Chapter 14: Brain and Cranial Nerves Flashcards
1
Q
Telencephalon.
A
Forms cerebrum and lateral ventricles.
2
Q
Diencephalon.
A
Forms thalamus, hypothalamus, epithalamus and third ventricle. Superior to brainstem.
3
Q
Mesencephalon.
A
Forms midbrain and cerebral aqueduct.
4
Q
Metencephalon.
A
Forms pons, cerebellum and upper fourth ventricle.
5
Q
Myencephalon.
A
Forms medulla oblongata and lower fourth ventricle.
6
Q
Brainstem.
A
Continuous with spinal cord. Consists of medulla oblongata, pons and midbrain.
7
Q
Where is the cerebellum?
A
Posterior to brainstem.
8
Q
What is the largest part of the brain?
A
Cerebrum.
9
Q
Describe the dura mater in the brain, and its layers.
A
Continuous with the dura mater in the spinal cord. Consists of an outer periosteal layer and an inner meningeal layer. These layers are fused together except for where they separate to enclose the dural Venus sinuses that drain venous blood from the brain.
10
Q
What are the 3 extensions of the dura mater in the brain that separate parts of the brain?
A
Falx cerebri: separates the 2 sides of the cerebrum. Falx cerebelli: separates the 2 sides of the cerebellum. Tentorium cerebelli: separates the cerebrum from the cerebellum.
11
Q
What is present in the spinal cord, but not in the brain?
A
Epidural space.
12
Q
What are the main routes of blood flow to the brain?
A
Internal carotid artery and vertebral arteries.
13
Q
What is the main route of blood flow from the brain?
A
The dural venous sinuses drain into the internal jugular veins.
14
Q
How much oxygen and glucose does the brain consume?
A
20% of the body’s supply.
15
Q
An interruption of blood flow for how many minutes distinguishes between impaired function vs. permanent damage?
A
Impaired neuronal function: 1-2 minutes. Permanent injury: 4 minutes.
16
Q
Why must the supply of glucose to the brain be continuous?
A
No glucose is stored in the brain.
17
Q
What are the components of the blood brain barrier?
A
Tight junctions between endothelial cells, and a thick basement membrane that surrounds the capillaries.
18
Q
Which substances can diffuse across the BBB?
A
Lipid soluble, steroid hormones, alcohols, barbiturates, nicotine, caffeine, water molecules.
19
Q
What causes breakdown of the BBB?
A
Trauma, toxins, inflammation.
20
Q
Cerebrospinal fluid.
A
Clear and colourless liquid composed of mostly water. Protects the brain and spinal cord from chemical and physical injuries.
21
Q
What are the components of CSF?
A
Water, oxygen, glucose, proteins, lactic acid, urea, cations, anions, WBCs.
22
Q
How much CSF is in the body at all times, and how much is produced?
A
80-150 mL. Body produces 20 mL / hour.
23
Q
What are the CSF-filled cavities in the brain?
A
Lateral ventricle 1, lateral ventricle 2, third ventricle and fourth ventricle.
24
Q
What is the difference between lateral ventricles 1 and 2?
A
Each one is in its own hemisphere of the cerebrum.
25
What separates the lateral ventricles 1 and 2?
Septum pellucidum.
26
Third ventricle.
Narrow slit-like cavity along the midline. Located superior to the hypothalamus between the right and left halves of the thalamus.
27
Where is the fourth ventricle located?
Between brainstem and cerebellum.
28
What are the 3 functions of the CSF?
1) Mechanical protection: shock-absorbing. 2) Chemical protection: provides a chemical environment optimal for neuronal signalling. 3) Circulation: exchange of nutrients and waste between blood and nervous tissue.
29
How is CSF produced?
By ependymal cells of choroid plexuses in the ventricle walls.
30
What is the blood-CSF barrier?
Formed by tight junctions between ependymal cells.
31
Describe CSF circulation.
