (knee extension). I n the abdomen and pelvis, a primary or secondary neoplasm, psoas abscess, or pelvic hematoma may damage the upper portion of this nerve (B). In the femoral ring (E), this nerve is particularly vulnerable to local compression and possibly pressure palsy from diabetes mellitus. Although diabetes can also affect the L2-4 roots of this nerve, diabetic neuropathy of the femoral nerve is most often encountered in the femoral triangle. The patient usually presents with pain that resolves, only to be followed by rapid wasting and weakness of the quadriceps, which makes walking very difficult. Fortunately, the condition eventually improves, although it may take up to 2 years. The obturator nerve (D, L2-4) lies, on the medial side of the iliopsoas muscle and comes into close relationship with the uterus before reaching the obturator foramen. In the pelvis, it is particularly vulnerable to injury during obstetric and gynecologic procedt1res. This nerve supplies the adductor muscles of the thigh, which includes the pectineus; adductor longus, brevis, and magnus; and gracili.t; muscles. I ts integrity is tested by having the patient hold the legs together against resistance. The sciatic nerve (C, F) consists of two discrete components invested by the same fascia called the peroneal and 42 Intensive Neurosurgery Board Review tibial nerves. This major nerve may also be damaged in the pelvis by direct spread of neoplasms (along with the femoral nerve), particularly from the rectum or genitourinary tract. In the buttock, misplaced deep intramuscular injections, complicated hip ' fractures, and penetrating trauma are the most frequent causes of sciatic nerve damage. Misplaced injections can be especially problematic, because they can produce not only significant weakness but also severe causalgic pain over the leg and foot that is often refractory to medications. The superior gluteal neurovascular bundle lies in the superomedial gluteal quadrant. The sciatic nerve and inferior gluteal neurovascular bundle lie in the inferolateral and inferomedial quadrants, respectively. The safest location for intramuscular injection is the superolateral gluteal quadrant. The peroneal nerve is particularly vulnerable to injury as it crosses near the fibular neck, although this nerve is more resilient to injury than the tibial nerve after sciatic nerve injury. The reason for this is not entirely clear ( Patten, pp. 299-310; Brazis, pp. 62-65, 73-7 7; April , p. 584).

Answer 24

(A) The first clinically relevant branch of the lumbar plexus is the lateral femoral cutaneous nerve of the thigh (A, L2-3), which reaches the thigh by passing under the lateral aspect of the inguinal ligament. Entrapment of this nerve as it enters the thigh can produce a numb, tingling, or burning hypersensitivity over the lateral thigh known as meralgia paresthetica. It is often encountered in obese patients of either sex who have lost a significant amount of weight, or, conversely, can be seen in late pregnancy due to a sagging anterior abdominal wall. This condition often remits on its own, but surgical decompression is sometimes warranted. The femoral nerve (B, E, L2-4) passes down along the lateral aspect of the psoas muscle and emerges under the inguinal ligament into the femoral triangle. It innervates the iliopsoas (hip t1exion), sartorius (hip t1exion, thigh eversion), and quadriceps femoris muscles (knee extension). I n the abdomen and pelvis, a primary or secondary neoplasm, psoas abscess, or pelvic hematoma may damage the upper portion of this nerve (B). In the femoral ring (E), this nerve is particularly vulnerable to local compression and possibly pressure palsy from diabetes mellitus. Although diabetes can also affect the L2-4 roots of this nerve, diabetic neuropathy of the femoral nerve is most often encountered in the femoral triangle. The patient usually presents with pain that resolves, only to be followed by rapid wasting and weakness of the quadriceps, which makes walking very difficult. Fortunately, the condition eventually improves, although it may take up to 2 years. The obturator nerve (D, L2-4) lies, on the medial side of the iliopsoas muscle and comes into close relationship with the uterus before reaching the obturator foramen. In the pelvis, it is particularly vulnerable to injury during obstetric and gynecologic procedt1res. This nerve supplies the adductor muscles of the thigh, which includes the pectineus; adductor longus, brevis, and magnus; and gracili.t; muscles. I ts integrity is tested by having the patient hold the legs together against resistance. The sciatic nerve (C, F) consists of two discrete components invested by the same fascia called the peroneal and 42 Intensive Neurosurgery Board Review tibial nerves. This major nerve may also be damaged in the pelvis by direct spread of neoplasms (along with the femoral nerve), particularly from the rectum or genitourinary tract. In the buttock, misplaced deep intramuscular injections, complicated hip ' fractures, and penetrating trauma are the most frequent causes of sciatic nerve damage. Misplaced injections can be especially problematic, because they can produce not only significant weakness but also severe causalgic pain over the leg and foot that is often refractory to medications. The superior gluteal neurovascular bundle lies in the superomedial gluteal quadrant. The sciatic nerve and inferior gluteal neurovascular bundle lie in the inferolateral and inferomedial quadrants, respectively. The safest location for intramuscular injection is the superolateral gluteal quadrant. The peroneal nerve is particularly vulnerable to injury as it crosses near the fibular neck, although this nerve is more resilient to injury than the tibial nerve after sciatic nerve injury. The reason for this is not entirely clear ( Patten, pp. 299-310; Brazis, pp. 62-65, 73-7 7; April , p. 584).

Answer 25

(B) The first clinically relevant branch of the lumbar plexus is the lateral femoral cutaneous nerve of the thigh (A, L2-3), which reaches the thigh by passing under the lateral aspect of the inguinal ligament. Entrapment of this nerve as it enters the thigh can produce a numb, tingling, or burning hypersensitivity over the lateral thigh known as meralgia paresthetica. It is often encountered in obese patients of either sex who have lost a significant amount of weight, or, conversely, can be seen in late pregnancy due to a sagging anterior abdominal wall. This condition often remits on its own, but surgical decompression is sometimes warranted. The femoral nerve (B, E, L2-4) passes down along the lateral aspect of the psoas muscle and emerges under the inguinal ligament into the femoral triangle. It innervates the iliopsoas (hip t1exion), sartorius (hip t1exion, thigh eversion), and quadriceps femoris muscles (knee extension). I n the abdomen and pelvis, a primary or secondary neoplasm, psoas abscess, or pelvic hematoma may damage the upper portion of this nerve (B). In the femoral ring (E), this nerve is particularly vulnerable to local compression and possibly pressure palsy from diabetes mellitus. Although diabetes can also affect the L2-4 roots of this nerve, diabetic neuropathy of the femoral nerve is most often encountered in the femoral triangle. The patient usually presents with pain that resolves, only to be followed by rapid wasting and weakness of the quadriceps, which makes walking very difficult. Fortunately, the condition eventually improves, although it may take up to 2 years. The obturator nerve (D, L2-4) lies, on the medial side of the iliopsoas muscle and comes into close relationship with the uterus before reaching the obturator foramen. In the pelvis, it is particularly vulnerable to injury during obstetric and gynecologic procedt1res. This nerve supplies the adductor muscles of the thigh, which includes the pectineus; adductor longus, brevis, and magnus; and gracili.t; muscles. I ts integrity is tested by having the patient hold the legs together against resistance. The sciatic nerve (C, F) consists of two discrete components invested by the same fascia called the peroneal and 42 Intensive Neurosurgery Board Review tibial nerves. This major nerve may also be damaged in the pelvis by direct spread of neoplasms (along with the femoral nerve), particularly from the rectum or genitourinary tract. In the buttock, misplaced deep intramuscular injections, complicated hip ' fractures, and penetrating trauma are the most frequent causes of sciatic nerve damage. Misplaced injections can be especially problematic, because they can produce not only significant weakness but also severe causalgic pain over the leg and foot that is often refractory to medications. The superior gluteal neurovascular bundle lies in the superomedial gluteal quadrant. The sciatic nerve and inferior gluteal neurovascular bundle lie in the inferolateral and inferomedial quadrants, respectively. The safest location for intramuscular injection is the superolateral gluteal quadrant. The peroneal nerve is particularly vulnerable to injury as it crosses near the fibular neck, although this nerve is more resilient to injury than the tibial nerve after sciatic nerve injury. The reason for this is not entirely clear ( Patten, pp. 299-310; Brazis, pp. 62-65, 73-7 7; April , p. 584).

