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Neuro > Vestibular System > Flashcards

Vestibular System Flashcards

1
Q

It receives information from

A

Where we are moving to (linear + angular a of the head)

Orientation of our head in space

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2
Q

Main functions

A

Eye movement control
Balance and posture

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3
Q

How does it achieve its functions?

A

By integrating visual, somatosensory and cerebellar information

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4
Q

Cerebellum provides

A

Proprioception

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5
Q

Components

A

Temporal bone (petrous portion)
Bony and membranous labyrinths
Endolymph (K+) and Perilymph (Na+)
5 components (bilateral and coplanar)
- 3 semicircular canals: 2 vertical, 1 horizontal
- Utricle and Saccule (join with cochlea)

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6
Q

Vestibulum

A

Membranous organ found inside the petrous portion of the temporal bone

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7
Q

Bony labyrinth

A

Cortical bone underneath vestibulum

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8
Q

Inside the membranous labyrinth, we find

A

Endolymph

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9
Q

Semicircular canals perceive

A

Rotational info (body, head)

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10
Q

Utricle and saccule perceive

A

Linear acceleration

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11
Q

Semicircular canals - elements

A

Ampulla: enlargements at the end of semicircular canals

Cupulae: membrane inside ampulla

Cupula: collagenous struct that divides ampullary region and creates compartments -> inside and outside cupula

Endolymph: fills cupula and space surrounding it

Crysta: neuroepithelial elevation inside the cupula where we find Hair Cells

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12
Q

Hair cells - types, function, elements

A

Type I and type II.

Perceive movement in vestibular system.

Stereocilia on apical surface.
Kinocillium (longer hair) on extreme side of apical surface

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13
Q

Utricle and saccule - elements

A

Macula: homologous structure to crysta, contains hair cells

Otolith memb: gelatinous compartment formed by macula

Endolymph: surrounds macula + otolith membrane

Otoconia: Ca crystals on top of otolith memb (makes it + difficult to move)

Striola: indentation along the midline of the otolithic memb, divides HC type I in centre and HC type II in peryph.

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14
Q

How does endolymph move within the membranous cupula and macula?

A

When we move our head one way, endolymph moves the other way.

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15
Q

Translation to neurological signal

A

Position of stereocilia and Kinocilium changes depending on the movement of endolymph.

DEPOLARIZATION: movement towards kinocilium
(K channels open on apical side = K+ influx into HC - depolariz - glutamate release - AP transmission to neurons)

HYPERPOLARIZAT.: movement away from kinocilium
(K channels open on basolateral side = K+ efflux - hyperpolariz = “silencing”, no AP)

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16
Q

Mechanism of horizontal rotation

A

Everytime we move our head to one side:
ipsilateral side = depolarized
contralateral = hyperpolarized
(endolymph displacement)

Same happens w/ vertical SC canals —> 3D spectrum of movement

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17
Q

Head inclination

A

Depending on which sense we incline our head to, cells on one side of striola will depolariz. while others will hyperpol

(Saccule: kinocilium away from striola // Utricle: kinocilium towards striola)

Utricle and saccule in each person —> encoded map for every movement you’ ve made in your life.

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18
Q

VIII CN formation

A

From the basal portion of HC, axons of vestibular branch are formed + join cochlear nerve

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19
Q

Depolarization

A

K channels open on apical side (contact w/ K+ rich med)

K enters the cells -> depolarization -> Ca2+ channels open + Ca entrance -> exocytosis: Glutamate released to neuron terminals -> fire at higher frequencies (basal act)

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20
Q

Hyperpolarization

A

K channels open on basolat side (contact with Na+ rich, K+ poor medium)

K exits the cells into the perilymph = hyperpolarize
No glutamate release = rate of firing is decreased

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21
Q

Vestibular nerve pathway

A

Neuronal bodies in Scarpa’s ganglion -> brainstem -> 4 vestibular nuclei per side (in Pons and Medulla Oblongata)

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22
Q

Vestibular nuclei - projections that receives are

A

Topographically organized

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23
Q

Sup and Med vestibular nuclei - afferences, projection

A

Afferences from SC canals (info about angular movement)
Project to oculomotor nuclei or spinal cord.

24
Q

Lat, Med and Inf vestibular nuclei - afferences, projections

A

Afferences from Utricle and Saccule (linear acceleration info).
Project to cerebellum, reticular formation and spinal cord.

25
Q

Medial vestibular nucleus - additionally…

A

Receives inputs from the retina

26
Q

Juxtarestiform body

A

Projections which go directly from labyrinth to cerebellum, w/out passing through vestibular nuclei

27
Q

Comparator units

A

Reach all the nuclei bilaterally (don’t only get to their destination but everywhere else)
Way of comparison.