CSF flows from lateral ventricles to third ventricle through interventricular foramina --> more CSF is added by choroid plexus in roof of third ventricle --> flows through cerebral aqueduct --> midbrain --> fourth ventricle --> more CSF is added by choroid plexus in fourth ventricle --> flows to subarachnoid space through a single median aperture and paired lateral apertures --> to central canal of spinal cord --> gradually reabsorbed into blood through arachnoid villi.
32
Medulla oblongata.
Continuous with the superior part of the spinal cord, and forms the inferior part of the brainstem. Begins at the foramen magnum and extend to the inferior border of the pons.
33
Describe the white matter of the medulla oblongata.
Contains all sensory and motor tracts that extend between the spinal cord and the brain. Some of the white matter forms pyramids.
34
Pyramids.
Formed by large corticospinal tracts that pass from cerebrum to spinal cord.
35
Decussation of pyramids.
90% of axons in the left pyramid cross to the right side, and 90% of axons in the right pyramid cross to the left side. Explains why each side of the brain controls voluntary movements on the opposite side of the body.
36
Where is the cardiovascular centre, and what is its function?
Medulla oblongata. Regulates rate and force of heartbeat and diameter of blood vessels.
37
Where is the medullary respiratory centre, and what is its function?
Medulla oblongata. Adjusts basic rhythm of breathing.
38
Where is the vomiting centre?
Medulla oblongata.
39
Where is the deglutition centre, and what is its function?
Medulla oblongata. Promotes swallowing.
40
Which brain structure controls sneezing, coughing and hiccupping reflexes?
Medulla oblongata.
41
Olive.
Lateral to each pyramid. Contains an inferior olivary nucleus, which receives input from the cerebral cortex, red nucleus and spinal cord, and sends output to the cerebellum.
42
What is the function of the inferior olivary nucleus?
Provides instructions for the cerebellum to make adjustments to muscle movement.
43
Where are the gracile nucleus and cuneate nucleus, and what are their functions?
Posterior medulla oblongata. Monitor touch, pressure, vibration and conscious proprioception, and send impulses to thalamus on opposite side of the brain in a medial lemniscus.
44
Where is the gustatory nucleus, and what is its function?
Medullary oblongata. Receives gustatory input from the tongue taste buds.
45
Where are the cochlear nuclei, and what is their function?
Medulla oblongata. Receive auditory input from cochlea of inner ear.
46
Where are the vestibular nuclei, and what is there function?
Medulla oblongata. Receive equilibrium input form proprioceptors in vestibular apparatus of inner ear.
47
Which pairs of cranial nerves are associated with the medulla oblongata?
Vestibulocochlear, glossopharyngeal, vagus, accessory (cranial part), and hypoglossal.
48
Pons.
Superior to medulla, and anterior to cerebellum. Works as a bridge that connects parts of the brain.
49
Ventral region of the pons.
Forms a synaptic relay station of pontine nuclei. Coordinates and maximizes the efficiency of voluntary motor movements.
50
What enters and exits the pontine nuclei?
White matter tracts, which connect one cerebral hemisphere to the opposite cerebellar hemisphere.
51
Dorsal region of the pons.
Contains ascending and descending tracts, and nuclei of cranial nerves.
52
Pontine respiratory group.
Controls breathing alongside the medullary respiratory centre.
53
Which pairs of cranial nerves are associated with the pons?
Trigeminal, abducens, facial and vestibulocochlear.
54
Midbrain.
Extends from pons to diencephalon.
55
What structure passes through the midbrain and connects the third and fourth ventricles?
Cerebral aqueduct.
56
Anterior midbrain.
Contains cerebral peduncles, and axons of the corticospinal, corticobulbar and corticopontine tracts which relay impulses from motor areas in cerebral cortex to the spinal cord, medulla and pons.
57
Posterior midbrain.
Also called the tectum. Contains 4 rounded elevations (colliculi).
58
Superior colliculi.
