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Neurology (Spring 2015) > L03: Vestibulocochlear Function & Vestibular Syndromes (Carrera) > Flashcards

L03: Vestibulocochlear Function & Vestibular Syndromes (Carrera) Flashcards

1
Q

Vestibular function***

A
  • maintenance of posture/balance (head and body)
  • functions intimately w/ the cerebellum
  • can be peripheral or central
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2
Q

CN 8 name and chars.

A

vestibulocochlear n.

  • ONLY cn to exit skull
  • ONLY sensory
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3
Q

2 portions of cn8

A

1) vestibular

2) auditory

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4
Q

only cn to exit skull

A

8 (vestibulocochlear)

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5
Q

vestibulocochlear neurons synapse where?

A

with specialized “hair” cells in receptor organs of the inner ear that transform mechanical deformation into neural signals

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6
Q

sensory receptors for hearing are located where

A

cochlea in the Organ of Corti

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7
Q

transduction of hearing takes place in the:

A

Organ of Corti (houses hair cells)

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8
Q

blood supply to cochlea

A

stria vascularis

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9
Q

3 main components of cochlea

A

scala vestibuli
scala tympani
scala media/cochlear duct

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10
Q

middle ear houses:

A

ossicles (amplifiers of sound waves). First ossicle attaches to tympanic membrane

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11
Q

sound waves come into bulla and hit tympanic membrane which then conducts to rest of inner ear

A

:)

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12
Q

cochlear projections

A
  • leave the spiral ganglion and enter brainstem at medulla oblongata/pons
  • synapse in the cochlear nucleus
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13
Q

basic auditory pathway

A

inner ear –> cochlear nuclei in medulla –> pons –> midbrain –> auditory complex of forebrain

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14
Q

precocial species

A 
(born with fully formed brains and functional hearing)
chicken
sheep
cattle 
horses
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15
Q

altricial species

A

(born without fully formed brains and functional hearing)
humans
monkeys
dogs, cats

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16
Q

conductive deafness

A

failure of conduction of sound waves from the ear canal to the inner ear due to occlusion of the ear canal
-congenital or acquired (ie. rupture of tympanic membrane, exudate, ossicles with age, etc.)

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17
Q

sensorineal deafness

A

alterations of the neural structures of the auditory pathway

-congenital (hair cells of OoC) or acquired (infection, intracranial dz)

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18
Q

which animals susceptible to congenital sensorineural deafness

A

American Paint horses
lethal white foals
dalmatians
white dogs and cats with blue eyes

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19
Q

vestibular labyrinth

A
  • composed of utricle and saccule
  • located in large vestibule
  • detects static or kinetic position (gravity and linear acceleration)**
20
Q

macula

A

covered by hair cells projecting into gelatinous otolithlic membrane that contains otoliths

21
Q

semicircular ducts

A

detect angular movements of the head

  • located in semicircular canal
  • receptor: crista ampullaris
22
Q

where is entry into the skull?

A

internal acoustic meatus

23
Q

where is entry into the brain?

A

@ lvl of trapezoid body and caudal cerebellar peduncle

-axons synapse onto cn8 or enter cerebellum

24
Q

components of vestibular system

A 
cerebellum
brainstem
cn8
vertical and horizontal ear canals
semicircular canals
tympanic bulla
25
Q

vestibular nuclei

A

4 on each side of brainstem

brainstem dz will almost always reslt in vestibular dz b/c these nuclei take up so much space on brainstem

26
Q

axonal projections from vestibular nuclei

A
  • vestibulospinal tracts from spinal cord for anti-gravity muscles
  • Medial Longitudinal Fasciculus rostrally for ocular and head movements
27
Q

lateral vestibular nucleus projects to contra or ipsilateral ventral funiculus?**

A

IPSILATERAL; mediates anti-gravity system on ipsilateral side

28
Q

medial longitudinal fasciculus rostral projections

A
  • nuclei of cn3,4,6

- responsible for oculocephalic reflex

29
Q

medial longitudinal fasciculus caudal projections

A
  • medial vestibulospinal tract

- maintains body and limb position relative to the head

30
Q

extraocular muscles innervation

A

cn3 (oculomotor): dorsal, medial, ventral recti mm.
cn4 (trochlear): dorsal oblique m. (OPPOSITE SIDE)
cn6 (abducent): lateral rectus and retractor bulbi mm.

31
Q

physiologic nystagmus

A

moves eyes to hold images during head rotation or target motion

32
Q

MLF connects cn8 to which cn?

A

3,4,6

33
Q

vomiting center

A
  • in reticular formation of the medulla

- receives afferent input from the vestibular portion of the vestibulocochlear n.

34
Q

cerebral projections

A
  • synapse in thalamus

- provide conscious awareness of the body’s position in space

35
Q

“if you excite on one side, you get ipsilateral facilitation of extensors and contralateral facilitation of flexors”

A

:)

36
Q

when you are vestibular, you lean/tilt towards or away from lesion?

A

TOWARDS. If a lesion prevents activation of one side, the ipsilateral nuclei won’t be excited as much as the other side, so you get relative facilitation of extensors on the normal side and lack of facilitation on the affected side.

37
Q

CS of vestibular lesion

A

head tilt
circling, leaning, falling TOWARDS lesion
unilateral or asymmetric ataxia TOWARDS lesion
abn. eye position or movements
nausea
+/- postural reaction deficits

38
Q

nystagmus

A

involuntary movements of the eyes

-defined by direction of the fast phase

39
Q

pathologic nystagmus moves which directions?

A

horizontal, rotary, or vertical

40
Q

pendular nystagmus

A
  • not actually nystagmus
  • due to a defect in visual pathways
  • common in Himalayans, Siamese
41
Q

Central vs. Peripheral vestibular

A

central: involves brainstem or cerebellum
peripheral: involves ear canal, bulla, cn8

42
Q

CS of CENTRAL vestibular lesion

A 
proprioceptive deficits
dullness, stupor
head tilt
other cn deficits
strabismus
nystagmus (especially VERTICAL)
cerebellar and forebrain signs
43
Q

CS of PERIPHERAL vestibular lesion

A 
NO proprioceptive deficits
normal mentation
head tilt toward lesion
only cn7 or 8 deficits
strabismus
nystagmus (any direction)
*Can manifest as Horner's syndrome!*
44
Q

If something affects bulla, will commonly affect which nerve?

A

cn7 (facial n.)

45
Q

Paradoxical vestibular syndrome

A

head tilt AWAY from the lesion, while fast phase of nystagmus may be TOWARD the lesion

  • ALWAYS CENTRAL (not peripheral)
  • lesion is on same side as proprioceptive deficits

Neurology (Spring 2015) (7 decks)

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