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BMB Test 2 > B7.039 Vestibular System > Flashcards

B7.039 Vestibular System Flashcards

1
Q

bony labyrinth

A

space within the temporal bone of the skull base which contains the vestibular apparatus

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2
Q

membranous labyrinth

A

area filled with endolymph and surrounded by perilymph that lies within the bony labyrinth
gives input to auditory (cochlea) and vestibular (remainder of membranous labyrinth) systems

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3
Q

two types of vestibular receptors

A
  1. semicircular canals (kinetic labyrinth)

2. otolith organs (static labyrinth)

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4
Q

stimulus of semicircular canals

A
  1. dynamic stimuli (rotational forces)

2. head acceleration of deceleration

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5
Q

stimulus of otolith organs

A
  1. static stimuli; maintained head position (tilt)

2. translational forces; horizontal displacement

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6
Q

what are the otolith organs

A

saccule

utricle

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7
Q

functional pairs of semicircular canals

A

2 canals, one on each side of the head, that have their planes parallel
give dynamic information about rotation of the head by acting together
1. horizontal on R and L
2. anterior on R, posterior on L
3. posterior on R, anterior on L

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8
Q

structure of a semicircular canal

A
  1. attached to the utricle
  2. filled with endolymph (which is continuous from the utricle through the canal)
  3. ampulla on one end is an enlargement where vestibular hair cell receptors are located
  4. cilia of hair cells insert into a gelatinous mass called cupulla
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9
Q

ultimate function of hair cells

A

synapse with terminals of afferent axons from CN VIII

glutamate transmission

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10
Q

structure of vestibular hair cells

A

cauldron like shape with hair cells on top and synaptic vesicles at the base
1 long cilium - kinocilium
multiple smaller cilia - sterocilia

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11
Q

tonic discharge of hair cells

A

50-100 Hz

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12
Q

response to motion which bends cilia toward kinocilium

A

depolarization

increased firing rate of CN VIII afferent

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13
Q

response to motion which bends cilia away from kinocilium

A

hyperpolarization

decreased firing rate of CN VIII

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14
Q

adequate stimulus for semicircular canal receptors

A

head rotation > inertial movement of endolymph > bends cupulla and cilia of hair cell

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15
Q

effect of clockwise rotation on endolymph flow

A

counterclockwise endolymph flow

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16
Q

effect of cessation of clockwise rotation on endolymph flow

A

reversal of flow (clockwise)

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17
Q

effect of rightward rotation on horizontal canals of vestibular system

A

due to inertia, endolymph will move in opposite direction of rotation

  • in the R canal: endolymph will bend the cilia toward the kinocilium > excitation
  • in the L canal: endolymph will bend cilia away from the kinocilium > inhibition
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18
Q

barany chair test

A

clinical test of brainstem and vestibular function
subject rotated in a chair
chair is stopped and vestibular function is examined via VOR and vestibulo-postural reflexes
effects of deceleration (post-rotational component) are examined

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19
Q

3 phases in barany chair test

A
  1. acceleration to the R (rotational phase)
    - increase in R CN VIII activity
    - decrease in L CN VIII activity
  2. rotation at constant angular velocity
    - no effect after 30 s, endolymph has equilibrated
  3. deceleration (post rotational phase)
    - decrease in R CN VIII activity
    - increase in L CN VIII activity
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20
Q

effect of rotation on vestibulospinal neurons

A

rotation to the R > increased R CN VIII firing > extensors on the R are activated
i.e. rotation to a side increases activation of extensors on that side and decreases activation of extensors on the opposing side

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21
Q

which direction will a patient fall after a barany chair test?

