Brainstem, Cerebellum, & Cranial Nerves

Question 1

What is located just below the brainstrem? Just above it?

Answer 1

• just below is the spinal cord!

- just above is the thalamus of the forebrain

Question 2

What are the major parts of the ventral midbrain?

Answer 2

• the cerebral peduncles (with the optic tracts crossing these to form the optic chiasm)
• (substantia nigra)
• mamillary bodies
• tuber cinereum and infundibular stalk (for the pituitary gland)
• CNs III (IV emerges from dorsal side)

Question 3

What are the major parts of the ventral pons?

Answer 3

• the basilar groove (where the basilar artery lies)

- CNs V, (VI, VII, VIII emerge at the ponto-medullary junction)

Question 4

What are the major parts of the ventral medulla?

Answer 4

• the anterior median fissure with the bilateral pyramids and olives
• CNs (VI, VII, VIII from the ponto-medullary junction) IX, X, XI, XII

Question 5

What are the major parts of the dorsal brainstem?

Answer 5

• superior and inferior colliculi (corpora quadrigemina) from the midbrain (note that the pineal gland is just superior/in between the superior colliculi)
• superior (from midbrain), middle (from pons), and inferior (from medulla) cerebellar peduncles
• dorsal median sulcus with gracile tubercle and cuneate tubercle (medulla)

Question 6

What separates the cerebrum from the cerebellum?

Answer 6

• the tentorium dural fold

Question 7

What are the major parts of the cerebellum?

Answer 7

• the median vermis, paravermal areas, and lateral cerebeller hemispheres

Question 8

What is the arbor vitae?

Answer 8

• the “tree of life”

- it is the complex of white matter found in the cerebellum

Question 9

What are the folds in the cerebellar cortex called? What separates these folds?

Answer 9

• folds: folia (NOT gyri)

- separated by fissures (NOT sulci)

Question 10

What major fissure divides each cerebellar hemisphere into an anterior and posterior lobe?

Answer 10

• the primary fissure

Question 11

Which two important structures are found on the ventral surface of the cerebellum?

Answer 11

• the flocculonodular lobe between the anterior and posterior lobe
• the cerebellar tonsils of the posterior lobe (tonsils are prone to herniation)

Question 12

Name the twelve cranial nerves.

Answer 12

• olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal

Question 13

Which cranial nerves are entirely sensory? Which are entirely motor? Which are both? Which carry parasympatethic fibers?

Answer 13

• sensory: I, II, VIII
• motor: III, IV, VI, XI, XII
• both: V, VII, IX, X
• “some say marry money, but my brother says big boobs matter most”
• parasympathetic activity: III, VII, IX, X

Question 14

Where do cranial nerves I, II, III, IV, V, and VI transit the skull?

Answer 14

• I: cribriform plate of ethmoid
• II: optic canal of sphenoid
• III: superior orbital fissure
• IV: superior orbital fissure
• V: superior orbital fissure (V1), foramen rotundum (V2), foramen ovale (V3)
• VI: superior orbital fissure

Question 15

Where do cranial nerves VII, VIII, IX, X, XI, and XII transit the skull?

Answer 15

• VII: internal auditory meatus (and then exits the skull via the stylomastoid foramen)
• VIII: internal auditory meatus
• IX: jugular foramen
• X: jugular foramen
• XI: jugular foramen
• XII: hypoglossal canal

Question 16

What accompanies the optic nerve through the optic canal?

Answer 16

• the ophthalmic artery
• (note that the central retinal branch of this artery actually enters the optic nerve, entering the eye with the nerve via the optic disc)

Question 17

Parasympathetic input to the pupils results in what? What about sympathetic input?

Answer 17

• parasympathetic (via CN III and the ciliary ganglion): constriction
• sympathetic (via cervical trunk): dilation

Question 18

Oculomotor Nerve

Answer 18

• CN III
• emerges from the ventral midbrain
• passes through the cavernous sinus and then branches, entering the superior orbital fissure as a superior and inferior branch
• damage: drooping eyelid, dilated pupil, diplopia, inability to move eye in certain directions

Question 19

Trochlear Nerve

Answer 19

• CN IV
• emerges from the DORSAL midbrain just caudal to the inferior colliculus
• passes through the cavernous sinus and enters the superior orbital fissure
• supplies the superior oblique muscle

Question 20

Trigeminal Nerve

Answer 20

• CN V
• emerges from the ventral pons as a small motor root and large sensory root
• sensory root forms the large trigeminal ganglion, from which emerge V1 (ophthalmic; through superior orbital fissure), V2 (maxillary; through foramen rotundum), and V3 (mandibular; through foramen ovale) divisions
• the motor root skips the ganglion and then merges with V3 (V1 and V2 are therefore strictly sensory)

Question 21

What are the major clinically important branches of V3?

