Vestibular Anatomy and Function

Question 1

Functions of vestibular system

Answer 1

Postural control
- postural stability
- postural orientation

Gaze stability
- stabilize visual image during head movement

Provide sensory information for spatial orientation

Question 2

Postural stability

Answer 2

maintenance of COM within BOS

Question 3

Postural orientation

Answer 3

ability to maintain relationship between body segments and between body and environment for a task

Question 4

Sensory systems (input) for postural control

Answer 4

Visual
Vestibular
Somatosensory

Question 5

Vestibular system output

Answer 5

VOR: vestibular ocular reflex

VSR: vestibulo-spinal reflexes

VCR: vestibulo-colic reflex

Question 6

peripheral vestibular structures

Answer 6

Vestibular end organ
- 3 semicircular canals
- 2 otolith organs (utricle, saccule)

CN VIII (vestibular portion aka after it passes thru auditory meatus)

Question 7

Peripheral vestibular blood supply

Answer 7

Basilar a. –>
Anterior inferior cerebellar artery (AICA) –>
Labyrinthine a. –>
Anterio-vestibular a.
Common cochlear a.

Question 8

Vestibular end organ

Answer 8

Bony labyrinth
- in temporal bone
- houses vestibular apparatus in cochlea

Membranous labyrinth
- 3 semicircular ducts
- 2 otolith: utricle, saccule
- All five contain endolymph

Hair cells convert head motion into neural firing

Question 9

Otoliths: utricle and saccule

Answer 9

Function is linear motion detection
- tilt
- forward/backward
- up/down

Utricle is oriented in more horizontal plane
- detects lateral tilting of head

Saccule is oriented in more vertical plane
- detects forwards/backwards and up/down motion

Question 10

Otolith anatomy and physiology

Answer 10

Otolithic membrane: gelatinous macula

Otoconia: provide shear forces for hair cell deflection
- change in position causes gelatinous membrane to shift, causing sheer force

Tonic discharge

Push/pull relationship

Think plate of jello

Question 11

Semicircular canals

Answer 11

Anterior (superior)
- excitation = anterior rotation of head aka flexion/extension

Posterior (inferior)
- excitation = posterior rotation of head aka lateral flexion

Horizontal (lateral)
- excitation = rotation towards same side

Function
- detect angular motion
- provide afferent input to central vestibular nuclei about head position

Question 12

Semicircular canals mechanism

Answer 12

Ampulla houses cupula which houses many hair cells

Endolymph flow (opposite of head motion) deflects cupula –> results in depolarization –> sends signal to brain that head is moving

Excite one side, inhibit the other

Question 13

peripheral and central meet

Answer 13

Vestibular portion of CN VIII is a bipolar neuron w/ cell bodies in Scarpa’s ganglion

CN VII and VIII
- travel together thru internal auditory meatus
- enter pontomedullary junction of brain at cerebellopontine angle

Question 14

Vestibular ocular reflex (VOR)

Answer 14

Stabilize gaze during head movement
- 1:1 head:eye movement in equal, opposite directions

3-neuron reflex arc
- scarpa’s (vestibular) ganglion –> vestibular nuclei –> oculomotor nuclei in BS (CN III, IV, VI)
- produces compensatory eye mvmt in plane of stimulated canal
- inhibits antagonistic mm.

Question 15

cont. @ central vestibular system

Answer 15

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