Two. Reflex centres for visual activities. Responsible for reflexes that govern movements of the head, eyes and trunk.
59
Inferior colliculi.
Two. Reflex centres for the startle reflex stimulated by a loud noise. Responsible for relaying impulses from auditory receptors in inner ear to brain.
60
Where is the substantial nigra, and what is its function?
Midbrain. Contains neurons that release DA for control of subconscious muscle activities. Loss of these neurons is associated with PD.
61
Where are the red nuclei, and what are their functions?
Midbrain. Axons from cerebellum and cerebral cortex form synapses in the red nuclei to control muscle activities.
62
What gives the red nuclei their colour?
Rich blood and iron supply.
63
Which pairs of cranial nerves are associated with the midbrain?
Oculomotor and trochlear.
64
Reticular formation.
Broad region where white matter and gray matter form a netlike arrangement. Extends throughout the brainstem from the spinal cord to the diencephalon.
65
Reticular activating system (RAS).
Ascending portion of the reticular formation. Sensory axons project through the thalamus to the cerebral cortex. Activated by visual, auditory, pain, touch, pressure, limb and head receptors, and mental activities.
66
What is the most important function of the RAS?
Consciousness.
67
How does RAS prevent sensory overload?
Filters out insignificant information so that it does not reach consciousness.
68
Inactivation of RAS produces:
Sleep.
69
Damage to RAS produces:
Coma.
70
Descending RAS.
Connects to cerebellum and spinal cord to regulate muscle tone, HR, BP, RR.
71
What is the second biggest structure of the brain?
Cerebellum. Contains almost half of the neurons in the brain.
72
Cerebellum.
Posterior to medulla and pons. Inferior to cerebrum. Highly folded to increase surface area of outer gray matter cortex.
73
Transverse fissure.
Deep groove that separates the cerebellum from the cerebrum.
74
Tentorium cerebelli.
Separates the cerebellum from the cerebrum, and supports the posterior cerebrum.
75
Vermis.
Medial portion of the cerebellum that connects the two hemispheres.
76
Anterior and posterior cerebellar lobes.
Involved in subconscious skeletal muscle movements.
77
Flocculondular lobe of cerebellum.
Involved in equilibrium and balance.
78
Cerebellar cortex.
Superficial layer that consists of gray matter folia. Deep to the gray matter are arbor vitae (white matter). Deeper to the gray matter are cerebellar nuclei (gray matter).
79
Cerebellar peduncles.
Bundles of white matter that attach the cerebellum to the brainstem.
80
Superior cerebellar peduncles.
Contain axons that extend from the cerebellum to red nuclei and thalamus.
81
Middle cerebellar peduncles.
Largest peduncles. Contain axons that extend from the pontine nuclei to the cerebellum for voluntary movement control.
82
Inferior cerebellar peduncles.
Contain axons of the spinocerebellar tract that extent from proprioceptors in trunk and limbs to cerebellum. Contain axons that extend from the vestibular apparatus of the inner ear and the vestibular nuclei of the medulla and pons to the cerebellum. Contain axons that extend from the inferior olivary nucleus of the medulla to the cerebellum. Contain axons that extend from the cerebellum to the vestibular nuclei of the medulla and pons. Contain axons that extend from cerebellum to reticular formation.
83
What is the main function of the cerebellum?
Coordinate movements, and regulates posture and balance.
84
Thalamus.
Major relay station of the brain. Makes up 80% of diencephalon. Consists of paired oval masses of gray matter organized into nuclei with interspersed white matter tracts.
85
Interthalamic adhesion.
A bridge of gray matter between the right and left halves of the thalamus. Present in 70% of human brains.
86
Internal medullary lamina.
Vertical Y-shaped sheet of white matter that divides the gray matter of the right and left sides of the thalamus. Consists of myelinated axons that enter and exit the thalamic nuclei.
87
Internal capsule.
Thick band of white matter lateral to the thalamus. Axons that connect thalamus to cerebral cortex pass through this structure.