Answer 26

(E) The first clinically relevant branch of the lumbar plexus is the lateral femoral cutaneous nerve of the thigh (A, L2-3), which reaches the thigh by passing under the lateral aspect of the inguinal ligament. Entrapment of this nerve as it enters the thigh can produce a numb, tingling, or burning hypersensitivity over the lateral thigh known as meralgia paresthetica. It is often encountered in obese patients of either sex who have lost a significant amount of weight, or, conversely, can be seen in late pregnancy due to a sagging anterior abdominal wall. This condition often remits on its own, but surgical decompression is sometimes warranted. The femoral nerve (B, E, L2-4) passes down along the lateral aspect of the psoas muscle and emerges under the inguinal ligament into the femoral triangle. It innervates the iliopsoas (hip t1exion), sartorius (hip t1exion, thigh eversion), and quadriceps femoris muscles (knee extension). I n the abdomen and pelvis, a primary or secondary neoplasm, psoas abscess, or pelvic hematoma may damage the upper portion of this nerve (B). In the femoral ring (E), this nerve is particularly vulnerable to local compression and possibly pressure palsy from diabetes mellitus. Although diabetes can also affect the L2-4 roots of this nerve, diabetic neuropathy of the femoral nerve is most often encountered in the femoral triangle. The patient usually presents with pain that resolves, only to be followed by rapid wasting and weakness of the quadriceps, which makes walking very difficult. Fortunately, the condition eventually improves, although it may take up to 2 years. The obturator nerve (D, L2-4) lies, on the medial side of the iliopsoas muscle and comes into close relationship with the uterus before reaching the obturator foramen. In the pelvis, it is particularly vulnerable to injury during obstetric and gynecologic procedt1res. This nerve supplies the adductor muscles of the thigh, which includes the pectineus; adductor longus, brevis, and magnus; and gracili.t; muscles. I ts integrity is tested by having the patient hold the legs together against resistance. The sciatic nerve (C, F) consists of two discrete components invested by the same fascia called the peroneal and 42 Intensive Neurosurgery Board Review tibial nerves. This major nerve may also be damaged in the pelvis by direct spread of neoplasms (along with the femoral nerve), particularly from the rectum or genitourinary tract. In the buttock, misplaced deep intramuscular injections, complicated hip ' fractures, and penetrating trauma are the most frequent causes of sciatic nerve damage. Misplaced injections can be especially problematic, because they can produce not only significant weakness but also severe causalgic pain over the leg and foot that is often refractory to medications. The superior gluteal neurovascular bundle lies in the superomedial gluteal quadrant. The sciatic nerve and inferior gluteal neurovascular bundle lie in the inferolateral and inferomedial quadrants, respectively. The safest location for intramuscular injection is the superolateral gluteal quadrant. The peroneal nerve is particularly vulnerable to injury as it crosses near the fibular neck, although this nerve is more resilient to injury than the tibial nerve after sciatic nerve injury. The reason for this is not entirely clear ( Patten, pp. 299-310; Brazis, pp. 62-65, 73-7 7; April , p. 584).

Answer 27

(D) The first clinically relevant branch of the lumbar plexus is the lateral femoral cutaneous nerve of the thigh (A, L2-3), which reaches the thigh by passing under the lateral aspect of the inguinal ligament. Entrapment of this nerve as it enters the thigh can produce a numb, tingling, or burning hypersensitivity over the lateral thigh known as meralgia paresthetica. It is often encountered in obese patients of either sex who have lost a significant amount of weight, or, conversely, can be seen in late pregnancy due to a sagging anterior abdominal wall. This condition often remits on its own, but surgical decompression is sometimes warranted. The femoral nerve (B, E, L2-4) passes down along the lateral aspect of the psoas muscle and emerges under the inguinal ligament into the femoral triangle. It innervates the iliopsoas (hip t1exion), sartorius (hip t1exion, thigh eversion), and quadriceps femoris muscles (knee extension). I n the abdomen and pelvis, a primary or secondary neoplasm, psoas abscess, or pelvic hematoma may damage the upper portion of this nerve (B). In the femoral ring (E), this nerve is particularly vulnerable to local compression and possibly pressure palsy from diabetes mellitus. Although diabetes can also affect the L2-4 roots of this nerve, diabetic neuropathy of the femoral nerve is most often encountered in the femoral triangle. The patient usually presents with pain that resolves, only to be followed by rapid wasting and weakness of the quadriceps, which makes walking very difficult. Fortunately, the condition eventually improves, although it may take up to 2 years. The obturator nerve (D, L2-4) lies, on the medial side of the iliopsoas muscle and comes into close relationship with the uterus before reaching the obturator foramen. In the pelvis, it is particularly vulnerable to injury during obstetric and gynecologic procedt1res. This nerve supplies the adductor muscles of the thigh, which includes the pectineus; adductor longus, brevis, and magnus; and gracili.t; muscles. I ts integrity is tested by having the patient hold the legs together against resistance. The sciatic nerve (C, F) consists of two discrete components invested by the same fascia called the peroneal and 42 Intensive Neurosurgery Board Review tibial nerves. This major nerve may also be damaged in the pelvis by direct spread of neoplasms (along with the femoral nerve), particularly from the rectum or genitourinary tract. In the buttock, misplaced deep intramuscular injections, complicated hip ' fractures, and penetrating trauma are the most frequent causes of sciatic nerve damage. Misplaced injections can be especially problematic, because they can produce not only significant weakness but also severe causalgic pain over the leg and foot that is often refractory to medications. The superior gluteal neurovascular bundle lies in the superomedial gluteal quadrant. The sciatic nerve and inferior gluteal neurovascular bundle lie in the inferolateral and inferomedial quadrants, respectively. The safest location for intramuscular injection is the superolateral gluteal quadrant. The peroneal nerve is particularly vulnerable to injury as it crosses near the fibular neck, although this nerve is more resilient to injury than the tibial nerve after sciatic nerve injury. The reason for this is not entirely clear ( Patten, pp. 299-310; Brazis, pp. 62-65, 73-7 7; April , p. 584).

Answer 28

(E) Sympathetic preganglionic fibers originate from the T1 through L2 (thoracolumbar) levels of the spinal cord and pass successively through the ventral roots, anterior primary rami of the spinal nerves, and myelinated white rami communicans before synapsing in the sympathetic chain (composed of paravertebral ganglia and interconnecting fiber bundles) . Sympathetic postganglionic fibers from the paravertebral ganglia then may take one of several routes. They may pass back to a spinal nerve along an unmyelinated gray ramus communicans to innervate dermal sweat glands, smooth muscle cells of arterioles, and/or arrector pili muscles of the body and extremities. They may exit the sympathetic ganglia through splanchnic nerves to innervate the abdominal or pelvic viscera or may course up or down the sympathetic chain to synapse with postganglionic neurons located several spinal levels away. Every spinal nerve receives a gray ramus from the sympathetic chain, whereas only spinal levels T1-L2 have white rami communicans (myelinated). Preganglionic sympathetic neurons are cholinergic, whereas the sympathetic postganglionic fibers (some tra\'eling through gray ramus communicans) are adrenergic. Because the paravertebral and preVertebral ganglia are located some distance away from the organ innervated, the sympathetic preganglionic fibers are shorter, whereas postganglionic fibers are longer as compared to the parasympathetic division (Apri l , pp. 28-30).

Answer 29

(E) The superior ramus of the ansa cervicalis, which arises from C1 and the •hypoglossal nerve, innervates the geniohyoid (protracts hyoid) and thyrohyoid (raises larynx) muscles, whereas the inferior ramus, arising from C 1-C3, inner\'ates the omohyoid (lowers hyoid) and sternothyroid (lowers larynx) muscles. Since the muscles supplied by the ansa cervicalis often have collateral innervation, sectioning or mobilization of this structure during various surgical procedures (such as carotid endarterectomy) rarely has clinical consequences. The stylohyoid (elevates and retracts hyoid) muscle is innervated by CN VII (Apri l , p. 5 12).

Answer 30

(D) . The pterygopalatine fossa harbors many nerves and blood vessels, which directly communicate with various compartments of the face and skull. The pterygopalatine fossa communicates directly with the middle cranial fossa through the foramen rotundum and vidian canal, with the orbital cavity through the inferior orbital fissure, with the nasal cavity via the sphenopalatine foramen, and with the oral cavity by way of the palatine canal. It does not directly communicate with the inner ear (Apri l , pp. 490- 491).

Answer 31

(C) Adie's pupil (dilated pupil) is thought to be due to impaired postganglionic parasympathetics from a viral infection of the ciliary ganglion. Adie's pupil often constricts with dilute (0. 1 to 0. 1 25%) pilocarpine, a parasympathomimetic, because of denervation hypersensitivity (normal pupils react to 1% pilocarpine). The ArgyllRobertson pupils are believed to result from disruption of pathways leading to the Edinger-Westphal nucleus, which produces light-near dissociation (pupillary constriction with convergence and absent light response). The Marcus-Gunn pupil is best detected by the swinging flashlight test, as the consensual reflex is stronger than the direct reflex (afferent pupillary defect). It is caused by lesions anterior to the optic chiasm, such as retinal detachment or infarct, optic or retrobulbar neuritis, or trauma to the optic nerve. The presence of the consensual reflex is evidence of a preserved third nerve (with parasympathetics) on the side of the direct reflex. Horner's syndrome (HS) results from interruption of the sympathetic pupillomotor pathways anywhere between the primary motor neuron in the hypothalamus, the second motor neuron i n the cervicothoracic junction, and thirdorder neuron i n the superior cervical ganglion. Findings may include miosis, ptosis, enophthalmos, eye hyperemia, or anhidrosis of the face. Cocaine can be used if the diagnosis is i n doubt; however, this has no localizing value. Cocaine blocks norepinephrine (NE) reuptake by postganglionic sympathetic fibers at the neuroeffector junction. In HS, no NE is released, so cocaine cannot dilate the eye. If the pupil dilates normally, there is no HS. To differentiate a secondfrom a third-order neuron injury, administer 1% hydroxyamphetamine, which releases NE from nerve terminals at the neuroeffector junction. This causes pupillary dilation with second-order neuron lesions but not with third-order neuron damage (since third-order neurons do not release NE) (Greenberg, p. 578).

