Vestibular System

Question 1

function of the vestibular system

Answer 1

maintain balance relative to gravity at rest and during movement

Question 2

vestibule-ocular reflex

Answer 2

stabilizes images on the retina during head movement by moving the eyes in the direction opposite of the head movement (nystagmus)

does NOT require visual input

Question 3

vestibulo-spinal reflex

Answer 3

coordinates head and neck movement with the trunk and body along vestibulospinal tracts

Question 4

lateral/medial vestibulospinal tracts

Answer 4

descending axonal projections from vestibular nuclei to spinal cord to maintain posture

Question 5

what part of the ear is the vestibular component

Answer 5

inner ear

Question 6

function of the inner ear

Answer 6

maintains balance and equilibrium by measuring linear and angular acceleration of the head

made of bony and membranous labyrinths

Question 7

bony labyrinth

Answer 7

hollowed out petrous temporal bone filled with perilymph

Question 8

membranous labyrinth

Answer 8

membrane lining of the bony labyrinth filled with endolymph

Question 9

function of semicircular ducts

Answer 9

detect angular acceleration of the head/body using crust ampullaris

Question 10

crista ampullaris

Answer 10

hair cell receptors (3 total - one in each semicircular duct) that have hair cells lined up in a single plane

Question 11

detection of angular acceleration

Answer 11

rotational movement causes the endolymph to slowly move and displace the cupula –> bends hair cells

Question 12

function of utricle/saccule

Answer 12

otolithic organs that detect linear acceleration of the head/body

Question 13

macula

Answer 13

hair cell receptors (2 total - one in utricle, one in saccule) that have multiple stereo cilia and 1 kinocilium that project onto an overlying gelatinous membrane

Question 14

detection of linear acceleration

Answer 14

linear movement causes hair cells to move –> otolithic membrane lags and bends the hair cells –> causes depolarization/hyperpolarization

Question 15

what does stereocilia bending TOWARD kinocilium cause

Answer 15

depolarization –> generates action potential

Question 16

what does stereocilia bending AWAY from kinocilium cause

Answer 16

hyperpolarization –> no AP generated

Question 17

how many total receptors are there in each ear

Answer 17

five (2 macula, 3 crista ampulla)

Question 18

vestibular neural pathway

Answer 18

1. primary afferent (bipolar) has cell body located in vestibular ganglion of CN VIII
2. primary afferent axons project ipsilaterally to vestibular nuclei to synapse with secondary afferents
3. secondary afferent projects ipsilaterally and contralaterally from vestibular nuclei to medial geniculate nuclei
   (also side branches to other CNs)
4. secondary afferents synapse with tertiary afferents in the medial geniculate nuclei
5. tertiary afferents project to the cerebral cortex

Question 19

efferent vestibular pathways

Answer 19

1. lateral vestibulospinal tract
2. medial vestibulospinal tract
3. cerebellum
4. reticular formation

Question 20

lateral vestibulospinal tract

Answer 20

descending axons from the neurons in the IPSILATERAL vestibular nuclei through the ventral funiculus

projects to ventral spinal cord interneurons to:
1. activate alpha/gamma motor neurons to ipsilateral extensors
2. inhibit all flexors
3. inhibit alpha/gamma motor neurons to contralateral extensors

Question 21

signs of lateral vestibulospinal tract dysfunction

Answer 21

flexion on ipsilateral side, extension on contralateral side

Question 22

medial vestibulospinal tract

Answer 22

ascending axons from the neurons in the ipsilateral vestibular nuclei through the ventral funiculus of the cervical and cranial-thoracic spinal cord
- innervates the neck muscles

Question 23

connection of vestibular system to cerebellum

Answer 23

pathways via the ipsilateral caudal cerebellar peduncle; extend between vestibular nuclei and flocculonodular lobe

Question 24

connection of vestibular system to reticular formation

Answer 24

responsible for maintenance of consciousness

Question 25

clinical signs of vestibular dysfunction

Answer 25

signs are IPSILATERAL
1. loss of equilibrium
2. nystagmus
3. head tilt
4. tight circling
5. strabismus
6. ataxia
7. nausea/vomiting/salivation

Question 26

pendular nystagmus

Answer 26

equal side to side with no fast/slow phase
(looks like a tremor)

Question 27

jerk nystagmus

Answer 27

slow phase with a fast recovery phase to the opposite side

named by direction of fast phase

Question 28

characterizing jerk nystagmus

Answer 28

• horizontal, vertical, rotational
• positional, non-positional
• conjugate, disconjugate

Question 29

what side will strabismus go

Answer 29

ventral/ventro-lateral

ipsilateral to dysfunction

Question 30

peripheral dysfunction

Answer 30

nystagmus: horizontal or rotary, non-positional, conjugate

associated with facial nerve paralysis, Horner’s syndrome, otitis external, tympanic bulla/TMJ/pharyngeal pain

Question 31

bilateral peripheral disease

Answer 31

no nystagmus (physiologic or pathologic), crawling/crouching, symmetric ataxia, wide side to side movements

Question 32

signs of central dysfunction

Answer 32

disease of the vestibular nuclei or cerebellum and pathways

nystagmus: vertical, positional, and disconjugate

altered level of consciousness
other cranial nerve deficits
long tract signs (postural reaction deficits, paresis/paralysis)
cerebellar signs