88
How does the thalamus contribute to motor functions?
Relays information from cerebellum and basal nuclei to primary motor area of cerebral cortex.
89
Anterior nucleus of thalamus.
Receives input from hypothalamus and sends output to limbic system to regulate emotion and memory.
90
Medial nuclei of thalamus.
Receive input from limbic system and basal nuclei, and send output to cerebral cortex to regulate emotion, learning, memory, cognition.
91
Lateral group nuclei of thalamus.
Receive input from limbic system, superior colliculi and cerebral cortex, and send output to cerebral cortex. 1) Lateral dorsal nucleus: emotional expression. 2) Lateral posterior nucleus and pulvinar nucleus: integrates sensory information.
92
Ventral group nuclei of thalamus.
1) Ventral anterior nucleus: receives input from basal nuclei and sends output to motor areas of cerebral cortex for movement control. 2) Ventral lateral nucleus: receives input from cerebellum and basal nuclei and sends output to motor areas of cerebral cortex for movement control. 3) Ventral posterior nucleus: relays impulses for somatic sensations (touch, pressure, temperature, pain, proprioception). 4) Lateral geniculate nucleus: receives visual input from retina and sends output to primary visual area of cerebral cortex. 5) Medial geniculate nucleus: receives auditory input from ear and sends output to primary auditory area of cerebral cortex.
93
Intralaminar nuclei of thalamus.
Within medullary lamina. Make connections with reticular formation, cerebellum, basal nuclei, cerebral cortex. Function in arousal and integration of sensory and motor information.
94
Midline nucleus of thalamus.
Forms a thin band adjacent to the third ventricle. Functions in memory and olfaction.
95
Reticular nucleus of thalamus.
Surrounds lateral part of thalamus. Monitors and integrates activities of thalamic nuclei.
96
Hypothalamus.
Major regulator of homeostasis. Small region of diencephalon located inferior to the thalamus. Composed of 12 nuclei in 4 major regions.
97
Mammillary region of hypothalamus.
Adjacent to midbrain. Posterior part of hypothalamus. Consists of mammillary bodies and posterior hypothalamic nuclei.
98
Mammillary bodies.
Two small rounded projections that serve as relay station for reflexes related to smell.
99
Tuberal region of hypothalamus.
Widest part of hypothalamus. Consists of dorsomedial nucleus, ventromedial nucleus, arcuate nucleus and infundibulum.
100
Infundibulum.
Connects pituitary gland to hypothalamus. Encircled by the median eminence.
101
Supraoptic region of hypothalamus.
Superior to optic chiasm. Contains paraventricular nucleus, supraoptic nucleus, anterior hypothalamic nucleus and suprachiasmatic nucleus.
102
Preoptic region of hypothalamus.
Anterior to supraoptic region of hypothalamus. Participates with hypothalamus in regulating certain autonomic activities. Contains medial and lateral preoptic nuclei.
103
Pituitary gland.
Also called hypophysis. Projects from the hypothalamus.
104
What are the 6 functions of the hypothalamus?
1) Control of ANS. 2) Production of hormones. 3) Regulation of emotional and behavioural patterns. 4) Regulation of eating and drinking. 5) Control of body temperature. 6) Regulation of circadian rhythms.
105
How does the hypothalamus control the ANS?
Regulates HR, movement of food through GI, and contraction of urinary bladder.
106
How does the hypothalamus control hormone production?
Releasing and inhibiting hormones are released into median eminence --> blood carries them to anterior lobe of pituitary gland --> stimulate or inhibit the release of oxytocin and vasopressin (ADH) --> these hormones are transported to posterior pituitary gland for release.
107
How does the hypothalamus regulate emotional and behavioural patterns?
Works with limbs system.
108
How does the hypothalamus regulate eating and drinking?
Feeding centre, satiety centre, thirst centre.
109
How does the hypothalamus control body temperature?
