auditory function and balance Flashcards
vestibular system: identify the functions and list the types of signals derived from the vestibular system
input into brain from a) eye b) (inner) ear c) foot
a) visual b) rotation, movement and gravity c) pressure
outputs from brain based on inuputs
ocular reflex, postural control, nausea
type 1 hair cell in transduction: number, afferent and efferent, shape
more in number, direct afferent, indirect efferent, round (similar to inner in hearing)
type 2 hair cell in transduction: number, afferent and efferent, shape
fewer in number, direct afferents and efferents, long and thin (similar to outer in hearing)
location of hair cells in Otolith organs (utricle and saccule), and displacement plane and liquid location
utricule (hair cells inferior - linear displacement, liquid on top), saccule (hair cells unilateral - vertical displacement, liquid elsewhere)
static labyrinth: structures in otolith organs, and what are otoliths
maculae (have hair cells), hair cells, gelatinous matrix (on top of hair), otoliths (carbonate crystals)
static labyrinth: where is striola and impact upon hair bundle movement
central part of maculae, where on left and right there are opposing hair bundle polarities as orientated in separate dirctions (symmetrical), so any movement in any direction stimulates a distinct subset of cells (excitation one side and inhibition other side); movement causes Ca2+ influx and release of neurotransmitter to nerve
kinetic labyrinth: semicircular canals
hair cells only in ampulla (crista); less dense gelatinous matrix (cupula) vs otolith organs; kinocilia (same direction on each side of head, so no striola section and symmetry; instead entire cell is in opposite direction, gaining symmetry this way and allowing excitation and inhibition); anterior canal (45 degrees front), posterior canal (45 degrees back), lateral canal (30 degrees)
blood supply of vestibular system
some shared with brain as well as ear: anterior inferior cerebellar artery from basilar artery branches to inner ear and cerebellum, so stroke with inner ear symptoms but actually in anterior inferior cerebellar artery (brain stroke)
6 normal functions of vestibular system
subserve perception of movement in space and tilt with respect to gravity.
provide reflex balance reactions to sudden instability of gait or posture ‘vestibulo-spinal reflexes’; stabilise eyes on earth fixed targets preserving visual acuity during head movements ‘vestibular-ocular reflexes’; assist control of blood pressure and heart rate during rapid up-down tilts; assist synchronisation of respiration with body reorientations; provokes motion sickness when stimulated in unusual motion environments; provide reference of absolute motion in space, helping interpret relativistic signals of other senses in creating a perception of spatial orientation
what does hair cell synapse with
primary neurone dendrite (cell body in Scarpas ganglion)
what does primary neurone project to
vestibular nuclei in brainstem
what stimulates hair cell
deflection by forces of intertial resistance to acceleration (gravity for otoliths) and endolymphatic fluid rotation (canals)
hair cell receptor potential: which directions cause depolarisation and hyperpolarisation
depolarisation caused by deflection towards kinocilium; hyperpolarisation caused by deflection away from kinocilium
ganglion cell discharge: which directions increase and decrease firing frequency
increased firing frequency towards kinocilium; decreased firing frequency away from kinocilium
2 locations where primary afferents of vestibular nerves end
in vestibular nuclei and in cerebellum
4 vestibular nuclei
superior, lateral, medial, inferior
organisation of static labyrinth
otoliths in lateral and inferior vestibular nuclei
organisation of kinetic labyrinth
superior and medial vestibular nuclei
diagram of vestibular nuclei in dorsal view
slide 18
4 locations where vestibular nuclei project
spinal cord, nuclei of extraocular muscles, cerebellum, ANS centres for cardiovascular and respiratory control
diagram of vestibular pathways
slide 19
where do vestibular nuclei receive input from
hair cells in semicircular canals or otolith organs via vestibular nerve
superior and lateral vestibular nuclei pathway
medial lemniscus to ventroposterior nuclei -> internal capsule to vestibular cortex (superior temporal gyrus, posterior to primary motor cortex)
lateral, medial and inferior vestibular nuclei: 3 pathways for reflex
vestibulospinal reflex, vestibulo-ocular reflex, vestibulocerebellar reflex
vestibulospinal reflex: via what and to where
lateral vestibulospinal tract to limb and trunk; medial vestibulospinal tract to upper back and neck
vestibulo-ocular reflex: via what and to where
medial longitudinal fasciculus to oculomotor nucleus (oculomotor nerve -> superior, medial and inferior rectus), abducens nucleus (abducens nerve -> lateral rectus), trochlear nucleus (trochlear nerve -> superior oblique)
vestibulocerebellar reflex: via what and to where
inferior cerebellar peduncle to vestibulo-cerebellum (flocculonodular lobe)
3 functions of vestibulocerebellar pathways
movement coordination, posture regulation, VOR modulation
what region of the diencephalon do some vestibular nuclei project to
thalamus
where do thalamic nuclei project to
