auditory function and balance

Question 1

input into brain from a) eye b) (inner) ear c) foot

Answer 1

a) visual b) rotation, movement and gravity c) pressure

Question 2

outputs from brain based on inuputs

Answer 2

ocular reflex, postural control, nausea

Question 3

type 1 hair cell in transduction: number, afferent and efferent, shape

Answer 3

more in number, direct afferent, indirect efferent, round (similar to inner in hearing)

Question 4

type 2 hair cell in transduction: number, afferent and efferent, shape

Answer 4

fewer in number, direct afferents and efferents, long and thin (similar to outer in hearing)

Question 5

location of hair cells in Otolith organs (utricle and saccule), and displacement plane and liquid location

Answer 5

utricule (hair cells inferior - linear displacement, liquid on top), saccule (hair cells unilateral - vertical displacement, liquid elsewhere)

Question 6

static labyrinth: structures in otolith organs, and what are otoliths

Answer 6

maculae (have hair cells), hair cells, gelatinous matrix (on top of hair), otoliths (carbonate crystals)

Question 7

static labyrinth: where is striola and impact upon hair bundle movement

Answer 7

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

Question 8

kinetic labyrinth: semicircular canals

Answer 8

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)

Question 9

blood supply of vestibular system

Answer 9

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)

Question 10

6 normal functions of vestibular system

Answer 10

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

Question 11

what does hair cell synapse with

Answer 11

primary neurone dendrite (cell body in Scarpas ganglion)

Question 12

what does primary neurone project to

Answer 12

vestibular nuclei in brainstem

Question 13

what stimulates hair cell

Answer 13

deflection by forces of intertial resistance to acceleration (gravity for otoliths) and endolymphatic fluid rotation (canals)

Question 14

hair cell receptor potential: which directions cause depolarisation and hyperpolarisation

Answer 14

depolarisation caused by deflection towards kinocilium; hyperpolarisation caused by deflection away from kinocilium

Question 15

ganglion cell discharge: which directions increase and decrease firing frequency

Answer 15

increased firing frequency towards kinocilium; decreased firing frequency away from kinocilium

Question 16

2 locations where primary afferents of vestibular nerves end

Answer 16

in vestibular nuclei and in cerebellum

Question 17

4 vestibular nuclei

Answer 17

superior, lateral, medial, inferior

Question 18

organisation of static labyrinth

Answer 18

otoliths in lateral and inferior vestibular nuclei

Question 19

organisation of kinetic labyrinth

Answer 19

superior and medial vestibular nuclei

Question 20

diagram of vestibular nuclei in dorsal view

Answer 20

slide 18

Question 21

4 locations where vestibular nuclei project

Answer 21

spinal cord, nuclei of extraocular muscles, cerebellum, ANS centres for cardiovascular and respiratory control

Question 22

diagram of vestibular pathways

Answer 22

slide 19

Question 23

where do vestibular nuclei receive input from

Answer 23

hair cells in semicircular canals or otolith organs via vestibular nerve

Question 24

superior and lateral vestibular nuclei pathway

Answer 24

medial lemniscus to ventroposterior nuclei -> internal capsule to vestibular cortex (superior temporal gyrus, posterior to primary motor cortex)

Question 25

lateral, medial and inferior vestibular nuclei: 3 pathways for reflex

Answer 25

vestibulospinal reflex, vestibulo-ocular reflex, vestibulocerebellar reflex

Question 26

vestibulospinal reflex: via what and to where

Answer 26

lateral vestibulospinal tract to limb and trunk; medial vestibulospinal tract to upper back and neck

Question 27

vestibulo-ocular reflex: via what and to where

Answer 27

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)

Question 28

vestibulocerebellar reflex: via what and to where

Answer 28

inferior cerebellar peduncle to vestibulo-cerebellum (flocculonodular lobe)

Question 29

3 functions of vestibulocerebellar pathways

Answer 29

movement coordination, posture regulation, VOR modulation

Question 30

what region of the diencephalon do some vestibular nuclei project to

Answer 30

thalamus

Question 31

where do thalamic nuclei project to

Answer 31

head region of primary somatosensory cortex and superior parietal cortex

Question 32

what is vestibular cortex (superior parietal cortex) concerned with

Answer 32

spatial orientation

Question 33

what might cortical projections account for

Answer 33

dizziness (vertigo) during certain kinds of vestibular testing

Question 34

2 regions of vestibular cortex where thalamic nuclei project to

Answer 34

PIVC (parieto-insular vestibular cortex) and PIC (posterior insular cortex)

