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PHYL 2041 > Vestibular System > Flashcards

Vestibular System Flashcards

1
Q

What is the vestibular system?

A

Sensory system that provides a sense of balance and spatial orientation to coordinate movements

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2
Q

What does vestibular system detect?

A

Linear (vertical or horizontal) or angular acceleration of head

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3
Q

What is acceleration?

A

Change in velocity over time

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4
Q

What causes acceleration?

A

Force acts on mass

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5
Q

What does vestibular labyrinth form?

A

Works with cochlea to form inner ear

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6
Q

What makes up vestibular labyrinth?

A
  • 3 semicircular canals (angular)
  • 2 otolith organs→utricle (horizontal), saccule (vertical)
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7
Q

What makes up membranous labyrinth?

A
  • 3 semicircular canals (angular)
  • 2 otolith organs→utricle (horizontal), saccule (vertical)
  • Cochlear duct
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8
Q

What contains endolymph?

A

Membranous labyrinth

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9
Q

Endolymph of vestibular apparatus is…

A

In direct contact with endolymph in scala media of cochlea, and is generated by stria vascularis lining scala media

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10
Q

Membranous labyrinth enclosed in…

A

Bony labyrinth

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11
Q

What is the bony labyrinth?

A

Series of bony cavities in petrous part of temporal bone that protects the membranous labyrinth

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12
Q

What is vestibular labyrinth innervated by?

A

Vestibular nerve

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13
Q

What makes up vestibulocochlear/8thcranial nerve?

A

Vestibulocochlear nerve and cochlear nerve

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14
Q

Where are cell bodies making up vestibular portion of vestibulocochlear nerve!

A

Scapas ganglion

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15
Q

What kind of neurons are vestibular ones?

A

Bipolar

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16
Q

How do vestibular neutrons make synapses?

A

Each neuron has a peripheral process toward vestibular labyrinth to synapse with sensory receptors in semi circular canas or otolith organs

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17
Q

Where do vestibular neurons relay info to

A

Vestibular nuclea in brainstem via central processes in neuron

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18
Q

How many semicircular canals and planes?

A

3 canals lie in 3 planes forming right angles with eachother (orthogonal plane)

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19
Q

Each canal in right ear has…

A

Corresponding canals in other ear

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20
Q

What do semicircular canals detect?

A

Angular heel acceleration

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21
Q

What is the ampulla?

A

Swelling at end of semi circular canal

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22
Q

Hair cells in ampulla

A
  • Crista (hair sensory receptor cells
  • On basal side they firm synaptic connections with Afferent of vestibular neurons, forming vestibular part of 8th cranial nerve
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23
Q

Stereocilia in ampulla

A

Hair cells in ampulla have one tall cilia (stereocilia) that protrude into cupula and are in direct contact with endolymph

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24
Q

What is cupula?

A

Gelatinous area surrounded by and soaked in endolymph

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25
Q

Steps of angular acceleration in semi circular canals

A

Head rotation in plane → fast movement of labyrinth walls and cupula (same direction) → liquidendolymph is slower, exerts pushes cupula against direction of head movements→stereocilia bend toward stereocilium →vestibular hair cells activated →ion channels open → K ions into hair cells (depolarization) →VGCCs open →glutamate release →postsynaptic membrane depolarizes and APs fire

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26
Q

Opposite directions semicircular canal angular transduction

A

Head rotation opp way causes endolymph to push cupula to other side, causing cilia to bend away from largest stereocilium. This causes closure of all mechanical ion channels, hyperpol, reducing conductance of VGCCs and reducing glu release—postsynaptic neurons hyperpol, less APs

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27
Q

Do vestibular canals respond to deceleration?

A

Yes

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28
Q

What happens to the other ear during head rotation?

A

Increase in firing rate of vestibular neurons in one ear, decrease in firing rate of vestibular neurons in the other ear

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29
Q

Macula of otolith organs

A

Both utricle and saccule have a macula that contains hair and support cells

30
Q

Stereocilia of otolith hair cells

A

Project into gelatinous otolithic membrane

31
Q

Otolithic membrane surface is…

A

Crusted with otoconia CaCO3 particles

32
Q

Otoconia density is…

A

Higher than surrounding endolymph

33
Q

Steps of linear acceleration in otolith organs

A

Linear acceleration →force on otoconia→otolithic membrane moves in direction of tilt→hair cells bend toward stereocilia, MGICs open, hair cell depol OR away from stereocilia, MGICs close, hair cell hyperpol → hair cell depol/hyperpol increases/decreases respectively Glu release onto vestibular neurons innervating hair cells →Glu acts on postsyn memb, and increase/decrease of Glu cases increase/decrease respectively of APs

34
Q

Direction selectivity of hair cell responses

A

Hair cell responses ARE direction selective, each hair cell has its own preferred movement direction

35
Q

Movement of hair cells by X amount elicits max response

A

Less than 0.5 um

36
Q

Does deflection of cilia perpendicular to preferred direction affect opening of MGICs?

