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6a > Hearing & balance > Flashcards

Hearing & balance Flashcards

1
Q

Otic capsule

A

in the petrous portion of the temporal bone

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2
Q

Components of vestibular sensory organs

A

3 semicurcular canals, oriented 90 degrees to each other
2 otoliths
auditory cochlea
endolymphatic sac

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3
Q

Semicircular canal function

A

detect angular acceleration due to head rotations

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4
Q

Utricle/saccule

A

2 sac-like organs between semicircular canals and cochlea
utricle in the horizontal plane
saccule in the saggital plane
sense body orientation relative to gravity and linear motion

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5
Q

Perilymph

A

fills space between bony and membranous labyrinths
composition similar to extracellular/cerebrospinal fluid (low potassium and high Na)
ultrafiltrate of CSF/blood
drains via venules and middle ear mucosa

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6
Q

Endolymph

A

inside
in contiguous open lumen of semicircular canals, utricles and saccules
unique extracellular fluid - similar to intracellular fluid (high K, low Na)
produced by dark cells of sensory epithelium
absorbed by endolymphatic sac

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7
Q

Sensory epithelia components

A

Cristae of semicircular canals (3)
Maculae of utricle and saccule (2)
Sensory epithelia contain hair cells which are receptor cells and detect movement of endolymph

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8
Q

Vestibular hair cell types

A

Stereocilia - 60-100/hair cell
Kinocilium - 1/hair cell
Release glutamate as neurotransmitter

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9
Q

Vestibular hair cell distribution

A

utricles/saccules: ~35000 hair cells

Ampulla of semicircular canals: ~8000

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10
Q

Vestibular hair cell function

A

Transforms endolymph motion into neuronal signal

Bends one way: excitation; the other way: inhibition

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11
Q

Semicircular canal sensory epithelia

A

Ampulla: swelling at the end
Cristae: hair cell sensory epithelium within ampula
Cupula: acellular, gelatinous mass hinged gate spanning ampulla lumen
All hair cells in ampulla re oriented in the same direction with kinocilium closest the utricle

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12
Q

Semicicular canal arrangement

A

Pairs of crista arranged as mirror opposites

e.g. Right anterior - Left posterior

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13
Q

Otoconia

A

calcium carbonate crystals sit on top of otolithic membrane

pressure of otoconia deflects hair cell cilium

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14
Q

Utricle plane

A

horizontal

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15
Q

Saccule plane

A

vertical

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16
Q

Vestibular afferent

A

bipolar neurons

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17
Q

Vestibular ganglion

A

Scarpa’s ganglion

18
Q

CN VIII course

A

follows internal auditory meatus with facial nerve
enters brainstem at jxn of pons and medulla = cerebellopontine angle
projects to the vestibular nuclear complex, cerebellum

19
Q

Vestibular nucleus complex location

A

dorsal pons and medulla beneath 4th ventricle

20
Q

Vestibular nuclei (4)

A

Lateral
Medial
Superior
Inferior

21
Q

Lateral vestibular nucleus fxn

A

Deiter’s nucleus

innervates gravity-opposing muscles of limbs to maintain posture

22
Q

Medial vestibular nucleus fxn

A

reflex adjustments of neck and trunk muscles to restore head position after disturbance
Keep head upright

23
Q

Superior/medial vestibular nucleus fxn

A

eye movements

vestibulo-ocular reflex

24
Q

Inferior vestibular nucleus

A

integrates multi-sensory input, and cerebellum to regulate VOR gain in response to constant input

25
Q

Lateral vestibulospinal tract

A

input: utricle,saccule, semicircular canals
target: ventral horn alpha/gamma motor neurons that innervate gravity-opposing muscles of limbs

26
Q

Medial vestibulospinal tract

A

input: primarily semicircular canals
pathway: bilateral; descending MLF
Target: cervical and upper thoracic spinal cord, motor neurons innervating neck musculature

27
Q

VOR tract

A

input: semicircular canals
pathway: 3 neuron arcs
1) bipolar neurons
2) medial and superior vestibular nuclei
3) motor neurons in abducens nucleus and oculomotor nuclei that innervate oculomotor muscles

28
Q

Horizontal VOR

A

coordinates 4 muscles:
L, R lateral recti
L, R medial recti

29
Q

Vestibular nystagmus

A

rhythmic alteration of slow and fast movements during VOR
VOR: slow
Saccade: fast

30
Q

Caloric testing

A

Eye will deviate towards the cold water

and nystagmus towards the other side

31
Q

Benign paroxysmal positional vertigo

A

displaced otoconia lodged in semicircular canals

acute violent sensation of dizziness;vomiting

32
Q

Meniere’s disease

A

endolymphatic hydrops
increased endolymph in inner ear
can damage hair cells

33
Q

Vestibular neuritis

A

Viral infection of vestibulocochlear nerve

rather common; unilateral damage

34
Q

Perilymph fistula

A

breach in oval and/or round window
leaky endolymph –> decrease internal concentration
opposote of Meniere’s

35
Q

Ototoxicity

A

toxicity induced death of hair cells by some antibiotics

e.g. aminoglycosides: gentamicin, streptomycin, kanamycin, neomycin, etc

36
Q

Mal de Debarquement

A

failure of CNS plasticity to respond to prolonged movement

getting off boats/ships - people never regain land sensation (land sickness)

37
Q

Aging/dizziness/balance

A

visual/motor deficits
BPPV
gradual hair cell loss

38
Q

Bilateral vestibular dysfunction

A

occurs with ototoxicity
slow onset of loss of vestibular fxn
instability of eyes with head movements
instability when walking in the dark (no visual input)

39
Q

Unilateral vestibular dysfunction

A 
severe acute symptoms
extreme dizziness, nausea, vomiting
deviation towards side of lesion when walking
abnormal nystagmus
displaced otoconia, viral infection
40
Q

Vestibular compensation

A

Gradual recovery from unilateral lesions
learning-induced changes to central circuits
vestibular inputs ignored in favour of vision/proprioception

6a (26 decks)

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