Answer 32

(B) Adie's pupil (dilated pupil) is thought to be due to impaired postganglionic parasympathetics from a viral infection of the ciliary ganglion. Adie's pupil often constricts with dilute (0. 1 to 0. 1 25%) pilocarpine, a parasympathomimetic, because of denervation hypersensitivity (normal pupils react to 1% pilocarpine). The ArgyllRobertson pupils are believed to result from disruption of pathways leading to the Edinger-Westphal nucleus, which produces light-near dissociation (pupillary constriction with convergence and absent light response). The Marcus-Gunn pupil is best detected by the swinging flashlight test, as the consensual reflex is stronger than the direct reflex (afferent pupillary defect). It is caused by lesions anterior to the optic chiasm, such as retinal detachment or infarct, optic or retrobulbar neuritis, or trauma to the optic nerve. The presence of the consensual reflex is evidence of a preserved third nerve (with parasympathetics) on the side of the direct reflex. Horner's syndrome (HS) results from interruption of the sympathetic pupillomotor pathways anywhere between the primary motor neuron in the hypothalamus, the second motor neuron i n the cervicothoracic junction, and thirdorder neuron i n the superior cervical ganglion. Findings may include miosis, ptosis, enophthalmos, eye hyperemia, or anhidrosis of the face. Cocaine can be used if the diagnosis is i n doubt; however, this has no localizing value. Cocaine blocks norepinephrine (NE) reuptake by postganglionic sympathetic fibers at the neuroeffector junction. In HS, no NE is released, so cocaine cannot dilate the eye. If the pupil dilates normally, there is no HS. To differentiate a secondfrom a third-order neuron injury, administer 1% hydroxyamphetamine, which releases NE from nerve terminals at the neuroeffector junction. This causes pupillary dilation with second-order neuron lesions but not with third-order neuron damage (since third-order neurons do not release NE) (Greenberg, p. 578).

Answer 33

(D) Adie's pupil (dilated pupil) is thought to be due to impaired postganglionic parasympathetics from a viral infection of the ciliary ganglion. Adie's pupil often constricts with dilute (0. 1 to 0. 1 25%) pilocarpine, a parasympathomimetic, because of denervation hypersensitivity (normal pupils react to 1% pilocarpine). The ArgyllRobertson pupils are believed to result from disruption of pathways leading to the Edinger-Westphal nucleus, which produces light-near dissociation (pupillary constriction with convergence and absent light response). The Marcus-Gunn pupil is best detected by the swinging flashlight test, as the consensual reflex is stronger than the direct reflex (afferent pupillary defect). It is caused by lesions anterior to the optic chiasm, such as retinal detachment or infarct, optic or retrobulbar neuritis, or trauma to the optic nerve. The presence of the consensual reflex is evidence of a preserved third nerve (with parasympathetics) on the side of the direct reflex. Horner's syndrome (HS) results from interruption of the sympathetic pupillomotor pathways anywhere between the primary motor neuron in the hypothalamus, the second motor neuron i n the cervicothoracic junction, and thirdorder neuron i n the superior cervical ganglion. Findings may include miosis, ptosis, enophthalmos, eye hyperemia, or anhidrosis of the face. Cocaine can be used if the diagnosis is i n doubt; however, this has no localizing value. Cocaine blocks norepinephrine (NE) reuptake by postganglionic sympathetic fibers at the neuroeffector junction. In HS, no NE is released, so cocaine cannot dilate the eye. If the pupil dilates normally, there is no HS. To differentiate a secondfrom a third-order neuron injury, administer 1% hydroxyamphetamine, which releases NE from nerve terminals at the neuroeffector junction. This causes pupillary dilation with second-order neuron lesions but not with third-order neuron damage (since third-order neurons do not release NE) (Greenberg, p. 578).

Answer 34

(A) Adie's pupil (dilated pupil) is thought to be due to impaired postganglionic parasympathetics from a viral infection of the ciliary ganglion. Adie's pupil often constricts with dilute (0. 1 to 0. 1 25%) pilocarpine, a parasympathomimetic, because of denervation hypersensitivity (normal pupils react to 1% pilocarpine). The ArgyllRobertson pupils are believed to result from disruption of pathways leading to the Edinger-Westphal nucleus, which produces light-near dissociation (pupillary constriction with convergence and absent light response). The Marcus-Gunn pupil is best detected by the swinging flashlight test, as the consensual reflex is stronger than the direct reflex (afferent pupillary defect). It is caused by lesions anterior to the optic chiasm, such as retinal detachment or infarct, optic or retrobulbar neuritis, or trauma to the optic nerve. The presence of the consensual reflex is evidence of a preserved third nerve (with parasympathetics) on the side of the direct reflex. Horner's syndrome (HS) results from interruption of the sympathetic pupillomotor pathways anywhere between the primary motor neuron in the hypothalamus, the second motor neuron i n the cervicothoracic junction, and thirdorder neuron i n the superior cervical ganglion. Findings may include miosis, ptosis, enophthalmos, eye hyperemia, or anhidrosis of the face. Cocaine can be used if the diagnosis is i n doubt; however, this has no localizing value. Cocaine blocks norepinephrine (NE) reuptake by postganglionic sympathetic fibers at the neuroeffector junction. In HS, no NE is released, so cocaine cannot dilate the eye. If the pupil dilates normally, there is no HS. To differentiate a secondfrom a third-order neuron injury, administer 1% hydroxyamphetamine, which releases NE from nerve terminals at the neuroeffector junction. This causes pupillary dilation with second-order neuron lesions but not with third-order neuron damage (since third-order neurons do not release NE) (Greenberg, p. 578).

Answer 35

C. The term corpus striatum refers to the caudate, putamen, and pallidum, whereas the term striatum typically includes only the caudate nucleus and putamen. The lentiform nuclei consist of the globus pallidus and putamen, which lie between the internal and extreme capsules and are separated by a curved vertical lamina of white matter called the lateral medullary lamina. Other terms commonly used to refer to the basal ganglia include neostriatum (caudate nucleus and putamen), paleostriatum (globus pallidus), and archistriatum (amygdaloid complex). All the structures mentioned above except for the globus pallid us (and subthalamic nucleus) are believed to have originated from the telencephalon, which is a diencephalic structure (Carpenter, p. 325).

Answer 36

C. The largest number of afferent fibers into the STN originate in the lateral pallidal segment. Afferents to the STN from the motor, premotor, and prefrontal cortex are mainly collaterals from other tracts, while a relatively small number of afferents originate from the Clvl nucleus of the thalamus. Mferents to the STN from the lateral pallidal segment are mainly GABAergic, while most cells of the STN are believed to release glutamate and exert excitatory effects on their targets. The medial globus pallidus is the major outflow site of the basal ganglia, as described in the discussion for question 2 (Carpenter, pp. 347-351) .

Answer 37

E. The corticopontocerebellar tract consists almost entirely of crossed fibers from the pontine nuclei that transmit impulses from the cerebral cortex to the intermediate and lateral zones of the cerebellum through the middle cerebellar peduncle (brachium pontis). The inferior cerebellar peduncle connects the medulla to the cerebellum and consists of two divisions: the restiform body contains afferent fibers from the olivocerebellar, dorsal spinocerebellar, reticulocerebellar, and cuneocerebellar tracts, while the juxtarestiform body contains both afferent (vestibulocerebellar) and efferent ( cerebellovestibular) fibers. The superior cerebellar peduncle (brachium conjuctivum) consists principally of efferents from the cerebellum. Rubral , thalamic, and reticular projections arise from the dentate and interposed nuclei, which exit the cerebellum via the superior cerebellar peduncle. Mferent tracts into the superior cerebellar peduncle include the ventral spinocerebellar, trigeminocerebellar, and tectocerebellar tracts ( Kandel, pp. 626-646; Fix, pp. 196-197 ) .