Question 35

2 sections of cerebellum

Answer 35

vermis, flocconodular lobe (most inferior)

Question 36

2 functions of vestibulocerebellum

Answer 36

maintenance of balance, control eye movements

Question 37

2 functions of spinocerebellum

Answer 37

regulation of muscle tone, coordination of skilled voluntary movement

Question 38

function of cerebrocerebellum

Answer 38

planning of voluntary activity

Question 39

3 sensory inputs of cerebellum

Answer 39

visual, vestibular, proprioceptive

Question 40

2 central processing of input in cerebellum

Answer 40

primary processor (vestibular nuclear complex), adaptive processor (cerebellum)

Question 41

2 motor outputs of primary processor (vestibular nuclear complex)

Answer 41

motor neurones for eye movements or positional movements

Question 42

3 functions of vestibular system

Answer 42

detect and inform about head movements, keep images fixed in retina during head movements, postural control

Question 43

why does each canal have a resting discharge (tonic firing rate)

Answer 43

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

Question 44

otolith organs: what causes movement of hair bundles

Answer 44

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

Question 45

otolith organs: effect of movement

Answer 45

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

Question 46

otolith organs: movement of utricule

Answer 46

horizontal (hair cells project vertically with directional sensitivities in all combinations of lateral and anteroposterior directions)

Question 47

otolith organs: movement of saccule

Answer 47

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)

Question 48

semi-circular canals: response to angular acceleration

Answer 48

endolymph flow in opposite direction to head motion, pushing against cupula

Question 49

response to acceleration vs velocity

Answer 49

inertia at constant velocity so no cupula movement

Question 50

semi-circular canal pairing

Answer 50

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

Question 51

how are semi-circular canals unidirectionally orientated

Answer 51

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

Question 52

what happens to semi-circular canals when head rotation decelerates to stop (ie acceleration in the opposite direction)

Answer 52

canal on opposite side is stimulated e.g. stopping rightwards rotation stimulates left canal

Question 53

2 vestibular reflexes

Answer 53

vestibulo-spinal reflex, vestibuo-ocular reflex

Question 54

2 vestibulo-spinal reflex pathways

Answer 54

lateral vestibulo-spinal tract, medial vestibulo-spinal tract

Question 55

lateral vestibulo-spinal tract: side and innervation to

Answer 55

ipsilateral, motor neurones to limb muscles

Question 56

medial vestibulo-spinal tract: side and innervation to

Answer 56

bilateral, motor neurones to neck and back muscles

Question 57

diagram of 2 vestibulo-spinal reflex pathways

Answer 57

slide 39

Question 58

lateral vestibulo-spinal tract pathway

Answer 58

12:00 slide 40

Question 59

lateral vestibulo-spinal tract pathway

Answer 59

MORE

Question 60

medial vestibulo-spinal tract pathway

Answer 60

slide 41

Question 61

medial vestibulo-spinal tract pathway

Answer 61

MORE

Question 62

function of vestibuo-ocular reflex

Answer 62

keep images fixed while head is moving

Question 63

vestibuo-ocular reflex: what 2 nuclei does it connect

Answer 63

vestibular nuclei and oculomotor nuclei

Question 64

vestibuo-ocular reflex: latency

Answer 64

5-7ms (very fast) so don't realise it is happening (reflex)

Question 65

vestibuo-ocular reflex: eye and head movement relation

Answer 65

eye movement in opposite direction to head movement

Question 66

structure of eye

Answer 66

slide 43

Question 67

vestibulo-ocular pathways

Answer 67

slide 44

Question 68

vestibulo-ocular pathways

Answer 68

info from oculomotor (III) and abducens (VI) for medial and lateral; excitation and inhibition

Question 69

vestibulo-ocular pathways

Answer 69

slide 45

Question 70

horizontal vestibulo-ocular pathway

Answer 70

slide 46

Question 71

horizontal vestibulo-ocular pathway

Answer 71

MORE

Question 72

vertical vestibulo-ocular pathway (anterior)

Answer 72

slide 47

Question 73

vertical vestibulo-ocular pathway (anterior)

Answer 73

one side stimulates one side and inhibits other

Question 74

vertical vestibulo-ocular pathway (posterior)

Answer 74

slide 48

Question 75

vertical vestibulo-ocular pathway (posterior)

Answer 75

MORE

Question 76

effect of loss of canal function on one side

Answer 76

gives a permanent partial impairment of sensitivity to rotation in the’ on’ direction of the defunct canal

Question 77

effect of loss of otolith function on one side

Answer 77

no effect as omni-directional (all directions)