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NEUROSCIENCE > 27 + 28 – Vestibular System > Flashcards

27 + 28 – Vestibular System Flashcards

1
Q

What are the components of the vestibular system?

A
  1. Vestibular apparatus
  2. CN 8
  3. Vestibular nuclei (medulla)
  4. Vestibulocerebellum (flocculonodular lobe)
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2
Q

Vestibular apparatus consists of:

A

-membranous labyrinth (inner ear)
-sensory structure (hair cells)
* paired structure (L+R)

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3
Q

Vestibular apparatus detects:

A

-static position
-linear + rotational motion of the head

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4
Q

Vestibular apparatus location:

A

-inside the petrous part of the temporal bone

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5
Q

What is the embryonic origin of the vestibular apparatus?

A

-otic vesicles
>vestibular apparatus
>cochlea

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6
Q

What are the parts of the vestibular apparatus, membranous labyrinth (3)?

A

-semi-circular canals
-utricle
-saccule

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7
Q

Perilymph vs. endolymph:

A

-endolymph is what is in the inside the canals and is surrounded by…
-perilymph=CSF

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8
Q

Hair cells:

A

-sensory structures inside the vestibular apparatus (and cochlea)
-not the same length
*convert peripheral sensations to nerve impulses
>transmitted via CN 8!

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9
Q

If fall hair cells fall to where they are taller vs. shorter:

A

-taller: excitatory signal
-shorter: inhibitor signal

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10
Q

Membranous labyrinth:

A

-system of soft tissues AND receptors

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11
Q

Cristae ampullares (x3):

A

-located at base of each semicircular duct
*detect rotational changes

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12
Q

Cupula:

A

-protein-rich structure that is neutrally-buoyant
-what the cristae ampullares ‘float’ in

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13
Q

What are the structures in the walls of the utricle and saccule?

A

-maculae (x2)
>floating in cupula
>one horizontal, one vertical
*detect static and linear movement
*PAIRED structures

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14
Q

Otoliths:

A

-tiny stones on surface of capsule of macula
-detect gravitational force that is being pushed on the ‘fluid bubble’ and then onto the hair cells
*pressure on here that is being detected

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15
Q

Cranial nerve 8:

A

-vestibulocochlear nerve
-inputs info INTO the medulla
-pathway if very SHORT
>vestibular apparatus is near brainstem

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16
Q

CN 8 sensory axons enter:

A

-medulla and synapse MOSTLY on vestibular nuclei within the medulla
*ganglia is OUTSIDE the CNS

17
Q

CN 8 most peripheral input occurs in:

A

-vestibular nuclei (medulla)
-some axons synapse directly within cerebellum
>vestibulocerebellum (flocculonodular lobe)

18
Q

Information from the vestibular nuclei goes to:

A

-LMN of neck/limbs/trunk
-LMN of extrinsic ocular muscles (CN 2, 4, 6)
-cortex (via thalamus): conscious awareness of head movement
-medulla to the emetic center: nausea/motion sickness

19
Q

Vestibular nuclei are:

A

-UMN
>vestibulospinal tract

20
Q

Vestibular nuclei UMN input to LMN of head/limbs/trunk:

A

-activate ipsilateral extensors
-inhibitory to ipsilateral flexors
-inhibitory to contralateral extensors

21
Q

Vestibular nuclei UMN input to ocular muscles:

A

-CN 3, 4, 6 (MEDIAL LONGITUDINAL FASCICULUS: coordinates eye movements)
*ocular muscles need to work in synchrony
>L+R eye movements are coordinated by OPPOSITE muscle activation/inhibition

22
Q

If the animal wants to move to the left what happens with the ocular muscles?

A

-L eye: activate lateral muscles, inhibit medial muscles
-R eye: activate medial muscles, inhibit lateral muscles

23
Q

Physiological nystagmus examples:

A

-rapid, involuntary movement of eyes (horizontal, rotational, vertical)
-slow-phase away from direction of head movement
-saccade

24
Q

Rapid, involuntary movement of eyes (nystagmus):

A

-coordinated movements between L+R eyes
-eyes don’t move smoothly with re-positioning of head
>step-wise movements

25
Q

Saccade:

A

-fast-phase coordinated movement of eyes moving TOWARDS the direction of head movement
>delay in eye movement compared to head movement

26
Q

Vestibular disease:

A

-can effect ANYWHERE within the vestibular system
>vestibular apparatus
>vestibular nuclei
>CN 8
>flocculonodular region of cerebellum

27
Q

What will lesions of vestibular disease result in overall?

A

-REDUCED activity of the vestibular system on the IPSILATERAL side

28
Q

What are the lesions of vestibular disease?

A
  1. Asymmetrical head/body position
  2. Ataxia: vestibular ataxia
  3. Pathological nystagmus (spontaneous)
  4. Positional strabismus
29
Q

Asymmetrical head/body position (vestibular disease):

A

*TOWARDS the side of the lesion
-head tilt
-body leaning/falling
-rolling

30
Q

Vestibular ataxia (vestibular disease):

A

-‘circling’ (not fully circling as that is a forebrain lesion)
*falling TOWARDS the side of the lesion (staggering)

31
Q

Pathological nystagmus (spontaneous) (vestibular disease):

A

*can help determine if it is a peripheral or central lesion
-imbalance between L+R vestibular systems, AND reduced input to medial longitudinal fasciculus
*FAST-phase AWAY from lesion (towards the more active side of the body)
-horizontal, vertical, or rotational

32
Q

Positional strabismus (vestibular disease):

A

-abnormal eye position when head is moved/rotated
-ipsilateral VENTRAL or VENTROLATERAL strabismus when they are moved dorsally

33
Q

Lots of compensation with vestibular disease:

A

-most clinical signs will resolve over time
>nystagmus and strabismus resolve most rapidly (days to weeks)

34
Q

If you suspect vestibular disease, but you don’t see nystagmus. What can you do?

A

-re-position and spontaneous nystagmus may return

35
Q

Peripheral vestibular disease:

A

-head tilt towards side of lesion
-nystagmus (horizontal or rotary, no change with head position)
-normal postural reactions
-concurrent facial nerve damage or Horner’s syndrome (ipsilateral)

36
Q

Central vestibular disease:

A

-head tilt towards vs. away (paradoxical)
-nystagmus (horizontal, rotary, or vertical, direction may change with head position)
-+/- postural deficits (ipsilateral)
-multiple CN deficits (ipsilateral or bilateral, can see Horner’s signs)

37
Q

Paradoxical vestibular disease:

A

-when lesions effect the cerebellum (particularly the peduncles or the vestibular regions)
>vestibular nuclei are NOT INHIBITED (that side is more active, so go to the less active side)
-head tilt away from lesion
-gait and postural deficits: hypermetria, postural deficits IPSILATERAL to lesion

NEUROSCIENCE (25 decks)

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