Answer 38

(C) T h e following layers are distinguished in the neocortex in passing from the pial surface toward the white matter: Layer I (molecular layer): contains cells with horizontal axons and Golgi type II cells. Layer II (external granular layer): consists mostly of closely packed granule cells. Layer I I I (external pyramidal layer) : consists of two sublayers of pyramidal neurons. Layer IV (internal granular layer) : comprises closely packed stellate cells with either short aJwns ramifying within the layer or larger axons projecting to deeper layers. Myelinated fibers of the external band of Baillarger form a prominem horizontal plexus in this layer. Layer V (internal pyramidal layer) : consists mainly of medium and large pyramidal cells (Betz cells). Apical dendrites of large pyramidal cells project to the molecular layer. while axons mainly leave the cortex as projection fibers. Layer VI (multiform layer): contains spindle-shaped cells whose long axes are perpendicular to the cortical suriace

Answer 39

D. Some areas o f the body have a greater sensori representation than others. -The largest areas in, tongue, thumb, little finger, and corresponding digirs or foot, as well as the hands and feet in general. The complexi - of motor actions of the thumb requires a larger circuitry than the trunk, index finger, nipple, geniralia middle finger (Carpenter, p p . 401-404). I 44 Intensive Neurosurgery Board Review

Answer 40

C. Both the archicortex and neocortex are laminated, contain pyramidal neurons, and have connections with the limbic system. One major difference is that the archicortex has a distinct sup

Answer 41

C. The nuclei of the hypothalamus are divided by an imaginary plane formed by the columns of the fornix and mammillothalamic tract into medial and lateral groups. The medial hypothalamic area is again divided into four regions from anterior to posterior: preoptic, supraoptic, tuberal, and mammillary regions. Each of these regions contains a separate subgroup of nuclei . Medial group 1. Preoptic region: contains the medial preoptic nucleus involved with the release of gonadotropic hormones. This nucleus is sexually dimorphic and requires testosterone for development. 2. Supraoptic region: contains the supraoptic nucleus (synthesizes ADH and oxytocin), paraventricular nucleus (makes and releases ADH, oxytocin, and CRH) , anterior nucleus (plays a role in temperature regulation) , and suprachiasmatic nucleus (controls circadian rhythms), which lie dorsal to the optic chiasm. 3 . Tuberal region: the arcuate nucleus is located in the tuber cinereum; it contains neurons that produce hypothalamic releasing factors and gives rise to the tuberohypophysial tract, which terminates in the hypophyseal portal system of the infundibulum. This nucleus regulates the release of adenohypophyseal hormones into the systemic circulation. The arcuate nucleus, along with the dorsomedial and ventromedial nuclei, lies dorsal to the tuber cinereum and makes up the nuclei adjacent to this structure. 4. Mammillary region: this contains the mammillary and posterior nuclei, which lie dorsal to the mammillary bodies. The lateral hypothalamic area is traversed by the medial forebrain bundle and includes two major nuclei: the lateral preoptic and lateral hypothalamic nuclei (Carpenter, pp. 297-303).

Answer 42

E. The supraoptic and paraventricular nuclei of the hypothalamus synthesize and secrete vasopressin and oxytocin, respectively. The anterior portion of the hypothalamus controls mechanisms that dissipate heat. Stimulation of this area causes dilaticm of blood vessels and sweating, which lowers body temperature. Stimulation of the posterior hypothalamus results in vasoconstriction of blood vessels, inhibition of sweating, and possibly shivering, which may increase body temperature. The posterior (mainly) and lateral hypothalamic nuclei are also involved with the sympathetic nervous system control. The lateral region of the hypothalamus is sometimes referred to as either the hunger and thirst center, as stimulation can result in increased food and water intake. Stimulation of the medial region of the hypothalamus results in decreased food intake; it is often referred to as the satiety center. The suprachiasmatic nucleus controls circadian rhythms, and the anterior and preoptic nuclei help to control parasympathetic responses as well as gonadotropin secretion (Carpenter, pp. 3 1 7 -324).

Answer 43

A. The sciatic nerve (L4-S3) is the major branch of the sacral plexus and is also the largest nerve in the body. The sciatic nerve consists of the tibial and common peroneal nerves. The tibial nerve (L4-S3) innervates the flexors of the leg, including the semitendinosus, semimembranosus, biceps femoris, gastrocnemius, soleus, flexor hallucis longus, flexor digitorum longus, popliteus, tibialis posterior, and plantaris. The tibial nerve gives rise to the lateral sural cutaneous nerve, which unites with the communicating branch of the peroneal nerve to form the sural nerve. This nerve supplies cutaneous innervation to the lateral inferior leg and lateral foot. The tibial nerve may become entrapped in the tarsal tunnel posterior and inferior to the medial malleolus, which results in pain and paresthesias in the toes and sole of the foot (often sparing the heel because these sensory branches often originate proximal to the tarsal tunnel) and wealmess on plantarflexion . The common peroneal nerve (L4-S2) innervates extensors and adductors of the leg (and part of the biceps femoris) and gives rise to the lateral sural cutaneous nerve (to the inferolateral leg), the deep peroneal nerve, and the superficial peroneal nerve. The deep peroneal nerve innervates the foot and toe extensors (tibialis anterior, extensor hallucis longus, extensor digitorum longus) and provides sensation to a small area between the great and second toes. The superficial peroneal nerve i nnervates the peroneus longus/brevis (foot eversion) and the skin of the distal anterior leg, the dorsum of the foot, and the digits. Lesions of the common peroneal nerve (most common) result in paralysis of dorsiflexion (foot-drop) and foot eversion. The posterior femoral cutaneous nerve (Sl-S3) innervates the skin of the inferior buttocks, perineum, posterior thigh, and proximal leg (Greenberg, pp. 522, 544-546).

Answer 44

A. Refer to Figure 2.68A. The corticospinal, frontopontine, superior thalamic radiations, and a relatively smaller number of corticotectal and corticorubral fibers run in the posterior limb of the internal capsule. The prefrontal corticopontine tract and anterior thalamic radiations run in the anterior limb of the internal capsule, while the corticobulbar and corticoreticular tracts are contained within the genu of the internal capsule (Carpenter, p. 282).

Answer 45

C . Although glutamate appears to be the main neurotransmitter of the corticothalamic tracts, the thalamus itself is rich in GABA. Virtually all cells of the thalamus are rich in this neurotransmitter; in primates, the major projections of the medial pallidum to the VA and VL nuclei of the thalamus are GABAergic. Moreover, the projections from the pars reticulata of the substantia nigra to the VA and MD nuclei of the thalamus are also rich in GABA (Carpenter, pp. 278- 2 79).

Answer 46

B. The LGN contains six layers, numbered 1 through 6. The ventralmost layers contain large cells and are known as "magnocellular"; they receive their input from M ganglion cells. The dorsal four layers are known as "parvocellular" and receive their input from P ganglion cells. An individual layer receives input from only one eye. Fibers from the contralateral nasal hemiretina synapse in layers 1, 4, and 6, and fibers from the ipsilateral temporal hemiretina synapse in layers 2, 3 , and 5 ( Ka ndel, pp. 528-532) .

Answer 47

B. The cerebellum comprises the fastigial, globose, emboliform, and dentate nuclei. The globose and emboliform nuclei together are known as the interposed nuclei. These nuclei correspond to the three functional dh•isions of the cerebellum: the vestibulocerebellum, spinocerebellum, and cerebrocerebellum. The vermis projects via the fastigial nucleus to the cortex and brainstem giving rise to the medial CHAPTER 2 Neuroanatomy Answers 45 descending systems controlling proximal musculature. The intermediate zone of the cerebellum projects via the interposed nuclei to cortical and brainstem regions, which giye rise to the lateral descending pathways controlling distal limb muscles. The lateral zone projects to the dentate nucleus, which forms connections with the motor and premotor areas of the cerebral cortex for the planning of voluntary movements (Carpenter, pp. 234-236) .

Answer 48

C. The motor strip generally lies 4 to 5.4 em behind the coronal suture (Greenberg, pp. 97 -98) .

Answer 49

(B) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 50

(F) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 51

(G) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 52

(D) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 53

(G) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 54

(H) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 55

(H) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 56

(E) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 57

(G) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 58

(B) The oculomotor (CN III), trochlear (CN IV) , and abducens nerves (VI) innervate the extraocular muscles and, along with the V1 and V2 divisions of CN V, exit the skull base through the superior orbital fissure (B). The trochlear (see question 84 for complete discussion) and abducens nerves provide GSE fibers to the superior oblique and lateral rectus muscles, respectively, while CN Ill innervates the levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Lesions of CN III will produce lateral strabismus ("wall eyes") with nearly complete ophthalmoplegia of the eye as well as ptosis. The Edinger-Westphal nucleus is the most rostral parasympathetic nucleus, which gives rise to the GVE component of the oculomotor nerve (CN III) . The facial nerve is both a sensory and motor nerve. The main motor nucleus of the facial nerve lies i n the reticular formation of the lower pons. Fibers leaving this nucleus course dorsally toward the floor of the fourth ventricle, loop around the abducens nucleus, and slightly indent the floor of the fourth ventricle, forming the facial colliculus. This loop is the internal genu of the facial nerve, which then turns ventrally to emerge on the ventrolateral part of the brainstem at the caudal border of the pons. This nerve then accompanies cranial nerve VIII through the internal auditory canal (G) and petrous temporal bone and exits the skull at the stylomastoid foramen. The nerve to the stapedius muscle is given off prior to exiting the skull, and injury to this small branch can result in hyperacusis. The remaining fibers exit the skull and innervate the frontalis (temporal nerve), orbicularis oculi (zygomatic nerve) , buccinator and orbicularis oris (buccal nerve ) , orbicularis oris (mandibular nerve), platysma (cervical nerve), and occipitalis muscles (posterior auricular nerve). The superior salh:_atory nucleus (SSN), which supplies the submandibular, salivary, and lacrimal glands, lies posterolaterally to the motor nucleus. The efferents from this nucleus travel via the nervus intermedius and divide i n the facial canal into two nerves called the greater petrosal (lacrimal and nasal glands) and the chorda tympani (submandibular gland) nerves. The greater petros.al nerve exits the petrous portion of the temporal bone via the greater superficial petrosal foramen (F) to enter the middle cranial fossa, passes deep to the trigeminal ganglion, traverses the lateral wall of the foramen lacerum, joins with the deep . . . 46 I ntensive Neurosurgery Hoard Review petrosal nerve carrying sympathetic fibers, and becomes the nerve of the pterygoid canal. It then synapses in the pterygopalatine ganglion prior to continuing forward to the lacrimal glan