Senses high temperature --> stimulates ANS to promote heat loss. Senses low temperature --> stimulates ANS to produce and retain heat.
110
How does the hypothalamus regulate circadian rhythms?
Suprachiasmatic nucleus receives input from eyes and sends output to hypothalamic nuclei, reticular formation and pineal gland.
111
What serves as the body's internal biological clock?
Suprachiasmatic nucleus of hypothalamus.
112
Epithalamus.
Superior and posterior to thalamus. Contains the pituitary gland and habenular nuclei.
113
Pineal gland.
Small pea-sized system that protrudes from the posterior midline of the third ventricle. Secretes melatonin.
114
Habenular nulei.
Involved in emotional responses to olfaction.
115
Circumventricular organs (CVOs).
Part of diencephalon, and line the walls of the third ventricle. Include part of the hypothalamus, pineal gland and pituitary gland.
116
What are the functions of the CVOs?
Monitor chemical changes in the blood since they lack a BBB, coordinate homeostatic activities of the endocrine and nervous systems, regulate BP, fluid balance hunger and thirst. Thought to be the sites of entry into the brain for HIV.
117
Cerebrum.
Seat of intelligence. Consists of outer cerebral cortex, internal cerebral white matter, and gray matter nuclei deep within the white matter. Functions in reading, writing, speaking, calculating, composing music, remembering, planning for the future, being creative.
118
Cerebral cortex.
Outer gray matter layer. Contains billions of neurons arranged in layers. Contains gyri, convolutions, fissures (deep grooves), and sulci (shallow grooves).
119
Longitudinal fissure of cerebral cortex.
Most prominent fissure. Separates cerebrum into right and left hemispheres. Holds the flax cerebri.
120
Corpus callosum of cerebral cortex.
Internally connects the cerebral hemispheres. A broad band of white matter.
121
Cerebral lobes.
Frontal, parietal, temporal, occipital.
122
Central sulcus.
Separates frontal lobe and parietal lobe.
123
Precentral gyrus.
Contains primary motor area of cerebral cortex.
124
Postcentral gyrus.
Contains primary somatosensory area of cerebral cortex.
125
Lateral cerebral sulcus.
Separates frontal lobe and temporal lobe.
126
Parietooccipital sulcus.
Separates parietal lobe and occipital lobe.
127
Insula.
Cannot be seen at surface since it lies within the lateral cerebral sulcus.
128
Cerebral white matter.
Consists of myelinated axons in 3 types of tracts: 1) Association tracts. 2) Commissural tracts. 3) Projection tracts.
129
Association tracts.
Contain axons that conduct impulses between gyri in the same cerebral hemisphere.
130
Commissural tracts.
Contain axons that conduct impulses from gyri in one cerebral hemisphere to corresponding gyri in the other cerebral hemisphere. Examples: corpus callosum, anterior commissure, posterior commissure.
131
Projection tracts.
Contain axons that conduct impulses from the cerebrum to lower parts of the CNS, or from lower parts of the CNS to the cerebrum.
132
Basal nuclei.
Each cerebral hemisphere has 3 nuclei collectively termed the basal nuclei.
133
Globus pallidus and putamen.
Two basal nuclei that lie side by side lateral to the thalamus. Together, they are named the lentiform nucleus. Globus pallidus regulates muscle tone, and putamen anticipates body movements.
134
Caudate nucleus.
The third basal nuclei. Large head and small tail.
135
Corpus striatum.
Lentiform nucleus and caudate nucleus together.
136
Claustrum.
Thin sheet of gray matter lateral to the putamen. Subdivision of basal nuclei.
137
The basal nuclei receive input from the cerebral cortex and provide output to motor areas of the cortex via:
Medial and ventral group nuclei of the thalamus.
138
What are the functions of the basal nuclei?
Initiate and terminate movements, control subconscious contractions of skeletal muscles, initiate and terminate attention, memory, planning, and regulate emotional behaviours alongside limbic system.
139
Limbic system.
