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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
Steps of angular acceleration in semi circular canals
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
26
Opposite directions semicircular canal angular transduction
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
27
Do vestibular canals respond to deceleration?
Yes
28
What happens to the other ear during head rotation?
Increase in firing rate of vestibular neurons in one ear, decrease in firing rate of vestibular neurons in the other ear
29
Macula of otolith organs
Both utricle and saccule have a macula that contains hair and support cells
30
Stereocilia of otolith hair cells
Project into gelatinous otolithic membrane
31
Otolithic membrane surface is…
Crusted with otoconia CaCO3 particles
32
Otoconia density is…
Higher than surrounding endolymph
33
Steps of linear acceleration in otolith organs
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
Direction selectivity of hair cell responses
Hair cell responses ARE direction selective, each hair cell has its own preferred movement direction
35
Movement of hair cells by X amount elicits max response
Less than 0.5 um
36
Does deflection of cilia perpendicular to preferred direction affect opening of MGICs?
No
37
Are hair cells in otolith organ maculae oriented in same direction?
No
38
What plane is utricle macula in?
Horizontal
39
What plane is saccule macula in?
Vertical
40
What mirrors what in each ear
Saccule macula and utricle macula
41
What happens to right ear if vestibular neurons innervating left ear increase AP firing in response to linear acceleration?
Vestibular neurons decrease AP firing rate
42
What directions can otolith organs sense linear acceleration in? Why?
All, due to systematic acceleration direction variation—hair cells cover all directions in plane
43
How does CNS receive info to interpret linear movements?
From otolithic hair cells
44
___ with cell body in ___ project to ___ in ____ and ___
Primary vestibular neurons, scarpa's ganglion, vestibular nuclei, brainstem, cerebellum
45
Do otolith and semicircular canal input converge?
Yes
46
What other input does vestibular nuclei receive? Why is this important?
Visual, propriceptive, and input from cerebellum abt movement. Allows them to analyze complex head movement
47
2 functions of info processed in vestibular nuclei:
1. Spatial orientation and motion 2. Controls rapid reflexes of head/eye/limb/trunk
48
What functions as premotor reflex arc neurons?
Neurons in vestibular nuclei
49
Primary projections of vestibular nuclei target ___, which relays info to ____ and ____.
Thalamic nuclei, cortex (motion/spatial), cerebellum (movement)
50
Secondary projections of vestibular nuclei serve 2 reflexes:
1. Vestibulo-ocular reflex—extraocular neurons 2. Postural reflex—brain/spinal cord
51
Function of vestibulo-ocular reflex
Eye movements that counter head movements
52
What happens to vestibulo-ocular reflex when head is rotated in horizontal plane?
Hair cells in semicircular canal on side toward turning motion are depolarized, hair cells on other side are hyperpolarized
53
In vestibulo-ocular reflex, what do vestibular neurons on the turning side do?
Increase firing, excite neurons in medial vestibular nucleus
54
What gives rise to 6th cranial nerve?
Excitatory fibres from medial vestibular nucleus projecting to contralateral abdomens nucleus
55
Where is the abducens nucleus?
Pons
56
What does the abducens nucleus contain?
Motor neurons and interneurons
57
2 outputs of abducens nucleus:
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
What do inhibitory projections from medial vestibular nucleus to ipsilateral abducens nucleus do?
Prevents excitation of ipsilateral rectus muscle and contralateral medius muscle
59
What is the point of the vestibulo-ocular reflex?
Eyes move to right when head moves to left and vice versa
60
What resets eyes to original position after vestibulo-ocular reflex?
Fast saccade
61
What is physiological nystagmus?
Reflex that counters head rotation
62
How is vestibulo-ocular reflex used clinically?
Tests nerve integrity and connections between nuclei using caloric testing
63
How does caloric testing work?
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
What causes loss of vestibulo-ocular reflex?
Abducens nerve or vestibular system dysfunction
65
What causes asymmetric eye movements?
Oculimotor nerve dysfunction
66
2 major pathways of connections of vestibular nuclei to motor neurons and interneurons:
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
Function of vestibulocervical reflex:
Neck movements that counteract passive head movements
68
Example of vestibulocervical reflex
Head moving forward when falling forward
69
How does vestibulocervical reflex innervate?
Otolith organs send signal to medial vestibular nucleus, which projects to spinal cord motor neurons that innervate neck muscles
70
Function of vestibulospinal reflex:
Body tilts against linear acceleration
71
How does vestibulospinal reflex innervate?
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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