Answer 59

C. The trochlear nucleus is located in the tegmentum of the mesencephalon at the level of the inferior colliculus, ventral to the cerebral aqueduct. Axons leaving this nucleus course dorsally around the aqueduct, decussate \Yithin the superior medullary velum, and exit the brainstem on the dorsal surface (only cranial nerve to exit the brain stem dorsally and decussate after exiting the brainstem). Since the trochlear nerve crosses to the other side, it innervates the contralateral superior oblique muscle. Of note, the trochlear nerve passes through the cavernous sinus along with cranial nerves III, V1, sometimes V2, and VI. Cranial nerves III, V1, V 2, and IV run along the lateral wall of the sinus, while cranial nerve VI runs more medially and adjacent to the internal carotid artery. Injury to the superior oblique muscle or trochlear nerve results in diplopia, with weakness of downward and medial gaze. Patients have most difficulty walking down stairs, and because of the tendency to tilt the head to compensate for the affected superior oblique muscle, fourth nerve palsies should be included in the differential for torticollis (Wilson-Pauwels, pp. 70-7 7 ) .

Answer 60

E . T h e corticospinal tracts originate in layer V o f the cerebral cortex, pass through the corona radiata and posterior limb of the internal capsule, form the middle third of the cerebral peduncles and the pyramids of the medulla, and terminate primarily on interneurons of lamina VII in the spinal cord. Approximately 40% of corticospinal fibers originate in the parietal lobe, 30% are from the motor cortex (area 4 ) , 30% from the supplementary motor area (area 6), and only 3% originate from the giant Betz pyramidal cells of the motor cortex. Around two-thirds of the corticospinal fibers are myelinated, and there are approximately 1 million corticospinal fibers in each pyramid of the medulla. Corticospinal fibers incompletely decussate in the medulla and form the large crossed lateral corticospinal tract (90% of fibers ) , the smaller uncrossed anterior corticospinal tract, and the very small uncrossed anterolateral corticospinal tract. The lateral corticospinal tracts descend in the lateral funiculus to all levels of the spinal cord and synapse in laminae IV, V, VI, and VII of the spinal gray. The anterior corticospinal tracts descend adjacent to the anterior median fissure of the spinal cord and terminate primarily in cervical segments. The majority of these fibers (90%) decussate at upper cervical levels of the spinal cord in the anterior white commissure before synapsing in lamina VII of the spinal gray. The uncrossed anterolateral corticospinal tracts (1 0%) descend ventral to the lateral corticospinal tracts to terminate in the intermediate gray and base of the posterior horns of the spinal cord. A relatively small number of corticospinal fibers synapse directly on motor neurons in the anterior horn of the spinal cord. Within the spinal cord, cervical corticospinal fibers are located medially, and sacral fibers are found laterally. The corticospinal tracts are responsible for voluntary skilled movements of the extremities . Significant corticospinal tract lesions may cause hypotonia followed by hyperactive deep tendon reflexes, extensor toe response (Babinski sign), and loss of superficial abdominal and cremasteric reflexes (Carpenter, pp. 94-97 ; Martin , pp. 144-145) .

Answer 61

A. The limbic lobe is not a true lobe of the brain but rather a functional collection of structures that regulates CHAPTER 2 Neuroanatomy Answers 4 7 higher activities such as memory and emotion. I t does not include the amygdala. Papez's circuit runs from the hippocampus to the fornix to the mammillary body. Fibers are then relayed to the anterior nucleus of the thalamus. (through the mammillothalamic tract) to the cingulate gyrus and back to the hippocampus through the cingulate bundle. The term limbic system includes the limbic lobe and its associated subcortical nuclei, including the amygdala, hypothalamus, septal, and certain hypothalamic nuclei (Kandel, pp. 986-987; Carpenter, pp. 376, 384-386).

Answer 62

C, The retina contains both electrical and chemical synapses. Photoreceptors and horizontal cells are connected to each other via gap junctions, but, as in the rest of the brain, chemical synapses predominate in the retina. Most are calcium-independent and appear to work by cGMP. (See discussion for question 27 in Chapter 1, Neurobiology Answers, for further discussion of phototransduction.) (Kandel , pp. 492-506).

Answer 63

A. The innermost retinal cell layer (ganglion cell layer) is named after the retinal output cells. The axons of ganglion cells are unmyelinated, whict1 facilitates light transmission to the photoreceptor layer of the outer retina. The layers superficial to the ganglion cell layer include the inner synaptic (plexiform) layer, inner nuclear layer, outer synaptic (plexiform) layer, and outer nuclear layer. The outer nuclear layer contains the cell bodies of the rods (night vision) and cones (daylight vision). The inner nuclear layer contains the cell bodies of the retinal interneurons, which include the bipolar cells., horizontal cells, and amacrine cells. Bipolar cells link photoreceptors directly with the ganglion cells, while the _actions of horizontal and amacrine cells enhance visual contrast through interactions between laterally located photoreceptor cells and bipolar cells. Horizontal cells are located. on the outer part of the inner nuclear layer, while amacrine cells are located on the inner portion. Amacrine cells contain dopamine. Muller cells are the principal retinal neuroglial cells ( Marti n , p p . 164-171; Kandel, p. 515).

Answer 64

(M) (Fix, p. 208; Carpenter, p. 262).

Answer 65

(E) (Fix, p. 208; Carpenter, p. 262).

Answer 66

(F) (Fix, p. 208; Carpenter, p. 262).

Answer 67

(I) (Fix, p. 208; Carpenter, p. 262).

Answer 68

(K) (Fix, p. 208; Carpenter, p. 262).

Answer 69

(J) (Fix, p. 208; Carpenter, p. 262).

Answer 70

(L) (Fix, p. 208; Carpenter, p. 262).

Answer 71

(D)(Fix, p. 208; Carpenter, p. 262).

Answer 72

(D) Refer to Figure 2 . 96A. The medulla oblongata contains GVE fibers that originate in the inferior salivatory nucleus and gives rise to the fibers that synapse in the otic ganglia to control parotid gland secretion. It also contains the nucleus ambiguus, which gives rise to the vagal preganglionic p;uasympathetic GVE fibers that syqapse in the sinoatrial and atrioventricular nodes of the heart. The medulla extend from the pyramidal decussation to the inferior pontine sulcus and also contains the corticospinal tracts, medial lemniscus, medial longitudinal fasciculus, hypoglossal nuclei. oli\•ary nuclei, spinal lemniscus, spinocerebellar tracts, spinal trigeminal tract and nucleus, inferior cerebellar peduncle, dorsal motor nucleus of CN X, solitary tract, CN nuclei of IX to XI" (although it also houses portions of CN V and CN VIII ) , as well as the inferior and medial vestibular nuclei. The lateral vestibular nuclei are mainly in the pons. The medulla receives its blood supply from the posterior spinal artery, anterior spinal artery, PICA, and branches originating from the vertebral arteries (Carpenter, pp. 1 15-150) .

Answer 73

D. The most likely cause of the constellation of signs/symptoms reported in this patient is a lesion in the dorsolateral zone of the pontine isthmus on the left side (lateral superior pontine syndrome). Interruption of the descending sympathetic tract resulted in the ipsilateral Horner's syndrome. I nvolvement of the lateral aspect (includes leg fibers) of the medial lemniscus resulted in loss of vibratory sensation and other dorsal column deficits on the contralateral side. Damage to the trigeminothalamic tract and spinothalamic tracts in this location would account for the contralateral hemianesthesia of the face and body. Disruption of the superior cerebellar peduncle can lead to the severe ataxia and tremor on the ipsilateral side (Carpenter, pp. 151-191; Fix, pp. 184-186). 98. A. Refer to Figure 2.

