Lecture 13

Question 1

Resting discharge rate of hair cells

Answer 1

100 hz

Question 2

discharge when hair cells pulled towards kinocilium and utricle (horizontal canals)

Answer 2

excitation, discharge rate increases

Question 3

discharge when hair cells pulled away from kinocilium and utricle (horizontal canals)

Answer 3

inhibition, firing rate decreases

Question 4

Describe orietation if hair cells

Answer 4

hair cells in the ampulla are all orientated in the same direction and act as a population

Question 5

result of angular acceration of the head

Answer 5

Angular acceleration of the head causes endolymph fluid to lag behind due to inertia and deflect the cupula and ciliia

-With the head at rest steady flow of impulses is produced
-As head turns, the liquid in the semicircular canals lags behind, bending the cupula and its hair cells. the output of nerve impulses changes
-when head moves in opposite direction, the hair cells are bent in a different way. Output changes once again

Question 6

function of semi-circular canals

Answer 6

detects angular accelerations

Question 7

Describe results of movement of the head to the left

Answer 7

Inertia leads fluid to move to the right (opposite), in left canal this deflects cupulla towards utricle increasing the firing rate. In right canal fluid pulls cupula away from utricle decreasing the firing rate

Question 8

Describe location of structures of semi-circular canals

Answer 8

utricle along the midline, ampulla in anterior part adjacent to utricle

Question 9

Otilith organs

Answer 9

utricle and saccule

Question 10

function of otilith organs

Answer 10

sense linear accelerations and effects of gravity

Question 11

Describe anatomy of otilith organs

Answer 11

-Hair cells in maccula have cilia embedded in otilithic membrane
-Calcium crystals (otoconia/otiliths) fixed atop the membrane
-Hair cell receptors have axons projecting to cell bodies in vestibular ganglion

Question 12

Describe location and orientation of otilith organs

Answer 12

On floor of utricle and wall of saccule have otilith organs. In utricle- hair cells project vertically. In saccule-hair cells project vertically

Question 13

Orietation of hair cells of utricle and result of linear acceleration

Answer 13

Hair cells within utricle oriented towards striola (imaginary line). Hair cells on one side excited if directed towards striola, hair cells on opposite side also orietated that dircted towards striola they are excited. Hair cells excited when pointing topards striola. If have linear acceration, horizontally translate, hair cells pulled towards striola on one half will be excited and those on other half pulled away are inhibited.

Question 14

Orietation of hair cells of saccule and result of linear acceleration

Answer 14

-hair cells pointing away from striola, hair cells excited when pulled away from striola

Question 15

Describe anatomy of vestibular sensory neurons

Answer 15

-vestibular afferents have cell bodies in vestibular ganglion; axons travel via vestibulo-cochlear nerve (CN VIII) to ipsilateral side of brainstem where synapse on vestibular nuclei

Question 16

Identify 4 vestibular nuclei

Answer 16

-lateral vetibular nucleus (LVN)
-Medial vestibular nucleus (MVN)
-Superior vestibular nucleus (SVN)
-Inferior vestibular nucleus (IVL)

Question 17

Result of damage to vestibulo-cochlear nerve

Answer 17

loss of balance and hearing

Question 18

4 vestibular nuclei gives rise to…

Answer 18

vestibulospinal tracts, including 2 descending motor tracts

Question 19

Gives rise to lateral vestibulospinal tracts (LVST)

Answer 19

Lateral vestibular nucleus (LVN)

Question 20

Function of lateral vestibulospinal tracts

Answer 20

controls balance and extensor tone in limbs

Question 21

Gives rise to medial vestibulospinal tract (MVSP)

Answer 21

medial vestibular nucleus (MVN) and inferior vestibular nucleus (IVN)

Question 22

Function of medial vestibulospinal tracts

Answer 22

Controls tone and reflexes of muscles: positioning of the head and neck (vestibulo-collic reflexes). Interaction of vestibular system and neck muscles- reflex to keep head in space while body is moving. Relys on proprioceptoive info from neck and integration with vestibular signals.

Question 23

Medial vestibulospinal tract and lateral vestibulospinal tract travel _____

Answer 23

bilaterally

Question 24

Identify vestibular nuclei outputs and to cranial nuclei and functions

Answer 24

Superior vestibular nucleus (SVN) and medial vestibular nucleus (MVN) project via medial longitudinal fasciculus (MLF) to 3 cranial nuclei:
-oculo-motor nucleus (in midbrain)
-trochlear nucleus (in midbrain)
-abducens nucleus (in pons)
Functions for controlling eye muscles/reflexes (i.e. Vestibular oculular reflexes)

Question 25

Describe other vestibular nuclei outputs and functions

Answer 25

-cortex via the thalamus: pathways from superior vestibular nucleus, cell bodies have axons that porject upwards bilaterally to thalamus, and then from thalamus nuecli have axons that project gto cortex. Functions in conscious perception of head orientation/movement -Reciprical projections with cerebellum: vestibular outputs ipsilaterally to cerebellum. Cerebellum also has inputs back to vestibular nuclei. Functions in balance, eye control, movement coordination.

Question 26

Describe primary vestibular cortex

Answer 26

-majority agrees there is area that receives vestibular info along parietal cortex deep within sylvian fissue called the operculum

Question 27

Function of vestibulo-ocular reflex and relavance

Answer 27

Allow individual to keep eyes fixed on target while moving head. Helps to identify injury.

Question 28

Describe movement of eyes, fluid and head movement with vestibuloocular reflex

Answer 28

Eyes go opposite to head movement in same direction as cupula. Eyes move same direction as fluid, opposite to head movement. E.g. if head moves to the left, fluid to right, eyes to the right.

Question 29

What does continues vestibular stimulation lead to

Answer 29

"Nystagmus" (beating eyes)

Question 30

Describe the different phased of nystagmus and patten of movement with head rotation

Answer 30

Slow phase- VOR Fast phase, corrective response. Head to left, eyes move right to a point (slow phase VOR), fast phase snaps eyes back to laft (counteractive reflex). Nystagmus left beating, named after fast phase

Question 31

Describe general pathway of vestibular info (VOR)

Answer 31

Movement of head activities receptors (hair cell)- one side excited other side inhibited, axon travel ipsilateral to brainstem project to vestibular nuclei, controlling eye muscles. Side that is excited has the greatest influence on movement.

Question 32

Identify ways of measuring nystagmus

Answer 32

-frenzel glasses: allows for clinicians to look at eyes magnifying glasses, for subjects makes vision blurry so cant fixate on object - electronystagmography: electrical measure of eye movement, involves placing electrodes around eyes, polarity of eye change with rotation, differential of signal - video-nystagmography/video oculography (VNG or VOG): high speed video cameras measuring eye velocities, goggles with infrared light into eye- view of pupil software that detects eye movements

Question 33

Identify tests for normal nystagmus (see if vetibularocular reflexes intact)

Answer 33

- rotating chair test- tests horizontal canals, slower velocity of rotating chair movement, not high accelerations, use either VNG or VOG to record eye movement, record nastagmus - Head impulse test (HIT): tests canals in all planes, much faster accelerations - Caloric irrigation tes: irrigate ear with cold/warm water, use EMG to see movement

Question 34

Describe the caloric irrigation test

Answer 34

Cool water causes endolympth in ear to cool and sink. Convection current with pull cupula in clockwise direction. Hot water will cause oppositely directed nystagmus COWS (cold opposite, warm same) e.g. warm in right ear, right nystagmus, VOR left. Cold water in right ear, left beating nystagmus, VOR to right.