Consists of the limbic lobe, dentate gyrus, amygdala, septal nuclei and mammillary bodies of hypothalamus.
140
Limbic lobe.
Rim of cerebral cortex on medial surface of each cerebral hemisphere. Includes cingulate gyrus and parahippocampal gyrus.
141
Dentate gyrus.
Between hippocampus and parahippocampal gyrus.
142
Amygdala.
Composed of groups of neurons located close to the tail of the caudate nucleus.
143
Septal nuclei.
Within septal area formed by regions under the corpus callosum and paraterminal gyrus.
144
Which nuclei of the thalamus participate in limbic circuits?
Anterior nucleus and medial nucleus.
145
Sensory areas of cerebral cortex.
Primary somatosensory area, primary visual area, primary auditory area, primary gustatory area, primary olfactory area.
146
Sensory impulses arrive in what area of the cerebral hemispheres?
Posterior half.
147
Primary somatosensory area.
Posterior to central sulcus of each cerebral hemisphere in post central gyrus of each parietal lobe. Receives impulses for touch, pressure, vibration, itch, tickle, temperature, pain, proprioception. Contains sensory homunculus.
148
Primary visual area.
Posterior tip of occipital lobe. Receives visual information for visual perception.
149
Primary auditory area.
Superior part of temporal lobe. Receives sound information for auditory perception.
150
Primary gustatory area.
Located in insula. Receives taste information for gustatory perception and taste discrimination.
151
Primary olfactory area.
Located in temporal lobe. Receives smell information for olfactory perception.
152
Motor areas of cerebral cortex.
Primary motor area and Broca's speech area.
153
Motor output from the cerebral cortex flows from which part of each hemisphere?
Anterior part.
154
Primary motor area.
Located in precentral gyrus of frontal lobe. Contains motor homunculus.
155
Broca's speech area.
Located in frontal lobe. Impulses pass from Broca's speech area to premotor regions that control speech muscles.
156
Association areas of cerebral cortex.
Somatosensory association area, visual association area, facial recognition area, auditory association area, orbitofrontal cortex, Wernicke's area, common integrative area, prefrontal cortex, premotor area, frontal eye field area.
157
What connects the association areas of the cerebral cortex?
Association tracts.
158
Somatosensory association area.
Posterior to primary somatosensory area. Receives input from primary somatosensory area and thalamus. Functions in determining shape and texture of objects, determining object orientation, sensing body orientation, and memory storage of past somatic sensory experiences.
159
Visual association area.
Located in occipital lobe. Receives impulses from primary visual area and thalamus, and relates present and past visual experiences. Responsible for recognizing and evaluating visual experiences.
160
Facial recognition area.
Located in inferior temporal lobe. Receives impulses from visual associated area. More dominant in right hemisphere.
161
Auditory association area.
Inferior and posterior to primary auditory area in temporal cortex. Allows you to recognize a sound as speech, music or noise.
162
Orbitofrontal cortex.
Receives input from primary olfactory area. Allows you to identify smells. More dominant in right hemisphere.
163
Wernicke's area.
Posterior language area in temporal and parietal lobes. Interprets meaning of speech by recognizing spoken words.
164
Common integrative area.
Receives input from somatosensory association area, visual association area, auditory association area, primary gustatory area, primary olfactory area, thalamus and brainstem. Functions in thought formation.
165
Prefrontal cortex.
Frontal association area. Functions in personality, intellect, learning abilities, information recall, initiative, judgement, foresight, reasoning, conscience, intuition, mood and planning.
166
Premotor area.
Motor association area. Located anterior to primary motor area. Functions in storing learned muscle movements. Generates impulses that cause specific groups of muscles to contract.
167
Frontal eye field area.
Controls voluntary scanning movements of the eyes.
168
Hemispheric lateralization.
Functional asymmetry between the right and left sides of the brain.
169
Alpha waves.
8-13 Hz. Present in ECGs of all normal individuals when they are awake and resting with eyes closed. Disappear during sleep.
