Vestibular and Occulomotor Systems

Question 1

What is smooth pursuit? When can/can’t you do it?

Answer 1

Smoothly following a moving object. Can’t be done voluntarily in the absence of a moving object.

Question 2

What’s the VOR?

Answer 2

Vestibular-Occular Reflex - keeps your gaze steady even when turning / changing the angle of the head.

Question 3

What are optokinetic movements?

Answer 3

Movement reflexively generated when a large portion of the visual field moves slowly… like being on a train….

Question 4

What are saccades?

Answer 4

Rapid eye movement when shifting fixation from one object to another.

Question 5

What is vergence? What makes this different from other eye movements?

Answer 5

In vergence, eyes move in opposite directions to focus on near object (convergence) or far objects (divergence). Other eye movements have eyes “yolked,” moving in the same direction.

Question 6

What are fixation movements? Are they voluntary or involuntary?

Answer 6

Small, rapid, conjugate movements of the eyes when fixating at an object. Involuntary. Necessary to maintain the image.

Question 7

Are there stretch reflexes involving the muscles of the eye?

Answer 7

Nope.

Question 8

Review: At what level is the abducens nucleus?

Answer 8

At the pontomedullary junction.

Question 9

Review: At what level is the trochlear nucleus?

Answer 9

At the inferior colliculus.

Question 10

Review: At what level is the occulomotor nucleus?

Answer 10

Just about at the superior colliculus.

Question 11

What 2 forces must be overcome to move the eye?

Answer 11

Elastic restoring force (proportional to distance) and viscous resistance (proportional to velocity)

Question 12

What is the pulse-step concept for eye movment?

Answer 12

Muscles moving the eye fire in bursts, the “pulse,” to initially displace the eye. The “step” is the tonic contraction that keeps the eye in place despite elastic restoring force.

Question 13

What are the 2 places in the brain that produce eye movement?

Answer 13

The frontal eye field (FEF) and superior coliculus.

Question 14

What kind of stimulus does the superior coliculus generate saccades in response to?

Answer 14

Unexpected, fast visual (and auditory??) stimuli - the professor banged on the podium to try to evoke such a response.

Question 15

What is the PPRF?

Answer 15

Paramedian pontine reticular formation. Set of interneurons near abducens nucleus that generates pulse.

Question 16

What is the “integrator”?

Answer 16

Structure that generates the “step” to sustain muscle contraction.

Question 17

Are the PPRF and integrator upstream or downstream of the MLF?

Answer 17

Upstream of the MLF.

Question 18

Where do the cell bodies carrying vestibular information in the CN VIII live?

Answer 18

In Scarpa’s ganglion

Question 19

What kind of cells detect linear acceleration? What structures are involved?

Answer 19

Hair cells - they detect movement of otoconia (calcium carbonate rocks) on the otolithic membrane.

Question 20

Describe how the vestibular system detects changes in head angle.

Answer 20

Head movement moves endolymph, which causes displacement of the cupula, which bends hair cells.

Question 21

Which side of the canal has hair cells that increase signaling when the head is tilting?

Answer 21

Hair cells on the side toward which the head is rotating.

Question 22

What’s the relationship between semicircular canal signaling, head angular acceleration, and head angular velocity.

Answer 22

Signaling is proportional to velocity, but only occurs when the acceleration is non-zero.

Question 23

What is nystagmus? What’s the naming convention in terms of left-beating or right-beating?

Answer 23

Eyes snapping back to fixation point. A left-beating nystagmus means that… the eyes have snapped back to the left after the eyes were slowing tracking to the right to compensate for the head being turned to the left. (this… like many concepts presented by Dr. Palmer, seems unnecessarily confusing.

Question 24

What is the caloric nystagmus? Why is useful? What’s the mnemonic for a normal response?

Answer 24

Squirting cold or hot water in a patient’s ear should produce a nystagmus. Can be done on unconscious patients to check CN VIII activity. COWS: Cold-opposite, warm-same, referring to the fast-beat direction)

Question 25

On what lobe of the cerebellum is the ability to switch the VOR when using crazy prism-glasses that switch vision horizontally dependent?

Answer 25

The flocculonodular lobe…

Question 26

What are two inputs to the vestibular nucleus? What are two outputs from it?

Answer 26

Inputs: Vestibular system via CN VIII, flocularnodular lobe.
Outputs: Abduccens nucleus