A

in direction of rotation
in post-rotational phase, activation switches due to shifting of equilibrium during rotation
SO if youre spinning R, youre activating your R side extensors, BUT when you stop, you start activating your L side extensors
thus, when you get up post-spinning, your L side extensors are activated and your R side are not, so you fall R

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22
Q

what is the vestibulo-ocular reflex (VOR)

A

when a subject is rotated to the right, the eyes move to the left
for this to happen, the activity of the L lateral rectus and R medial rectus must increase while the opposite muscles activity will decrease

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23
Q

nystagmus

A

slow movements opposing rotation, followed by fast reset movements
ie when turning R, slow movement to the L with a fast reset to the R

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24
Q

pathways of the VOR

A

increased CN VIII firing > increased medial vestibular nucleus firing > decreased abducens nucleus firing rate > decreased contraction of LR
AND
decreased 3rd nerve nucleus firing rate on opposite side > decreased contraction of medial rectus

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25
Q

internuclear ophthalmoplegia

A

lesions to the medial longitudinal fasciculus prevent eye from rotating medially in response to lateral rotation of opposite eye (fibers which connect abducens to oculomotor travel in MLF)
results in nystagmus

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26
Q

phases of nystagmus

A
  1. direction of nystagmus is names by direction of the fast phase
  2. slow phase is the VOR
  3. fast phase is non vestibular
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27
Q

what is a caloric test

A

irrigation of the canal with warm/cold water to induce physiologic nystagmus
water creates a convection current in the endolymph

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28
Q

warm water caloric test

A

produces nystagmus to the same side (fast movement toward same side)

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29
Q

cold water caloric test

A

produces nystagmus to the opposite side (fast movement toward opposite side)

30
Q

vertigo

A

illusory feeling of spinning, falling, or giddiness with disorientation in space that usually results in a disturbance of equilibrium

31
Q

what happens to balance when vestibular damage occurs

A

still good if you have vision

visual info can compensate for loss of both labyrinths

32
Q

characterize unilateral lesions of the vestibular nerve

A
  1. CN VIII afferents have a high background firing rate
  2. anything that produces an imbalance of input from semicircular canals on each side will elicit vestibulo-ocular and vestibulo-postural reflexes
  3. a lesion on one side sets up an imbalance in favor of the opposite side
  4. subject tends to fall toward the side of the lesion and has nystagmus to opposite side
33
Q

lesions to the L CN VIII

A

produces same effect as rotation to the R

imbalance in L and R CN VIII input can be more disabling than no input at all

34
Q

motor functions performed by the cerebellum

A
  1. oculomotor control
    - adaptive control of eye movements
    - eye stability control (VOR)
    - eye blink conditioning
  2. switching reflexes on and off
  3. modifying the strength of reflexes
  4. motor learning
35
Q

overall function of cerebellum

A

add the fine tuning to make voluntary movements and a variety of different reflexes correct in terms of strength and timing

36
Q

layers of the cerebellum

A

midline - vermis

2 lateral lobes - cerebellar hemispheres

37
Q

contents of cerebellum

A

cerebellar cortex and underlying cerebellar white matter

white matter contains 4 paired deep cerebellar nuclei

38
Q

cerebellar nuclei

A 
from medial to lateral:
fastigial
globose
emboliform
dentate
39
Q

vestibulo-cerebellum

A

small structure on the caudal end of cerebellum

has vestibular connections and is concerned with equilibrium and eye movements

40
Q

vermis projections

A

brain stem area concerned with control of axial and proximal limb muscles

41
Q

cerebellar hemisphere projections

A

control of distal limb muscles

42
Q

cerebrocerebellum

A

lateral portions of hemispheres

interact w motor cortex in planning and programming movements

43
Q

spinocerebellum

A

vermis + medial hemisphere portions
receives proprioceptive info from the body
motor execution, correction of movement errorspurkinje fiber

44
Q

cerebellar peduncles

A

attach cerebellum to the brainstem and contain pathways to and from the brainstem

45
Q

inferior cerebellar peduncle

A

contains fiber systems from spinal cord and lower brainstem (olivocerebellar fibers from inferior olivary nucleus)
vestibular inputs

46
Q

middle cerebellar peduncle

A

fibers from contralateral pontine nuclei

47
Q

superior cerebellar peduncle

A

efferent fibers that send impulses to thalamus and spinal cord, with relays in the red nuclei

48
Q

purkinje cells

A

provide primary output from the cerebellar cortex
have cell bodies in purkinje cell layer and have dendrites that fan out in a single plane
axons project ipsilaterally to deep cerebellar nuclei, where they form inhibitory synapses (GABA)