Answer 74

A. Paramedian midbrain (Benedikt's) syndrome results from occlusion of the paramedian midbrain branches of the PCA and/or basilar artery. Structures affected include the CN III nerve roots (eye abduction and depression due to unopposed action of lateral rectus and superior oblique muscles) as well as the red nucleus and dentatorubrothalamic tract (intention tremor and ataxia). Medial midbrain (Weber's) syndrome results from occlusion of medial midbrain branches, which can result in CN III palsy, corticobulbar tract injury (contralateral facial weakness) , and corticospinal tract injury (contralateral hemiparesis or hemiplegia) (Fix, pp. 187-188; Carpenter, pp. 192-223) . FIGURE 2.98A Mesencephalon. This transverse section illustrates the midbrain at the level of the superior colliculus. CN, cranial nerve; MLF, medial longitudinal fasciculus. (Reprinted with permission from Moore SP. The Definitive Neurological Surgery Board Review. Malden, 1\•L

Answer 75

E. The gustatory system innervates the special visceral afferent (SVA) modality of taste. Taste buds located on the tongue, epiglottis, and palate are innervated by the SVA fibers of CN VII, IX, and X. First-order neurons are pseudounipolar ganglion cells located in the geniculate ganglion of CNV II, the petrosal ganglion of IX, and the nodose ganglion of X. These fibers project centrally to the solitary nucleus, which then projects, via the central tegmental tract, to the parabrachial nucleus of the pons and VPM nucleus of the thalamus. The parabrachial nucleus then projects to the hypothalamus and amygdala, whereas the VPM projects to gustatory area 43 (parietal operculum) and parainsular cortex. Area 43 then projects via way of the en to rhinal cortex to the hippocampal formation. The parabigeminal nucleus functions with the superior colliculus in processina visual information ( Fix, pp. 254-256, Carpenter, pp. 137, 140, 143, 171, 2 7 1 , 418 ) .

Answer 76

E . T h e parafascicular, centromedian, and rostral intralaminar nuclei of the thalamus lie within the internal medullary lamina and are known as the intralaminar nuclei of the thalamus. The parafascicular nucleus of the thalamus lies medial to the centromedian nucleus and ventral to the dorsomedial nuclei of the thalamus. While the projections of the parafascicular and centromedian nuclei of the thalamus CHAPTER 2 Neuroanatomy Answers 49 remain ill-defined, the majority are believed to terminate in the striatum. Cells of the centromedian nucleus project principally to the putamen, where they terminate i n a mosaic-type pattern, and cells from the parafascicular• nucleus project to the caudate nucleus. Few tracts project to both regions of the striatum. The majority of motor activities are influenced by the thalamus, cerebellum, basal ganglia, peripheral receptors, and other cortical areas. The basal ganglia and cerebellum provide priming and feedback functions for smoothly executed movements. Sensory feedback concerning position sense are provided by the dorsal columnmedial lemniscus (via the ventral posterior lateral [VPL] nucleus of the thalamus) , which is necessary to make both accurate and sequential movements. Complex voluntary motor activity is aided by the premotor region of the posterior parietal region (area 5 ) , which helps with goal-directed movements that require transformation of sensory representations of the environment into limb and hand movements, a process termed sensorimotor transformation (Carpenter, pp. 424-425; Kandel, pp. 756-7 79).

Answer 77

B. Nitric oxide is synthesized from the amino acid arginine by the enzyme nitric oxide synthase (NOS). Nitric oxide easily diffuses across the plasma membrane of target cells. Within target cell

Answer 78

B. The Bell-1viagendie law states that all motor fibers exit the spinal cord via the ventral roots and all sensory fibers enter the spinal cord via the dorsal roots. Unmyelinated C fibers that transmit pain and temperature information from the pelvic viscera reside in the ventral roots from L5 to S3, thus violating the Bell-Magendie law. The-cell bodies of these neurons reside in the dorsal root ganglia, like other sensory neurons (DeMyer, p. 55).

Answer 79

C. The reticulospinal tracts originate largely i n the brainstem reticular formation (pons and medulla) and project to all spinal• levels. The raphe nuclei of the reticular formation contain serotonergic projections that compose a portion of the reticulospinal tracts. These serotonergic projections synapse in laminae I, II, and V of the spinal cord (especially cervical levels) to influence afferent nociceptive impulses from the periphery (Carp

Answer 80

D. Efferent fibers from the substantia nigra proJect to the striatum (pars compac.ta efferents) and thalamus (pars reticulata efferents). Nigrothalamic fibers terminate primarily in the VA and MD thalamic nuclei. A small component of efferent fibers from the pars reticulata also project to the pedunculopontine nucleus (Carpenter, pp. 2 18-220) .

Answer 81

B. The medial forebrain bundle sends fibers from the basal olfactory regfons, the septal nuclei, the periamygdaloid region, and the subiculum to the lateral preoptic and hypothalamic regions (Carpenter, p. 304) .

Answer 82

(I) . (Osborn DCA, pp. 2 1 7-223)

Answer 83

(L) . (Osborn DCA, pp. 2 1 7-223)

Answer 84

(G) . (Osborn DCA, pp. 2 1 7-223)

Answer 85

(H) . (Osborn DCA, pp. 2 1 7-223)

Answer 86

(C) . (Osborn DCA, pp. 2 1 7-223)

Answer 87

(E) . (Osborn DCA, pp. 2 1 7-223)

Answer 88

(D) . (Osborn DCA, pp. 2 1 7-223)

Answer 89

(J) . (Osborn DCA, pp. 2 1 7-223)

Answer 90

(B) . (Osborn DCA, pp. 2 1 7-223)

Answer 91

(A) . (Osborn DCA, pp. 2 1 7-223)

Answer 92

(F) . (Osborn DCA, pp. 2 1 7-223)

Answer 93

(M) . (Osborn DCA, pp. 2 1 7-223)

Answer 94

(K) . (Osborn DCA, pp. 2 1 7-223)

Answer 95

A . The first dorsal root frequently undergoes regression and disappears. The front part of the scalp (forehead) is innervated by CN V: supraorbital and supratrochlear nerves (V1), zygomaticotemporal nerve (V2), and the auriculotemporal nerve (V3) . The occipital region is innervated by the greater occipital nerve (C2), the lesser occipital nerve (C2- 3), the least occipital nerve (C3), and the great auricular nerve (C2-3) (April , p. 427).

Answer 96

D. The Schwann cells and fibrous connective tissue stop abruptly at a site where the nerve roots meet the spinal cord and/or brainstem. Central to this junction, glial connective tissue is composed of oligodendrocytes, whereas in the peripheral nervous system, Schwann cells replace oligodendrocytes. This junction is called the Obersteiner-Redlich zone ( DeMyer, p. 59).

Answer 97

A. The nerve that innervates the fifth digit, C8, travels through the medial cord of the brachial plexus and down the arm in the ulnar nerve. Therefore, a lesion anywhere along this course may produce pain and numbness in the little fingeL The precise localization in this patient would likely require the presence of other concomitant neurologic abnormalities and obtaining nerve conduction or perhaps neuroimaging studies. C 7 nerve root abnormalities often cause problem.s with the third and fourth digits ( B razis, pp. 16-21, 59:60, 72).

Answer 98

The majority of posterior circulation aneurysms may be adequately exposed for surgical treatment through either a modification of the transsylvian approach or the far lateral suboccipital approach, which has also been referred to as the Extreme Lateral Inferior Transcondylar Exposure (ELITE) . With extensive opening of the posterior lateral portion of the cavernous sinus through a• transsylvian approach and by working through the space lateral to the oculomotor nerve, the upper and mid-basilar trunk can be successfully exposed to the level of the anterior inferior cerebellar artery (AICA). The ELITE exposure most often provides satisfactory exposure of the vertebral arteries bilaterally and the lower basilar trunk. The portion of the basilar trunk rostral to AICA origin assumes a distinctly midline location in the- majority of circumstances; it becomes increasingly difficult to control and visualize during rostral dissection due to the prominence of the ventral pons and the envelopment of the basilar artery by the brainstem as it enters the interpeduncular cistern. In select cases (giant aneurysms, cavernomas, or tumors of the dorsolateral pons) , • additional exposure may be obtained by a presigmoid corridor by removal of a portion of the petrous temporal bone, which may lessen the amount of brainstem or cerebellar retraction, as depicted here. The trochlear nerve (IV) is particularly vulnerable to injury while dividing the tentorium, and the superior petrosal sinus is often cauterized and divided during this exposure in order to mobilize the transverse and sigmoid sinuses (and quadrangular lobe of the cerebellum) as a single unit ( Kopitn i k, pp. 24-2 7)

Answer 99

The majority of posterior circulation aneurysms may be adequately exposed for surgical treatment through either a modification of the transsylvian approach or the far lateral suboccipital approach, which has also been referred to as the Extreme Lateral Inferior Transcondylar Exposure (ELITE) . With extensive opening of the posterior lateral portion of the cavernous sinus through a• transsylvian approach and by working through the space lateral to the oculomotor nerve, the upper and mid-basilar trunk can be successfully exposed to the level of the anterior inferior cerebellar artery (AICA). The ELITE exposure most often provides satisfactory exposure of the vertebral arteries bilaterally and the lower basilar trunk. The portion of the basilar trunk rostral to AICA origin assumes a distinctly midline location in the- majority of circumstances; it becomes increasingly difficult to control and visualize during rostral dissection due to the prominence of the ventral pons and the envelopment of the basilar artery by the brainstem as it enters the interpeduncular cistern. In select cases (giant aneurysms, cavernomas, or tumors of the dorsolateral pons) , • additional exposure may be obtained by a presigmoid corridor by removal of a portion of the petrous temporal bone, which may lessen the amount of brainstem or cerebellar retraction, as depicted here. The trochlear nerve (IV) is particularly vulnerable to injury while dividing the tentorium, and the superior petrosal sinus is often cauterized and divided during this exposure in order to mobilize the transverse and sigmoid sinuses (and quadrangular lobe of the cerebellum) as a single unit ( Kopitn i k, pp. 24-2 7)

