Midbrain 1 (CN 4)

Question 1

what are the bondaries of the midbrain

Answer 1

caudal: anterior pontine protuberance o the point behind the inf colliculus
rostral: behind (caudal to) mammillary body to post commissure

Question 2

what is in the cerebral peduncle

Answer 2

tegmentum +

crus cerebri

Question 3

what is the roof (behind/dorsal) of the cerebral aqueduct

Answer 3

tectum aka quadrigeminal plate bc it has 4 colliculi (bumps)

Question 4

what are the superior colliculi used for

what are inf colliculi used for

Answer 4

sup: relay stations for vision-related info
inf: relay stations for auditory info

Question 5

what is the floor of the cerebral aqueduct

what does it contain

Answer 5

tegmentum

-contains CN nuclei, long tracts, and reticular formation

Question 6

what is the ventral part of the midbrain

what is the ventral midline of the midbrain? what CN exits here

Answer 6

crus cerebri

interpeduncular (cistern) fossa - CN 3 exits

Question 7

where does CN 4 decussate and where does it exit

what level is the CN 4 nuclues found at?

Answer 7

decussates in the ant medullary vellum and exits dorsally into the ambient cistern
-at the level of the inf colliculus

Question 8

what level is CN 3 nuclear complex found at

-how does it exit

Answer 8

at the level of the supeiror colliculus

-exits ventrally in the interpeduncular fossa

Question 9

what kind of relay station are inf colliculi?
where do the inf colliculi recieve info from
after synapsing at the inf colliculi, wehre do the auditory pathway fibers continue to synapse at?

Answer 9

auditory relay stations
the lateral lemniscus
-auditory pathway fibers in the lateral lem are headed to the nucleus of the inf colliculus, wehre they will synapse
-after synapsing there, the pathway continues north to synapse at the medial geniculate body of the thalamus

Question 10

what are locus ceruleus responsible for

Answer 10

norepinephrine factory

• responsible for synthesizing norepinephrine in the brain
• norep: a nt important for sympathetic responses

Question 11

what neighborhoods do CN 4 pass before reaching the superior oblique muscle

Answer 11

1. brainstem
2. subarachnoid psace
3. cavernous sinus
4. orbit

Question 12

horner’s syndrome is always _____ to the lesion

Answer 12

ipsilateral**

• bc that pathway never crosses
• ALWAYS TELLS YOU WAHT SIDE OF THE BODY THE LESION IS ON

Question 13

what happens when the lesion is at the decussation in the ant medullary vellum

Answer 13

bilateral CN 4 palsy

-right AND Left CN 4

Question 14

what happens when you have a lesion at the CN 4 nuclues (and locus ceruleus)

Answer 14

ipsi horners w/ contra CN 4 palsy

Question 15

what can happen when you have a pineal gland tumor (pinealoma)

Answer 15

can compress the decussating CN 4 fibers and cause bilateral CN 4 palsy to the ant medullary vellum
-look for dorsal midbrain syndrome (tectal pupils, upgaze paralysis, lid retraction, convergence retraction nystagmus)

Question 16

what 2 arteries do CN 4 and CN 3 run between

Answer 16

posterior cerebral artery (PCA)

sup cerebellar artery

Question 17

which CNs are in the Cavernous sinus

what artery is in the cav sinus

Answer 17

3, 4, 6, V1, V2

ICA

Question 18

if you have horner’s syndrome on the same side as the CN 4 palsy, where is the lesion?

if you have horner’s syndrome on the opp side as the CN 4 palsy, where is the lesion

Answer 18

cavernous sinus

brainstem

-both scenarios locate the lesion to the same side as horner’s though

Question 19

how does CN4 enter the orbit

from here, the nerve crosses medially over the _____ and ____ before entering the belly of the sup oblique muscle

Answer 19

through sup orbital fissure, outside the tendinous annulus of zinn
-levator palpebrae superioris and sup rectus msucles

Question 20

• CN 4 is the only CN to exit ______

- the only CN to totally _____ after it leaves the nucleus

Answer 20

• exit dorsally

- to totally cross after it leaves its nucleus

Question 21

the “tiny trochlear” is small and delicate and prone to damage in trauma, esp as it travels in the …..

Answer 21

ambient cistern along the tentorial margin