A

No

37
Q

Are hair cells in otolith organ maculae oriented in same direction?

A

No

38
Q

What plane is utricle macula in?

A

Horizontal

39
Q

What plane is saccule macula in?

A

Vertical

40
Q

What mirrors what in each ear

A

Saccule macula and utricle macula

41
Q

What happens to right ear if vestibular neurons innervating left ear increase AP firing in response to linear acceleration?

A

Vestibular neurons decrease AP firing rate

42
Q

What directions can otolith organs sense linear acceleration in? Why?

A

All, due to systematic acceleration direction variation—hair cells cover all directions in plane

43
Q

How does CNS receive info to interpret linear movements?

A

From otolithic hair cells

44
Q

___ with cell body in ___ project to ___ in ____ and ___

A

Primary vestibular neurons, scarpa’s ganglion, vestibular nuclei, brainstem, cerebellum

45
Q

Do otolith and semicircular canal input converge?

A

Yes

46
Q

What other input does vestibular nuclei receive? Why is this important?

A

Visual, propriceptive, and input from cerebellum abt movement. Allows them to analyze complex head movement

47
Q

2 functions of info processed in vestibular nuclei:

A
  1. Spatial orientation and motion
  2. Controls rapid reflexes of head/eye/limb/trunk
48
Q

What functions as premotor reflex arc neurons?

A

Neurons in vestibular nuclei

49
Q

Primary projections of vestibular nuclei target ___, which relays info to ____ and ____.

A

Thalamic nuclei, cortex (motion/spatial), cerebellum (movement)

50
Q

Secondary projections of vestibular nuclei serve 2 reflexes:

A
  1. Vestibulo-ocular reflex—extraocular neurons
  2. Postural reflex—brain/spinal cord
51
Q

Function of vestibulo-ocular reflex

A

Eye movements that counter head movements

52
Q

What happens to vestibulo-ocular reflex when head is rotated in horizontal plane?

A

Hair cells in semicircular canal on side toward turning motion are depolarized, hair cells on other side are hyperpolarized

53
Q

In vestibulo-ocular reflex, what do vestibular neurons on the turning side do?

A

Increase firing, excite neurons in medial vestibular nucleus

54
Q

What gives rise to 6th cranial nerve?

A

Excitatory fibres from medial vestibular nucleus projecting to contralateral abdomens nucleus

55
Q

Where is the abducens nucleus?

A

Pons

56
Q

What does the abducens nucleus contain?

A

Motor neurons and interneurons

57
Q

2 outputs of abducens nucleus:

A
  1. Lateral rectus eye muscle on same side contracts, pulling eye away from midline
  2. Contralateral oculomotor nucleus contains motor axons that innervate medial rectus muscle on same side, pulling eye toward midline
58
Q

What do inhibitory projections from medial vestibular nucleus to ipsilateral abducens nucleus do?

A

Prevents excitation of ipsilateral rectus muscle and contralateral medius muscle

59
Q

What is the point of the vestibulo-ocular reflex?

A

Eyes move to right when head moves to left and vice versa

60
Q

What resets eyes to original position after vestibulo-ocular reflex?

A

Fast saccade

61
Q

What is physiological nystagmus?

A

Reflex that counters head rotation

62
Q

How is vestibulo-ocular reflex used clinically?

A

Tests nerve integrity and connections between nuclei using caloric testing

63
Q

How does caloric testing work?

A
  1. One ear is irrigated with cold or warm water
  2. Cold water: convection currents in canals cause nerve to cool, mimicking movement of head away from the cooled ear. Eyes will move toward irrigated ear if vestibulo-ocular reflex is working
64
Q

What causes loss of vestibulo-ocular reflex?

A

Abducens nerve or vestibular system dysfunction

65
Q

What causes asymmetric eye movements?

A

Oculimotor nerve dysfunction

66
Q

2 major pathways of connections of vestibular nuclei to motor neurons and interneurons:

A
  1. Projections from medial vestibular nucleus neurons form medial vestibulospinal tract, which projects to motor neurons in cervical spinal cord that control neck muscles (vestibulocervical reflex)
  2. Projections from (mostly lateral) vestibular nuclei form lateral vestibular tract, which projects ipsilaterally along spinal cord to synapse onto motor neurons (vestibulospinal reflex)
67
Q

Function of vestibulocervical reflex:

A

Neck movements that counteract passive head movements

68
Q

Example of vestibulocervical reflex

A

Head moving forward when falling forward

69
Q

How does vestibulocervical reflex innervate?

A

Otolith organs send signal to medial vestibular nucleus, which projects to spinal cord motor neurons that innervate neck muscles

70
Q

Function of vestibulospinal reflex:

A

Body tilts against linear acceleration

71
Q

How does vestibulospinal reflex innervate?

A

Vestibular neurons in otolith organs activate lateral vestibular nucleus neurons, which excite spinal cord motor neurons that innervate extensor muscles of limb on ipsilateral side to maintain upright posture

PHYL 2041 (2 decks)

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