Answer 100

The majority of posterior circulation aneurysms may be adequately exposed for surgical treatment through either a modification of the transsylvian approach or the far lateral suboccipital approach, which has also been referred to as the Extreme Lateral Inferior Transcondylar Exposure (ELITE) . With extensive opening of the posterior lateral portion of the cavernous sinus through a• transsylvian approach and by working through the space lateral to the oculomotor nerve, the upper and mid-basilar trunk can be successfully exposed to the level of the anterior inferior cerebellar artery (AICA). The ELITE exposure most often provides satisfactory exposure of the vertebral arteries bilaterally and the lower basilar trunk. The portion of the basilar trunk rostral to AICA origin assumes a distinctly midline location in the- majority of circumstances; it becomes increasingly difficult to control and visualize during rostral dissection due to the prominence of the ventral pons and the envelopment of the basilar artery by the brainstem as it enters the interpeduncular cistern. In select cases (giant aneurysms, cavernomas, or tumors of the dorsolateral pons) , • additional exposure may be obtained by a presigmoid corridor by removal of a portion of the petrous temporal bone, which may lessen the amount of brainstem or cerebellar retraction, as depicted here. The trochlear nerve (IV) is particularly vulnerable to injury while dividing the tentorium, and the superior petrosal sinus is often cauterized and divided during this exposure in order to mobilize the transverse and sigmoid sinuses (and quadrangular lobe of the cerebellum) as a single unit ( Kopitn i k, pp. 24-2 7)

Answer 101

(A) Bilateral lesions of the lateral hypothalamus abolishes the desire to eat, while lesions in the posterior hypothalamus can result in precocious puberty and excessive sleepiness, lethargy, and hypothermia. Lesions of the anterior hypothalamus can result in hyperthermia, while lesions in the arcuate nuclei and paraventricular region can result in decreased dopamine synthesis (Carpenter, pp. 125-129).

Answer 102

(C) Bilateral lesions of the lateral hypothalamus abolishes the desire to eat, while lesions in the posterior hypothalamus can result in precocious puberty and excessive sleepiness, lethargy, and hypothermia. Lesions of the anterior hypothalamus can result in hyperthermia, while lesions in the arcuate nuclei and paraventricular region can result in decreased dopamine synthesis (Carpenter, pp. 125-129).

Answer 103

(B) Bilateral lesions of the lateral hypothalamus abolishes the desire to eat, while lesions in the posterior hypothalamus can result in precocious puberty and excessive sleepiness, lethargy, and hypothermia. Lesions of the anterior hypothalamus can result in hyperthermia, while lesions in the arcuate nuclei and paraventricular region can result in decreased dopamine synthesis (Carpenter, pp. 125-129).

Answer 104

(A) Bilateral lesions of the lateral hypothalamus abolishes the desire to eat, while lesions in the posterior hypothalamus can result in precocious puberty and excessive sleepiness, lethargy, and hypothermia. Lesions of the anterior hypothalamus can result in hyperthermia, while lesions in the arcuate nuclei and paraventricular region can result in decreased dopamine synthesis (Carpenter, pp. 125-129).

Answer 105

(D) Bilateral lesions of the lateral hypothalamus abolishes the desire to eat, while lesions in the posterior hypothalamus can result in precocious puberty and excessive sleepiness, lethargy, and hypothermia. Lesions of the anterior hypothalamus can result in hyperthermia, while lesions in the arcuate nuclei and paraventricular region can result in decreased dopamine synthesis (Carpenter, pp. 125-129).

Answer 106

C. The inferior parietal lobule is composed of two gyri: the angular and supramarginal. The inferior parietal lobule represents a cortical association area, where multisensory signals from adjacent parietal, temporal, and occipital regions converge. The interparietal sulcus divides the parietal lobe into the superior and inferior parietal lobules (Carpenter, p. 2 7 ) .

Answer 107

C . Acoustic reflex mechanisms involve t h e middle ear muscles, such as the stapedius and tensor tympani. The stapedius muscle (CN VII) serves to dampen the oscillations of the middle ear ossicles in response to loud sounds, while contraction of the tensor tympani muscle (CN V) diminishes the sensitivity of sound by tensing the tympanic membrane. These acoustic reflex mechanisms are initiated by fibers originating in the superior olivary nucleus (Carpenter, p. 159).

Answer 108

E. The spinal trigeminal tract merges with the principal sensory nucleus rostrally (not the solitary nucleus), while caudally it blends into the substantia gelatinosa of the first two cervical spinal segments. Fibers of the ophthalmic division are most ventral, fibers of the mandibular division are most dorsal, and fibers from the maxillary division are intermediate (Carpenter, p. 1 7 7 ) .

Answer 109

. A . The best-known pineal secretions are the biogenic amines (serotonin, melatonin, and norepinephrine), but the gland also contains significant concentrations of hypothalamic peptides, such as thyrotropin-releasing hormone, leuteinizing hormone-releasing hormone, and somatostatin. Substance P is not known to be present in high concentrations in the pineal gland (Carpenter, pp. 253-254).

Answer 110

B. Melanocytes are located in the leptomeninges are most often located in the ventral medulla and upper levels of the cervical spinal cord (Ellison, pp. 734-737).

Answer 111

A. The intervertebral disc is a fibrocartilaginous remnant of the embryologic notochord (Youmans, p. 4327 ) .

Answer 112

A. The internal capsule is supplied primarily by the lateral lenticulostriate branches from the middle cerebral artery. Additionally, the medial striate artery (of Heubner) supplies the rostromedial parts of the anterior limb of the internal capsule, the genu receives direct branches from the internal carotid artery, while parts of the posterior limb and the entire retrolenticular capsule are supplied by the anterior choroidal artery (Carpenter, p. 448 ) .

Answer 113

A. The internal capsule is supplied primarily by the lateral lenticulostriate branches from the middle cerebral artery. Additionally, the medial striate artery (of Heubner) supplies the rostromedial parts of the anterior limb of the internal capsule, the genu receives direct branches from the internal carotid artery, while parts of the posterior limb and the entire retrolenticular capsule are supplied by the anterior choroidal artery (Carpenter, p. 448 ) .

Answer 114

C . Taste sensation is carried by t h e facial (VII), glossopharyngeal (IX), and vagus nerves (X) . The gustatory afferents end primarily in the nucleus of the tractus solitarius in the medulla (Brazis, p. 273).

Answer 115

D . The spinal accessory nerve (XI) does not carry parasympathetic fibers but instead carries branchial motor fibers to the sternocleidomastoid and trapezius muscles (Wilson-Pauwels, p. 205) .

Answer 116

(F) (Greenberg, pp. 520-521).

Answer 117

(H) (Greenberg, pp. 520-521).

Answer 118

(C) (Greenberg, pp. 520-521).

Answer 119

(G) (Greenberg, pp. 520-521).

Answer 120

(I) (Greenberg, pp. 520-521).

Answer 121

(E) (Greenberg, pp. 520-521).

Answer 122

(D) (Greenberg, pp. 520-521).

Answer 123

(A) (Greenberg, pp. 520-521).

Answer 124

(B) (Greenberg, pp. 520-521).

Answer 125

(C) The orbitofrontal cortex is linked to the limbic and reticular areas; therefore lesions of this area can lead to behavioral abnormalities. Il•1ost commonly, orbitofrontal (frontal pole) lesions can result in euphoria, emotional lability, poor judgment and insight, explosiveness, and distractibility. The lateral frontal cortex is linked to motor structures, therefore damage to this area can lead to disturbances of action with apathy, indifference, psychomotor retardation, motor preservation and impersistence, and poor abstraction. The medial frontal syndrome is associated with mutism, gait disturbances, incontinence, "salutatory seizures," "alien hand syndrome," and apraxia of gait or "magnetic gait" (paracentral lobule) . Exploring objects orally i s a feature o f temporal lobe dysfunction (Brazis, pp. 4 73-4 7 4, 509, 522-524) .

Answer 126

(B) The orbitofrontal cortex is linked to the limbic and reticular areas; therefore lesions of this area can lead to behavioral abnormalities. Il•1ost commonly, orbitofrontal (frontal pole) lesions can result in euphoria, emotional lability, poor judgment and insight, explosiveness, and distractibility. The lateral frontal cortex is linked to motor structures, therefore damage to this area can lead to disturbances of action with apathy, indifference, psychomotor retardation, motor preservation and impersistence, and poor abstraction. The medial frontal syndrome is associated with mutism, gait disturbances, incontinence, "salutatory seizures," "alien hand syndrome," and apraxia of gait or "magnetic gait" (paracentral lobule) . Exploring objects orally i s a feature o f temporal lobe dysfunction (Brazis, pp. 4 73-4 7 4, 509, 522-524) .