28
Q

Vestibular networks - formed by

A

Other afferents that reach, providing information

29
Q

Vestibular networks

A

Vestibulo-ocular network
Vestibulo-spinal network
Vestibulo-cerebellar network
Vestibulo-thalamo-cortical network

30
Q

Vestibulo-ocular reflex - function

A

Allows us to keep our eyes fixed on something as we move
(Keep the image focused on the fovea as we move)

31
Q

Vestibulo-ocular reflex - characteristics

A

Compensatory (= magnitude of movement, opposite direction)

Habituate and eventually cease if prolonged

Can be controlled and suppressed

32
Q

Vestibulo-ocular reflex - types

A

Rotational reflexes
Translational reflex
Counter-rolling reflex

33
Q

Rotational reflexes takes place when

A

We turn our head but want to keep looking in = direction

34
Q

Rotational reflexes are

A

Simple

35
Q

Rotational reflexes are the origin of

A

Oculocephalic reflex (physiological Nystagmus)

36
Q

Pathological Nystagmus occurs when

A

Semicircular canals are stimulated while the head is stationary

37
Q

Optokinetic reflex is mediated by

A

input received from ganglionar cells in the retina.

38
Q

Input to optokinetic reflex …

A

conveys info about movement collected through vision and carries it to oculomotor nucleus

39
Q

Optokinetic reflex result

A

Move extrinsic eye muscles to maintain the image focused on the fovea during movement and recover a clear image.

40
Q

Optokinetic reflex characteristics

A

Slower
Opposed the vestibulo-ocular
Doesn’t habituate and stop working

41
Q

Rotational reflexes pathway (say turn the head to left)

A

Endolymph moves to R: L HSC depolarize & R HSC hyperpolarize —> L vestibular nerve reach sup & med vestibular nuclei + cerebellum through juxtarestiform body

  • Excitatory signal —> ipsilateral oculomotor nucleus (L) = contract L med rectus —> turn eye to R
  • Excitatory signal —> contralateral abducens nucleus (R) = contract R lat rectus —> turn eye to L
  • Fibers —> ipsilateral (L) abducens nucleus = inhibit it (L lat rectus not to contract = med rectus act)
42
Q

Translational reflexes

A

Needed to keep looking a certain object as we move forward
+ complex than the rotational one
Influenced by our distance of the fixed object

43
Q

Counter-rolling reflex

A

Torsion eye movement

44
Q

Vestibulo-spinal reflexes involve

A

muscle tone

45
Q

Vestibulo-spinal reflexes generate

A

Postural adjustments of head and body

46
Q

Vestibulo-spinal reflexes generate main pathways

A

Lateral vestibulospinal tract
Medial vestibulospinal tract

47
Q

Lateral vestibulospinal tract is formed by

A

Fibres descending from lat & inf vestibular nuclei ipsilaterally (ONLY excites ipsilaterally)

48
Q

Lateral vestibulospinal tract organization

A

Topographically organized:
- Rostroventral region —> cervical levels of spine
- Dorsocaudal region —> lumbosacral levels

49
Q

Lateral vestibulospinal tract projections excite

A

Motor alpha & gamma neurons from laminae VII-IX (ant horn grey matter)

50
Q

Lateral vestibulospinal tract function

A

Stabilizing the body (gives corrective movements)

51
Q

Medial vestibulospinal tract function

A

stabilizing head and neck

52
Q

Medial vestibulospinal tract is formed by

A

Fibers descending from sup & med vestibular nuclei bilaterally. Ipsilateral and contralateral projections

53
Q

Vestibulo-cerebellar reflexes

A

Only which provides DIRECT info to cerebellum, fibers from ear to cerebellum

54
Q

Vestibulo-cerebellar reflexes connections

A

Primary, direct, through the juxtarestiform body (w/out passing through vestibular nuclei)

Secondary, indirect, from vestibular nuclei to different deep cerebellar nuclei

55
Q

Vestibulo-thalamo-cortical network function

A

Perception of how we are moving in space = conscious.
Perception of vertical orientation and rotation

56
Q

Vestibulo-thalamo-cortical network nuclei will project to the thalamus

A

Bilaterally

57
Q

Vestibulo-thalamo-cortical network nuclei will reach (once in the thalamus)

A

Ventroposterolat (VPL) & posteroinf (PI) nuclei —> 1ª somatosensory cortex, area 3a (posture control)

Post nuclear group (centromedian & parafascicular nuclei) —> 1ª somatosensory cortex, area 2V.

Neuro (23 decks)

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