Hearing & balance

Question 1

Otic capsule

Answer 1

in the petrous portion of the temporal bone

Question 2

Components of vestibular sensory organs

Answer 2

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

Question 3

Semicircular canal function

Answer 3

detect angular acceleration due to head rotations

Question 4

Utricle/saccule

Answer 4

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

Question 5

Perilymph

Answer 5

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

Question 6

Endolymph

Answer 6

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

Question 7

Sensory epithelia components

Answer 7

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

Question 8

Vestibular hair cell types

Answer 8

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

Question 9

Vestibular hair cell distribution

Answer 9

utricles/saccules: ~35000 hair cells

Ampulla of semicircular canals: ~8000

Question 10

Vestibular hair cell function

Answer 10

Transforms endolymph motion into neuronal signal

Bends one way: excitation; the other way: inhibition

Question 11

Semicircular canal sensory epithelia

Answer 11

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

Question 12

Semicicular canal arrangement

Answer 12

Pairs of crista arranged as mirror opposites

e.g. Right anterior - Left posterior

Question 13

Otoconia

Answer 13

calcium carbonate crystals sit on top of otolithic membrane

pressure of otoconia deflects hair cell cilium

Question 14

Utricle plane

Answer 14

horizontal

Question 15

Saccule plane

Answer 15

vertical

Question 16

Vestibular afferent

Answer 16

bipolar neurons

Question 17

Vestibular ganglion

Answer 17

Scarpa’s ganglion

Question 18

CN VIII course

Answer 18

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

Question 19

Vestibular nucleus complex location

Answer 19

dorsal pons and medulla beneath 4th ventricle

Question 20

Vestibular nuclei (4)

Answer 20

Lateral
Medial
Superior
Inferior

Question 21

Lateral vestibular nucleus fxn

Answer 21

Deiter’s nucleus

innervates gravity-opposing muscles of limbs to maintain posture

Question 22

Medial vestibular nucleus fxn

Answer 22

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

Question 23

Superior/medial vestibular nucleus fxn

Answer 23

eye movements

vestibulo-ocular reflex

Question 24

Inferior vestibular nucleus

Answer 24

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

Question 25

Lateral vestibulospinal tract

Answer 25

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

Question 26

Medial vestibulospinal tract

Answer 26

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

Question 27

VOR tract

Answer 27

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

Question 28

Horizontal VOR

Answer 28

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

Question 29

Vestibular nystagmus

Answer 29

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

Question 30

Caloric testing

Answer 30

Eye will deviate towards the cold water | and nystagmus towards the other side

Question 31

Benign paroxysmal positional vertigo

Answer 31

displaced otoconia lodged in semicircular canals | acute violent sensation of dizziness;vomiting

Question 32

Meniere's disease

Answer 32

endolymphatic hydrops increased endolymph in inner ear can damage hair cells

Question 33

Vestibular neuritis

Answer 33

Viral infection of vestibulocochlear nerve | rather common; unilateral damage

Question 34

Perilymph fistula

Answer 34

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

Question 35

Ototoxicity

Answer 35

toxicity induced death of hair cells by some antibiotics | e.g. aminoglycosides: gentamicin, streptomycin, kanamycin, neomycin, etc

Question 36

Mal de Debarquement

Answer 36

failure of CNS plasticity to respond to prolonged movement | getting off boats/ships - people never regain land sensation (land sickness)

Question 37

Aging/dizziness/balance

Answer 37

visual/motor deficits BPPV gradual hair cell loss

Question 38

Bilateral vestibular dysfunction

Answer 38

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)

Question 39

Unilateral vestibular dysfunction

Answer 39

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

Question 40

Vestibular compensation

Answer 40

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