Answer 127

(A) The orbitofrontal cortex is linked to the limbic and reticular areas; therefore lesions of this area can lead to behavioral abnormalities. Il•1ost commonly, orbitofrontal (frontal pole) lesions can result in euphoria, emotional lability, poor judgment and insight, explosiveness, and distractibility. The lateral frontal cortex is linked to motor structures, therefore damage to this area can lead to disturbances of action with apathy, indifference, psychomotor retardation, motor preservation and impersistence, and poor abstraction. The medial frontal syndrome is associated with mutism, gait disturbances, incontinence, "salutatory seizures," "alien hand syndrome," and apraxia of gait or "magnetic gait" (paracentral lobule) . Exploring objects orally i s a feature o f temporal lobe dysfunction (Brazis, pp. 4 73-4 7 4, 509, 522-524) .

Answer 128

(D) The orbitofrontal cortex is linked to the limbic and reticular areas; therefore lesions of this area can lead to behavioral abnormalities. Il•1ost commonly, orbitofrontal (frontal pole) lesions can result in euphoria, emotional lability, poor judgment and insight, explosiveness, and distractibility. The lateral frontal cortex is linked to motor structures, therefore damage to this area can lead to disturbances of action with apathy, indifference, psychomotor retardation, motor preservation and impersistence, and poor abstraction. The medial frontal syndrome is associated with mutism, gait disturbances, incontinence, "salutatory seizures," "alien hand syndrome," and apraxia of gait or "magnetic gait" (paracentral lobule) . Exploring objects orally i s a feature o f temporal lobe dysfunction (Brazis, pp. 4 73-4 7 4, 509, 522-524) .

Answer 129

(C) The orbitofrontal cortex is linked to the limbic and reticular areas; therefore lesions of this area can lead to behavioral abnormalities. Il•1ost commonly, orbitofrontal (frontal pole) lesions can result in euphoria, emotional lability, poor judgment and insight, explosiveness, and distractibility. The lateral frontal cortex is linked to motor structures, therefore damage to this area can lead to disturbances of action with apathy, indifference, psychomotor retardation, motor preservation and impersistence, and poor abstraction. The medial frontal syndrome is associated with mutism, gait disturbances, incontinence, "salutatory seizures," "alien hand syndrome," and apraxia of gait or "magnetic gait" (paracentral lobule) . Exploring objects orally i s a feature o f temporal lobe dysfunction (Brazis, pp. 4 73-4 7 4, 509, 522-524) .

Answer 130

(C) The orbitofrontal cortex is linked to the limbic and reticular areas; therefore lesions of this area can lead to behavioral abnormalities. Il•1ost commonly, orbitofrontal (frontal pole) lesions can result in euphoria, emotional lability, poor judgment and insight, explosiveness, and distractibility. The lateral frontal cortex is linked to motor structures, therefore damage to this area can lead to disturbances of action with apathy, indifference, psychomotor retardation, motor preservation and impersistence, and poor abstraction. The medial frontal syndrome is associated with mutism, gait disturbances, incontinence, "salutatory seizures," "alien hand syndrome," and apraxia of gait or "magnetic gait" (paracentral lobule) . Exploring objects orally i s a feature o f temporal lobe dysfunction (Brazis, pp. 4 73-4 7 4, 509, 522-524) .

Answer 131

A. The vertebral artery usually travels through the transverse foramina of C6 through C2 prior to exiting the transverse foramen of the axis and curving posteriorly and superiorly in a groove on the upper surface of the atlas (Greenberg, p. 107).

Answer 132

B. An afferent pupillary defect (Marcus Gunn pupil) can be diagnosed by the "swinging flashlight test." This pupillary sign is characterized by normal bilateral pupillary responses when the normal eye is illuminated, CHAPTER 2 Neuroanatomy Answers 51 but pupillary dilation occurs when the flashlight is quickly switched to the affected eye. This abnormality may be seen with lesions involving the macula, retina, optic nerve, optic tract, brachium of the superior colliculus, or pretectal nucleus ( Kline, pp. 1 2 7-128, Brazis, pp. 144-145).

Answer 133

C. An afferent pupillary defect (Marcus Gunn pupil) can be diagnosed by the "swinging flashlight test." This pupillary sign is characterized by normal bilateral pupillary responses when the normal eye is illuminated, CHAPTER 2 Neuroanatomy Answers 51 but pupillary dilation occurs when the flashlight is quickly switched to the affected eye. This abnormality may be seen with lesions involving the macula, retina, optic nerve, optic tract, brachium of the superior colliculus, or pretectal nucleus ( Kline, pp. 1 2 7-128, Brazis, pp. 144-145).

Answer 134

C. The superior rectus (medial subnucleus of the oculomotor nucleus, CN III) and superior oblique (trochlear nucleus, CN IV) muscles receive contralateral nuclear innervation (Wilson-Pauwels, pp. 53, 70).

Answer 135

B . "Periodic alternating gaze" (PAG) consists of cyclic conjugate lateral deviation of the eyes with compensatory head turning towards the opposite side (1 to 2 minutes), a midline changeover period ( 1 0 to 15 seconds), which is followed by conjugate deviation of the eyes toward the other side (with compensatory head turning). It is most common with diseases of the posterior fossa (pontine damage, posterior fossa ischemia, medulloblastoma, and Chiari malformations) (Brazis, pp. 212-2 13)

Answer 136

(B) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 137

(E) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 138

(D) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 139

(D) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 140

(A) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 141

(C) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 142

(A) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 143

(F) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 144

(F) The trigeminal nerve afferents mediate the tearing and corneal reflex (V1), sneeze reflex (V2) , and jaw-jerk reflex (V3) . The vagus nerve (X) mediates the afferent limb of the cough reflex, while the glossopharyngeal nerve (IX) mediates the afferent limb of the carotid sinus and gag reflexes. The optic nerve innervates the afferent limb of the pupillary reflex via the Edinger-Westphal nucleus (DeMyer, pp. 1 7 1 , 176-1 7 7 ) .

Answer 145

D. The ganglionic cells o f the retina are considered to be cholinergic, while some of the neurons of the striatum, dorsal horn, cerebellum, collicular plate, substantia nigra, hypothalamus, pallidum, and anterior perforated substance (substantia innominata) are considered to be GABAergic (DeMyer, pp. 384-385).

Answer 146

D. Since the secondary cochlear pathways are both crossed and uncrossed, lesions of one lateral lemniscus can result in partial bilateral deafness. I njury to the inner hair cells of the cochlea, cochlear nerve, or ventral and dorsal cochlear nuclei produces unilateral hearing loss (Brazis, pp. 293-295)

Answer 147

(F) Majo'r sites of origin of the various neurotransmitters are as follows: acetylcholinegigantocellular complex of the basal forebrain including the basal nucleus (of Meynert) ; GABA-golgi type II interneurons as well as various areas of the hypothalamus, substantia nigra, cerebellum, dorsal horns, collicular plate, and substantia innominata; dopamine-ventral tegmental region/ substantia nigra of • midbrain, serotonin-raphe nuclei of midbrain; norepinephrine-locus ceruleus (DeMyer, p. 385; Carpenter, pp. 128, 131) .

Answer 148

(B) Majo'r sites of origin of the various neurotransmitters are as follows: acetylcholinegigantocellular complex of the basal forebrain including the basal nucleus (of Meynert) ; GABA-golgi type II interneurons as well as various areas of the hypothalamus, substantia nigra, cerebellum, dorsal horns, collicular plate, and substantia innominata; dopamine-ventral tegmental region/ substantia nigra of • midbrain, serotonin-raphe nuclei of midbrain; norepinephrine-locus ceruleus (DeMyer, p. 385; Carpenter, pp. 128, 131) .

Answer 149

(A) Majo'r sites of origin of the various neurotransmitters are as follows: acetylcholinegigantocellular complex of the basal forebrain including the basal nucleus (of Meynert) ; GABA-golgi type II interneurons as well as various areas of the hypothalamus, substantia nigra, cerebellum, dorsal horns, collicular plate, and substantia innominata; dopamine-ventral tegmental region/ substantia nigra of • midbrain, serotonin-raphe nuclei of midbrain; norepinephrine-locus ceruleus (DeMyer, p. 385; Carpenter, pp. 128, 131) .

Answer 150

(B) Majo'r sites of origin of the various neurotransmitters are as follows: acetylcholinegigantocellular complex of the basal forebrain including the basal nucleus (of Meynert) ; GABA-golgi type II interneurons as well as various areas of the hypothalamus, substantia nigra, cerebellum, dorsal horns, collicular plate, and substantia innominata; dopamine-ventral tegmental region/ substantia nigra of • midbrain, serotonin-raphe nuclei of midbrain; norepinephrine-locus ceruleus (DeMyer, p. 385; Carpenter, pp. 128, 131) .

Answer 151

(C) Majo'r sites of origin of the various neurotransmitters are as follows: acetylcholinegigantocellular complex of the basal forebrain including the basal nucleus (of Meynert) ; GABA-golgi type II interneurons as well as various areas of the hypothalamus, substantia nigra, cerebellum, dorsal horns, collicular plate, and substantia innominata; dopamine-ventral tegmental region/ substantia nigra of • midbrain, serotonin-raphe nuclei of midbrain; norepinephrine-locus ceruleus (DeMyer, p. 385; Carpenter, pp. 128, 131) .

INBR 7 - Neuroanatomy Flashcards

(175 cards)