170
Beta waves.
14-30 Hz. Appear when the nervous system is active.
171
Theta waves.
4-7 Hz. Occur in children and adults experiencing emotional stress.
172
Delta waves.
1-5 Hz. Occur in sleeping adults and awake infants.
173
Which brain wave indicates brain damage in an awake adult?
Delta waves.
174
Special sensory nerves.
Olfactory, optic, vestibulocochlear.
175
Motor nerves.
Oculomotor, trochlear, abducens, accessory, hypoglossal.
176
Branchial motor axons.
Innervate skeletal muscles that develop from the pharyngeal arches. Leave the brain through mixed cranial nerves and the accessory nerve.
177
Somatic motor axons.
Innervate skeletal muscles that develop from head somites (eye and tongue muscles). Leave the brain through 5 motor cranial nerves.
178
Mixed nerves.
Trigeminal, facial, glossopharyngeal, vagus.
179
Olfactory nerve.
(I). Involved in olfaction.
180
What are the olfactory receptors?
Bipolar neurons within the olfactory epithelium. Each has a single odor-sensitive dendrite projecting from one side of the cell body, and an unmyelinated axon extending from the other side.
181
What forms the olfactory nerves?
Bundles of axons of olfactory receptors extend through 20 olfactory foramina in the cribriform plate of the ethmoid bone on each side of the nose.
182
Olfactory bulbs.
Where olfactory nerves end. Two extensions of the brain that rest on the cribriform plate. Within the olfactory bulbs, olfactory tracts extend posteriorly and end in the primary olfactory area in the temporal lobe.
183
Optic nerve.
(II). Involved in vision. Technically a tract of the brain.
184
Describe the propagation of visual signals.
Rods and cones in the retina initiate visual signals --> to bipolar cells --> to ganglion cells --> axons join to form optic nerve --> passes through optic foramen.
185
Optic chiasm.
Where the two optic nerves merge. Axons from the medial half of each eye cross to the opposite side, and axons from the lateral half remain on the same side.
186
Optic tracts.
The regrouped axons after the optic chiasm form the optic tracts.
187
Oculomotor nerve.
(III). Involved in eyeball and upper eyelid movement.
188
Describe the sensory axons of the oculomotor nerve.
They do not return to the brain. The cell bodies reside in the mesencephalic nucleus and enter the midbrain via the trigeminal nerve.
189
Describe the motor nucleus of the oculomotor nerve.
Located in anterior midbrain. Extends anteriorly and divides into superior and inferior branches which pass through the superior orbital fissure into the orbit.
190
Superior branch of the oculomotor nerve.
Innervates superior rectus muscles and levator palpebral superiors muscle.
191
Inferior branch of the oculomotor nerve.
Innervates medial rectus muscle, inferior rectus muscle, inferior oblique muscle, and parasympathetic motor axons to intrinsic eyeball muscles (smooth muscle).
192
Trochlear nerve.
(IV). Smallest cranial nerve. The only cranial nerve that arises from the posterior brainstem. Involved in eyeball movement.
193
Describe the sensory axons of the trochlear nerve.
They do not return to the brain. The cell bodies reside in the mesencephalic nucleus and enter the midbrain via the trigeminal nerve.
194
Describe the motor neurons of the trochlear nerve.
Somatic motor neurons originate in trochlear nucleus --> axons cross to opposite side of brain --> wrap around pons --> exit through superior orbital fissure into orbit --> innervate superior oblique muscle.
195
Trigeminal nerve.
(V). Largest cranial nerve. Emerges from two roots on the anterolateral surface of the pons. Involved in touch, pain and thermal sensations.
196
What are the 3 branches of the trigeminal nerve?
Ophthalmic nerve, maxillary nerve, mandibular nerve.
197
Ophthalmic nerve.
Smallest branch of trigeminal nerve. Passes into orbit via superior orbital fissure. Innervates the cornea, upper eyelid, lacrimal glands, upper nasal cavity, side of nose, forehead, and anterior half of scalp.
