Vestibular system

Question 1

What is meant with bottom up and top down activation?

Answer 1

• Bottom up for reflex with retinal input: regulation from the caudate/putamen –> GPi –> VA/VL complex thalamus –> frontal cortex
• Top down for goal directed with other inputs: regulation from the caudate/putamen –> SNr –> superior colliculus

Question 2

What types of eye movement do we have?

Answer 2

Shifting gaze: saccades, smooth pursuit movements,vergence movements
Stabilizing gaze: vestibulo-ocular movements, optokinetic movements

Question 3

What are saccades?

Answer 3

Rapid ballistic movement of the eye
(during REM)

Question 4

What are smooth pursuit movements?

Answer 4

Small tracking movements, is voluntary

Question 5

What is vergence movement?

Answer 5

What you see when you align the fovea of each eye with targets located at different distances

Question 6

Why does our gaze have to be stabalized?

Answer 6

To compensate for head movements –> vestibulo-ocular of vestibular cues, optokinetic of visual cues

Question 7

What does the vestibular system do?

Answer 7

Processes sensory information underlying motor responses to and perceptions of:
self motion, head position, spatial organization relative to gravity, helping stabalize gaze, head and posture

Question 8

What is the peripheral and central portion of the vestibular system?

Answer 8

Peripheral: inner ear structures
- Linear accelorometers, angular velocity sensors
Central: vestibular nuclei
- Integrative center, input from visual system, output to gaze centers and postural muscles: balance

Question 9

What are the 2 otolith organs of the vestibular system and for what do they function?

Answer 9

Utricle and saccule, which translate movements

Question 10

Why does the vestibular system have 3 semicircular canals?

Answer 10

For detection of rotations of the head

Question 11

In the utricle and saccule are 2 populations of hair cells directed in opposing direction, what structure divides these within the organs?

Answer 11

Striola

Question 12

What are the hair cells in the utricle and saccule called?

Answer 12

Macula

Question 13

In which direction do the stereocilium point in opposition of the striola?

Answer 13

• Utricle: haircells go TO striola
• Saccule: haircells point away from the striola

Question 14

With what kind of head movements do the utricle and saccule correspond with?

Answer 14

Utricle: Head tilts from side to side (horizontal)
Saccule: Head tilts forward and backward (vertical)

Question 15

What is the membrane called in which the hair cells project to?

Answer 15

Otolithic membrane with otoconia (ear stones, from calcium carbonate crystals)

Question 16

How do otoconia and hair cells work together?

Answer 16

Otoconia weight pulls on otholitic membrane due to gravitational force. Hair cells react to this. Half population will depolarize and other have will hyperpolarize

Question 17

What is crista and cupula in the vestibular system?

Answer 17

Both within the semicircular canals
Crista is sensory epithelium
Cupula is a gelatinous mass with the stereocilia of the hair cells inside + its a barrier for the endolyth

NOTE
no axis of symmetry, only one axis for depolarization

Question 18

What is the function of the capula?

Answer 18

Translates head movement into neural signals through interaction with haircells.

Rotation: head rotates –> endolymph fluid inside semicircular canals lags behind due to enertia –> motion causes capula to bend in opposite direction of head –> deflection of stereocilia –> direction of deflection causes hyper or depolarization

Question 19

Head rotations in the right horizontal plane causes …..

Answer 19

Depolarization

Question 20

Head rotations in the left horizontal plane causes ……..

Answer 20

Hyperpolarization

Question 21

What happens when there is inflammation of the vestibular system

Answer 21

Hair cells degenerate –> no tonic activity on left, normal tonic activity on right side