Midbrain 1 (CN 4) Flashcards
what are the bondaries of the midbrain
caudal: anterior pontine protuberance o the point behind the inf colliculus
rostral: behind (caudal to) mammillary body to post commissure
what is in the cerebral peduncle
tegmentum +
crus cerebri
what is the roof (behind/dorsal) of the cerebral aqueduct
tectum aka quadrigeminal plate bc it has 4 colliculi (bumps)
what are the superior colliculi used for
what are inf colliculi used for
sup: relay stations for vision-related info
inf: relay stations for auditory info
what is the floor of the cerebral aqueduct
what does it contain
tegmentum
-contains CN nuclei, long tracts, and reticular formation
what is the ventral part of the midbrain
what is the ventral midline of the midbrain? what CN exits here
crus cerebri
interpeduncular (cistern) fossa - CN 3 exits
where does CN 4 decussate and where does it exit
what level is the CN 4 nuclues found at?
decussates in the ant medullary vellum and exits dorsally into the ambient cistern
-at the level of the inf colliculus
what level is CN 3 nuclear complex found at
-how does it exit
at the level of the supeiror colliculus
-exits ventrally in the interpeduncular fossa
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?
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
what are locus ceruleus responsible for
norepinephrine factory
- responsible for synthesizing norepinephrine in the brain
- norep: a nt important for sympathetic responses
what neighborhoods do CN 4 pass before reaching the superior oblique muscle
- brainstem
- subarachnoid psace
- cavernous sinus
- orbit
horner’s syndrome is always _____ to the lesion
ipsilateral**
- bc that pathway never crosses
- ALWAYS TELLS YOU WAHT SIDE OF THE BODY THE LESION IS ON
what happens when the lesion is at the decussation in the ant medullary vellum
bilateral CN 4 palsy
-right AND Left CN 4
what happens when you have a lesion at the CN 4 nuclues (and locus ceruleus)
ipsi horners w/ contra CN 4 palsy
what can happen when you have a pineal gland tumor (pinealoma)
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)
what 2 arteries do CN 4 and CN 3 run between
posterior cerebral artery (PCA)
sup cerebellar artery
which CNs are in the Cavernous sinus
what artery is in the cav sinus
3, 4, 6, V1, V2
ICA
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
cavernous sinus
brainstem
-both scenarios locate the lesion to the same side as horner’s though
how does CN4 enter the orbit
from here, the nerve crosses medially over the _____ and ____ before entering the belly of the sup oblique muscle
through sup orbital fissure, outside the tendinous annulus of zinn
-levator palpebrae superioris and sup rectus msucles
- CN 4 is the only CN to exit ______
- the only CN to totally _____ after it leaves the nucleus
- exit dorsally
- to totally cross after it leaves its nucleus
the “tiny trochlear” is small and delicate and prone to damage in trauma, esp as it travels in the …..
ambient cistern along the tentorial margin