198
Maxillary nerve.
Passes through foramen rotundum. Innervates upper jawbone, nose mucosa, palate, part of pharynx, upper teeth, upper lip and lower eyelid.
199
Mandibular nerve.
Largest branch of trigeminal nerve. Passes through the foramen oval. Innervates lower jawbone, anterior tongue (not taste), cheek, mucosa, lower teeth, side of head anterior to ear, and floor of mouth.
200
Describe the sensory axons of the trigeminal nerve.
The sensory axons from the 3 branches enter the trigeminal ganglion and terminate in nuclei in the pons. The trigeminal nerve also contains sensory axons from proprioceptors in the muscles of mastication and extrinsic muscles of the eyeball.
201
Abducens nerve.
(VI). Involved in eyeball abduction. Innervates the lateral rectus muscle.
202
Describe the sensory axons of the abducens nerve.
They do not return to the brain. The cell bodies reside in the mesencephalic nucleus and enter the midbrain via the trigeminal nerve.
203
Facial nerve.
(VII). Involved in touch, pain, thermal sensations, proprioception, saliva secretion, facial expressions. Innervates more named muscles than any other nerve, such as middle ear muscles, facial muscles, scalp muscles, neck muscles, and skin in ear canal.
204
Describe the sensory axons of the facial nerve.
Sensory axons extend from taste buds of anterior 2/3 of tongue --> enter temporal bone to join facial nerve --> to geniculate ganglion --> ends in ponds --> thalamus --> gustatory area of cerebral cortex.
205
Vestibulocochlear nerve.
(VIII). Involved in modulating hair cells in the inner ear.
206
Vestibular branch of vestibulocochlear nerve.
Extends from semicircular canals, saccule and utricle of inner ear to the vestibular ganglion for equilibrium.
207
Cochlear branch of vestibulocochlear near.
Extends from spinal organ in cochlea and carries impulses for hearing.
208
Glossopharyngeal nerve.
(IX). Involved in touch, pain, thermal sensations, proprioception and taste.
209
Describe the sensory axons of the glossopharyngeal nerve.
Sensory axons arise from taste buds on posterior 1/3 of tongue, proprioceptors of swallowing muscles, baroreceptors in carotid sinus that monitor BP, chemoreceptors in carotid bodies near carotid arteries, and external ear.
210
Where are the cell bodies of the glossopharyngeal nerve.
Superior and inferior ganglia.
211
Vagus nerve.
(X). Involved in taste, touch, pain, thermal sensations, proprioception, swallowing, vocalizing, coughing.
212
Describe the sensory axons of the vagus nerve.
Arise from the skin of external ear, taste buds in epiglottis and pharynx, proprioceptors in neck and throat muscles.
213
Describe the motor neuron of the vagus nerve.
Axons of parasympathetic motor neurons innervate the lungs, heart, glands of GI, smooth muscle of respiratory passageways, esophagus, stomach, gallbladder, small intestine, most of large intestine.
214
Where are the cell bodies of the vagus nerve?
Superior and inferior ganglia.
215
Accessory nerve.
(XI). Cranial accessory nerve is part of the vagus nerve. Spinal accessory nerve arises in anterior gray horn of C1-C5. Innervates sternocleidomastoid and trapezius to coordinate head movements.
216
Hypoglossal nerve.
(XII). Involved in tongue movement for speech and swallowing.
217
Describe the sensory axons of the hypoglossal nerve.
Sensory axons do not return to the brain. The sensory axons that originate from proprioceptors in the tongue muscles travel toward the brain in the hypoglossal nerve and then leave the nerve to join the cervical spinal nerve and end in medulla oblongata.
218
Describe the motor axons of the hypoglossal nerve.
Originate in hypoglossal nucleus --> exit medulla on anterior surface --> pass through hypoglossal canal --> tongue muscles.
