Oculomotor System II VOR

Question 1

How do you get different eye movements by using different extraocular muscles?

Answer 1

Get them to cancel out.

Eg,
- get torsion components to cancel out if you want just elevation.
- if you want just intorsion and no elevation no depression, make these cancel out

This is how you do this by using multiple muscles at once

Question 2

What components do each of these have:

burst neuron, motor neuron, tonic neuron

Answer 2

Motor neuron: both

Tonic neuron: only step component

Burst neuron: only pulse component

Question 3

how do you get eye velocity from head velocity?

Answer 3

head velocity (H dot) x (-1) = eye velocity (E dot)

You want the eye velocity to be equal and opposite the head velocity so the movement in space is 0. you can do this by:
- going through an inhibitory synapse
- cross the midline

Question 4

What is the structure of the vestibular apparatus?

Answer 4

3 semicircular canals. “the labyrinth”

Question 5

How are the 3 semicircular canals functionally organized in the vestibular apparatus?

Answer 5

• organized into three orthogonal planes
• theres fluid in the left and right horizontal canals that when we moves takes this inertia

Left and right canals are on top of the head, posterior and anterior.
- left anterior and right posterior are in the same plane, right anterior and left posterior are in the same plane

Question 6

Describe how the vestibular hair cell and afferent response works

Answer 6

Opponent processing: afferent has resting discharge and can therefore signal both directions of head motion via increase or decrease in activity
- at rest, no hair cell is moving, result is that the primary afferent has a discharge rate (resting discharge). this means that when the hair is bent one way it depolarizes, increase in discharge rate. But in the other canal, where the hair cell is bent the opposite direction there is a hyperpolarization, decrease in discharge rate

Question 7

moving your head to the right, which muscles involved and how:

lateral and medial rectus of each eye

Answer 7

moving to the right,
right eye:
- lateral rectus active pulling,
- medial rectus (antagonist) lets go

left eye:
- medial rectus active pulling
- lateral rectus (antagonist) lets go

Question 8

Describe the plasticity in VOR

Answer 8

Extrastriate visual cortex –> pontine nuclei –> cerebellum (plasticity, motor learning) teaching to vestibular nucleus (pons-medulla)

the cerebellum is critical for plasticity and motor learning
- this reflex needs to be very efficient and accurate. Vestibular input also goes up to the cerebellum from both the horizontal canal and the vestibular nucleus. The extrastriate visual cortex projects into the pontine nucleus, and delivers this visual signal
- when the signal is not 0, the reflex wasn’t optimized, so something doesn’t match. so there is a teaching signal sent out to tweak the gain on the synapses of the vestibular nucleus. any behaviours where you’re moving your head and your eyes are doing something and the reflex didn’t work properly this happens

Question 9

Motor neurons carry a pulse, related to ___________, and step, related to ___________

Answer 9

Motor neurons carry a pulse, related to eye velocity (move the eye)
, and step, related to eye position (maintain force so the eye stays there)