head region of primary somatosensory cortex and superior parietal cortex
what is vestibular cortex (superior parietal cortex) concerned with
spatial orientation
what might cortical projections account for
dizziness (vertigo) during certain kinds of vestibular testing
2 regions of vestibular cortex where thalamic nuclei project to
PIVC (parieto-insular vestibular cortex) and PIC (posterior insular cortex)
2 sections of cerebellum
vermis, flocconodular lobe (most inferior)
2 functions of vestibulocerebellum
maintenance of balance, control eye movements
2 functions of spinocerebellum
regulation of muscle tone, coordination of skilled voluntary movement
function of cerebrocerebellum
planning of voluntary activity
3 sensory inputs of cerebellum
visual, vestibular, proprioceptive
2 central processing of input in cerebellum
primary processor (vestibular nuclear complex), adaptive processor (cerebellum)
2 motor outputs of primary processor (vestibular nuclear complex)
motor neurones for eye movements or positional movements
3 functions of vestibular system
detect and inform about head movements, keep images fixed in retina during head movements, postural control
why does each canal have a resting discharge (tonic firing rate)
always have stimuli inside ear (e.g. gravity), so still have some discharge from hair cells to nerve (increases during excitation, decreases during inhibition); when head is still, tonuses from right and left canals balance out
otolith organs: what causes movement of hair bundles
linear acceleration (utricle), tilt and vertical acceleration (saccule); stimulated by inertial resistance of otoconial mass to linear head acceleration (tends to stay still when head moves); omni-directional
otolith organs: effect of movement
depolarisation (excitation) or hyperpolarisation (inhibition) of nerves, with vector sum of utricular and saccular stimulation patterns providing signal of linear acceleration in all 3D directions
otolith organs: movement of utricule
horizontal (hair cells project vertically with directional sensitivities in all combinations of lateral and anteroposterior directions)
otolith organs: movement of saccule
vertical (hair cells with their overlaying layer of otoconia project normal to the plane with directional sensitivities in all combinations of vertical and anteroposterior directions)
semi-circular canals: response to angular acceleration
endolymph flow in opposite direction to head motion, pushing against cupula
response to acceleration vs velocity
inertia at constant velocity so no cupula movement
semi-circular canal pairing
one side stimulated and other inhibited by same movement as in same plane: both horizontal (lateral), left anterior paired with right posterior, right anterior paired with left posterior
how are semi-circular canals unidirectionally orientated
hair cells project from ampulla in wall of canal and are unidirectionally oriented, so that acceleration phase of head rotation to a particular side or direction preferentially stimulates canals on that side e.g. rotation to right stimulates right canal, and rotation in opposite direction inhibits canal activity
what happens to semi-circular canals when head rotation decelerates to stop (ie acceleration in the opposite direction)
canal on opposite side is stimulated e.g. stopping rightwards rotation stimulates left canal
2 vestibular reflexes
vestibulo-spinal reflex, vestibuo-ocular reflex
2 vestibulo-spinal reflex pathways
lateral vestibulo-spinal tract, medial vestibulo-spinal tract
lateral vestibulo-spinal tract: side and innervation to
ipsilateral, motor neurones to limb muscles
medial vestibulo-spinal tract: side and innervation to
bilateral, motor neurones to neck and back muscles
diagram of 2 vestibulo-spinal reflex pathways
slide 39
lateral vestibulo-spinal tract pathway
12:00 slide 40
lateral vestibulo-spinal tract pathway
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medial vestibulo-spinal tract pathway
slide 41
medial vestibulo-spinal tract pathway
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function of vestibuo-ocular reflex
keep images fixed while head is moving
vestibuo-ocular reflex: what 2 nuclei does it connect
vestibular nuclei and oculomotor nuclei
vestibuo-ocular reflex: latency
5-7ms (very fast) so don’t realise it is happening (reflex)
vestibuo-ocular reflex: eye and head movement relation
eye movement in opposite direction to head movement
structure of eye
slide 43
vestibulo-ocular pathways
slide 44
vestibulo-ocular pathways
info from oculomotor (III) and abducens (VI) for medial and lateral; excitation and inhibition
vestibulo-ocular pathways
slide 45
horizontal vestibulo-ocular pathway
slide 46
horizontal vestibulo-ocular pathway
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vertical vestibulo-ocular pathway (anterior)
slide 47
vertical vestibulo-ocular pathway (anterior)
one side stimulates one side and inhibits other
vertical vestibulo-ocular pathway (posterior)
slide 48
vertical vestibulo-ocular pathway (posterior)
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effect of loss of canal function on one side
gives a permanent partial impairment of sensitivity to rotation in the’ on’ direction of the defunct canal
effect of loss of otolith function on one side
no effect as omni-directional (all directions)
