Midbrain 2-Mesencephalic-diencephalic junction

Question 1

wehre do auditory fibers in the brachium of the inf colliculus synpase on

Answer 1

the medial geniculate (of the thalmus)

Question 2

where do the optic tract fibers synapse

Answer 2

1. some optic tract fibers (ex. visual field fibers) are heading to the lateral geniculate to synpase
2. other optic tract fibers (ex. pupillary light reflex) head to the pretectal area to synapse
   - via the brachium of sup colliculus

Question 3

do pupillary light reflex fibers synapse on the LGN?

Answer 3

no.
- the afferent limb of the pupillary light reflex does NOT synapse at the thalamus
- use brachium of the sup colliculus to bypass LGN and instead head to the pretectal area (1st synapse)

Question 4

most sensory info trying ot get ot higher-level cerebral cortex needs to synpase in _____ before being allowed entry

Answer 4

thalamus

Question 5

what is the first synapse in the pupillary light reflex

Answer 5

pretectal olivary nucleus

Question 6

which nuclei are important for vertical gaze

Answer 6

MLF, nucleus of Darkschewitsch, intersitital nucleus of cajal (INC)

Question 7

what are M-group and NPC (nucleus of post commisure) important for

Answer 7

important to coordinate lids w/ vertical gaze

Question 8

what is INC (interstitial nucleus of Cajal) importnat for

Answer 8

vertical gaze holding

Question 9

hat is riMLF used for

Answer 9

contains “burst neurons” for generating both downward and upward saccades

Question 10

what is the goal of pupil info

Answer 10

to synapse on EW

Question 11

where does the afferent limb of the pupillary light reflex synapse on
-then what happens

Answer 11

pretectal nuclei
-then some interneurons cross in the post commissure (some stay uncrossed) to synapse on EW subnucleus, which is just one level down

Question 12

why can a lesion in the nervous system specifically damage the light pathway while leaving the near pathway preserved

Answer 12

the near pathway sneaks in by projecting to an ill defined ventrally placed area and on to the 3rd nerves

called light-near dissociation

Question 13

why is the near response virtually always normal with a normal light reaction

Answer 13

bc of the 30:1 ratio

~94% of the parasympathetic fibers coming out of the EW nucleus are dedicated to the near triad and ~6% to light pathway

Question 14

what does the swinging light test specifically compare

Answer 14

the one afferent limb to the other

Question 15

what are the 5 causes of light-near dissociation

Answer 15

1. blind
2. tectal (DMS)
3. argyll robertson
4. aberrant regeneration of CN 3
5. tonic

Question 16

why can the axons of the CNS not completely regenerate?

Answer 16

partly bc of the large glial scar that forms after injury

-scar impedes growth factors meant to help new axon sprouts from finding their target

Question 17

why is CN2 considered CNS

Answer 17

bc it develops from and projects to the diencephalon

assosicated w/ oligodendrocytes rather than schwann cells

Question 18

wwhat are some examples that could happen in aberrant regeneration of CN 3

Answer 18

1. miosis in adduction or depression
2. elevation of the ptotic eye in adduction or depression
3. light-near dissociation

Question 19

why do you get light near dissociation in tonic pupils

Answer 19

due to a lesion at the ciliary ganglion (or short ciliary nerves)

• 90% of fibers arising from CG are destined for the ciliary body to aid in acc and the near triad w/ only 10% for sphincter so it has a greater chnace of impoariing pupillary constriction to light than that ass w/ acc
• after being injred, the chances that new axons that sprout or regenerate will be those near fibers that will come back and re-supply the pupil instead
• “aberrant regneration” of CB fibersto the iris spincter

Question 20

what are the CN used to move the eyes

Answer 20

3, 4, 6

Question 21

from brainstem origin to target, what are the CN course called

Answer 21

infranuclear