Answer 21

• (V3 = mandibular branch of trigeminal nerve)
• inferior alveolar nerve (sensory to mandible, lower teeth, and overlying skin)
• nerve to mylohyoid (branches from the inferior alveolar nerve to supply the muscles of the floor of the mouth)
• lingual nerve (general sensation to anterior 2/3 of tongue - NOT taste)

Question 22

What supplies the general sensation and the special taste sensation of the tongue?

Answer 22

• anterior 2/3: the chorda tympani branch of the facial nerve supplies taste; lingual nerve (branch of trigeminal nerve V3) supplies general sensation
• posterior 1/3: general sensation and taste provided by the glossopharyngeal nerve

Question 23

Abducens Nerve

Answer 23

• CN VI
• arises from the ventral groove between the pons and medulla
• travels through the cavernous sinus and through the superior orbital fissure
• supplies the lateral rectus muscle

Question 24

Facial Nerve

Answer 24

• CN VII
• arises from the ventral groove between the pons and medulla
• emerges as two roots: the main motor root and the nervus intermedius (taste senesory and parasympathetic; lies inbetween the main motor root and CN VIII); both roots enter the internal acoustic meatus and then merge into a single nerve
• passes into the facial canal, forms the geniculate ganglion, greater petrosal nerve branch, nerve to stapedius muscle, and then chorda tympani before exiting via the stylomastoid foramen
• once out, it gives off several more branches to supply facial muscles

Question 25

What is the geniculate ganglion? The greater petrosal nerve? The chorda tympani?

Answer 25

- these are all structures arisnig from the facial nerve - geniculate ganglion contains primary sensory cells of taste - greater petrosal nerve contains parasympathetic fibers - chorda tympani joins the lingual nerve of V3 to supply the anterior 2/3 of tongue with taste sensation

Question 26

What are the five main trunks of the facial nerve that arise once the nerve leaves the stylomastoid foramen?

Answer 26

- (these supply the facial muscles) - TZBMC: temporal, zygomatic, buccal, mandibular, cervical - (also have the posterior auricular)

Question 27

Vestibulocochlear Nerve

Answer 27

- CN VIII - emerges from the ventral groove between pons and medulla (immediately lateral to the nervus intermedius of CN VII) - contains the vestibular (balance sensation) and cochlear (aduitory sensation) nerves; these branch from the main nerve body once it passes through the internal acoustic meatus - *it does not leave the skull*

Question 28

Glossopharyngeal Nerve

Answer 28

- CN IX - emerges from the ventral medulla (between the olive and the inferior cerebellar peduncle) and leaves the skull via the jugular foramen

Question 29

Vagus Nerve

Answer 29

- CN X - emerges from the ventral medulla (between the olive and the inferior cerebellar peduncle) and leaves the skull via the jugular foramen (it forms a superior ganglion before leaving and an inferior ganglion once it leaves) - in the neck, it lies in the carotid sheath (with the carotid arteries and internal jugular vein) and gives off the superior laryngeal nerve and then the recurrent laryngeal nerve

Question 30

Accessory Nerve

Answer 30

- CN XI - composed of a cranial root and spinal accessory root - cranial root emerges from the ventral medulla (between the olive and the inferior cerebellar peduncle) - spinal root is formed by C1-C5 and enters the foramen magnum - the two join together and then leave via the jugular foramen - spinal fibers innervate trapezius and sternocleidomastoid; cranial innervate pharyngeal muscles

Question 31

What joins the inferior vagal ganglion?

Answer 31

- (this ganglion forms after the vagus nerve emerges from the jugular foramen) - it is joined by the accessory nerve's spinal fibers to be distributed to the pharyngeal muscles

Question 32

Hypoglossal Nerve

Answer 32

- CN XII | - emerges from the ventral medulla between the pyramid and olive and leaves via the hypoglossal canal

Question 33

What joins the hypoglossal nerve? What is the ansa cervicalis

Answer 33

- motor fibers from the upper 2 or 3 cervical spinal nerves join the hypoglossal nerve and then leave it to form a loop of nerves called the ansa cervicalis