49
Q

granule cells

A

cell bodies in granular layer of cerebellar cortex
only excitatory neurons in cerebellar cortex
send axons upward into molecular layer where they bifurcate and become parallel fibers
run perpendicular through purkinje dendrites and form excitatory synapses on the dendrites (glutamate)

50
Q

inputs to cerebellum

A
  1. climbing fibers

2. mossy fibers

51
Q

climbing fibers

A

origin from interior olivary nucleus
powerful, obligatory synapses on a small number of (1-10) of purkinje cells
collaterals to deep cerebellar nuclei

52
Q

mossy fibers

A

from pontine nuclei and spinocerebellar tracts
make excitatory synapses with granule cells
parallel fibers of granule cells make synapses with a large number (10,000) of purkinje cells, thus most fiber influence is widely distributes

53
Q

cells in the deep cerebellar nuclei

A

project to the thalamus which then goes to the motor cortex

other projections go to descending pathways

54
Q

pukinje cell response to inputs

A

climbing fibers lead to all or non response
climbing fibers elicit a complex spiking pattern
mossy fiber contribution is simple and graded

55
Q

feedforward model of motor control

A

motor cortex > motor output > cutaneous/proprioceptive afferents > sensory cortex
in between these steps, there is input related to expected output vs actual output
between these two measurements, error correction is made and fed back through the system

56
Q

how does info about actual movement travel to the cerebellum

A

spinocerebellar tract (mossy)

57
Q

how does info about intended movement travel to the cerebellum

A

via pontine inputs (mossy)

58
Q

how does error connection signal travel from cerebellum

A

out through deep cerebellar nuclei to both thalamus > motor cortex and red nucleus > spinal cord

59
Q

neocerebellar functional circuit (initiation and programming of movement)

A

limbic system > frontal cortex > pontine nuclei > cerebrocerebellum (lateral hemisphere) > dentate nucleus > ventral lateral nucleus of thalamus > motor cortex > muscles > movement

60
Q

somatotopic organization of the cerebellum

A

spinal input is somatotopically organized
organization maintained throughout interconnections with other brain structures
vermis = trunk
cerebellar hemispheres = ipsilateral motor coordination and muscle tone

61
Q

cerebellar regulation of vestibulo-postural reflexes

A

adds fine tuning to ensure correct amplitude, strength, and range of movement

62
Q

function of VOR

A

allows eyes to fixate on a stationary visual target in the presence of head movement
eye movements are equal and opposite to head movements

63
Q

suppression of the VOR by vestibulo-cerebellum

A

inhibitory activity of purkinje fibers opposes typical excitatory activity from CN VIII afferents from head movement
two inputs cancel each other out allows for eyes to move with head and leaving the firing rate of vestibular nucleus cells unchanged

64
Q

other examples of motor adaptation that depend on the cerebellum

A
  1. wearing reverse prisms
  2. compensation for unilateral destruction of the vestibular labyrinth or cutting the vestibular nerve
  3. adaptations in limb movements similar to the reversing prism experiment with eye movements
  4. adapting to unexpected changes in external load
65
Q

lesions of the vestibulocerebellum

A

nystagmus and disequilibrium or wavering, ataxic gait

  • example is medulloblastoma in children
  • also can be damaged in chronic alcoholism
66
Q

cerebellar syndrome

A

lesions of the cerebrocerebellum and spinocerebellum

67
Q

hypotonia

A

loss of input to gamma system

68
Q

ataxia/ asynergia

A

lack of coordinated movements
associated with errors in metrics of movement (velocity, force, direction) and difficulty terminating movements at the desired point (dysmetria)

69
Q

intention tremor or action tremor

A

tremor associated with voluntary movement

irregular frequency but around 10-12 cycles per second

70
Q

adiadochokinesis

A

inability to make rapid, alternating movements (rapid pronation/supination of the hands)

71
Q

decomposition of movement

A

complex movements involving multiple joints are not made with continuous smooth trajectories

BMB Test 2 (22 decks)

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