Lecture 13 Flashcards
Resting discharge rate of hair cells
100 hz
discharge when hair cells pulled towards kinocilium and utricle (horizontal canals)
excitation, discharge rate increases
discharge when hair cells pulled away from kinocilium and utricle (horizontal canals)
inhibition, firing rate decreases
Describe orietation if hair cells
hair cells in the ampulla are all orientated in the same direction and act as a population
result of angular acceration of the head
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
function of semi-circular canals
detects angular accelerations
Describe results of movement of the head to the left
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
Describe location of structures of semi-circular canals
utricle along the midline, ampulla in anterior part adjacent to utricle
Otilith organs
utricle and saccule
function of otilith organs
sense linear accelerations and effects of gravity
Describe anatomy of otilith organs
-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
Describe location and orientation of otilith organs
On floor of utricle and wall of saccule have otilith organs. In utricle- hair cells project vertically. In saccule-hair cells project vertically
Orietation of hair cells of utricle and result of linear acceleration
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.
Orietation of hair cells of saccule and result of linear acceleration
-hair cells pointing away from striola, hair cells excited when pulled away from striola
Describe anatomy of vestibular sensory neurons
-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
Identify 4 vestibular nuclei
-lateral vetibular nucleus (LVN)
-Medial vestibular nucleus (MVN)
-Superior vestibular nucleus (SVN)
-Inferior vestibular nucleus (IVL)
Result of damage to vestibulo-cochlear nerve
loss of balance and hearing
4 vestibular nuclei gives rise to…
vestibulospinal tracts, including 2 descending motor tracts
Gives rise to lateral vestibulospinal tracts (LVST)
Lateral vestibular nucleus (LVN)
Function of lateral vestibulospinal tracts
controls balance and extensor tone in limbs
Gives rise to medial vestibulospinal tract (MVSP)
medial vestibular nucleus (MVN) and inferior vestibular nucleus (IVN)
Function of medial vestibulospinal tracts
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.
Medial vestibulospinal tract and lateral vestibulospinal tract travel _____
bilaterally
Identify vestibular nuclei outputs and to cranial nuclei and functions
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)
Describe other vestibular nuclei outputs and functions
-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.
Describe primary vestibular cortex
-majority agrees there is area that receives vestibular info along parietal cortex deep within sylvian fissue called the operculum
Function of vestibulo-ocular reflex and relavance
Allow individual to keep eyes fixed on target while moving head. Helps to identify injury.
Describe movement of eyes, fluid and head movement with vestibuloocular reflex
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.
What does continues vestibular stimulation lead to
“Nystagmus” (beating eyes)
Describe the different phased of nystagmus and patten of movement with head rotation
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
Describe general pathway of vestibular info (VOR)
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.
Identify ways of measuring nystagmus
-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
Identify tests for normal nystagmus (see if vetibularocular reflexes intact)
- 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
Describe the caloric irrigation test
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.
