Vestibular System

Question 1

It receives information from

Answer 1

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

Orientation of our head in space

Question 2

Main functions

Answer 2

Eye movement control
Balance and posture

Question 3

How does it achieve its functions?

Answer 3

By integrating visual, somatosensory and cerebellar information

Question 4

Cerebellum provides

Answer 4

Proprioception

Question 5

Components

Answer 5

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)

Question 6

Vestibulum

Answer 6

Membranous organ found inside the petrous portion of the temporal bone

Question 7

Bony labyrinth

Answer 7

Cortical bone underneath vestibulum

Question 8

Inside the membranous labyrinth, we find

Answer 8

Endolymph

Question 9

Semicircular canals perceive

Answer 9

Rotational info (body, head)

Question 10

Utricle and saccule perceive

Answer 10

Linear acceleration

Question 11

Semicircular canals - elements

Answer 11

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

Question 12

Hair cells - types, function, elements

Answer 12

Type I and type II.

Perceive movement in vestibular system.

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

Question 13

Utricle and saccule - elements

Answer 13

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.

Question 14

How does endolymph move within the membranous cupula and macula?

Answer 14

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

Question 15

Translation to neurological signal

Answer 15

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)

Question 16

Mechanism of horizontal rotation

Answer 16

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

Question 17

Head inclination

Answer 17

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.

Question 18

VIII CN formation

Answer 18

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

Question 19

Depolarization

Answer 19

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)

Question 20

Hyperpolarization

Answer 20

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

Question 21

Vestibular nerve pathway

Answer 21

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

Question 22

Vestibular nuclei - projections that receives are

Answer 22

Topographically organized

Question 23

Sup and Med vestibular nuclei - afferences, projection

Answer 23

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

Question 24

Lat, Med and Inf vestibular nuclei - afferences, projections

Answer 24

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

Question 25

Medial vestibular nucleus - additionally…

Answer 25

Receives inputs from the retina

Question 26

Juxtarestiform body

Answer 26

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

Question 27

Comparator units

Answer 27

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

Question 28

Vestibular networks - formed by

Answer 28

Other afferents that reach, providing information

Question 29

Vestibular networks

Answer 29

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

Question 30

Vestibulo-ocular reflex - function

Answer 30

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

Question 31

Vestibulo-ocular reflex - characteristics

Answer 31

Compensatory (= magnitude of movement, opposite direction) Habituate and eventually cease if prolonged Can be controlled and suppressed

Question 32

Vestibulo-ocular reflex - types

Answer 32

Rotational reflexes Translational reflex Counter-rolling reflex

Question 33

Rotational reflexes takes place when

Answer 33

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

Question 34

Rotational reflexes are

Answer 34

Simple

Question 35

Rotational reflexes are the origin of

Answer 35

Oculocephalic reflex (physiological Nystagmus)

Question 36

Pathological Nystagmus occurs when

Answer 36

Semicircular canals are stimulated while the head is stationary

Question 37

Optokinetic reflex is mediated by

Answer 37

input received from ganglionar cells in the retina.

Question 38

Input to optokinetic reflex …

Answer 38

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

Question 39

Optokinetic reflex result

Answer 39

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

Question 40

Optokinetic reflex characteristics

Answer 40

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

Question 41

Rotational reflexes pathway (say turn the head to left)

Answer 41

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)

Question 42

Translational reflexes

Answer 42

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

Question 43

Counter-rolling reflex

Answer 43

Torsion eye movement

Question 44

Vestibulo-spinal reflexes involve

Answer 44

muscle tone

Question 45

Vestibulo-spinal reflexes generate

Answer 45

Postural adjustments of head and body

Question 46

Vestibulo-spinal reflexes generate main pathways

Answer 46

Lateral vestibulospinal tract Medial vestibulospinal tract

Question 47

Lateral vestibulospinal tract is formed by

Answer 47

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

Question 48

Lateral vestibulospinal tract organization

Answer 48

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

Question 49

Lateral vestibulospinal tract projections excite

Answer 49

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

Question 50

Lateral vestibulospinal tract function

Answer 50

Stabilizing the body (gives corrective movements)

Question 51

Medial vestibulospinal tract function

Answer 51

stabilizing head and neck

Question 52

Medial vestibulospinal tract is formed by

Answer 52

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

Question 53

Vestibulo-cerebellar reflexes

Answer 53

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

Question 54

Vestibulo-cerebellar reflexes connections

Answer 54

Primary, direct, through the juxtarestiform body (w/out passing through vestibular nuclei) Secondary, indirect, from vestibular nuclei to different deep cerebellar nuclei

Question 55

Vestibulo-thalamo-cortical network function

Answer 55

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

Question 56

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

Answer 56

Bilaterally

Question 57

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

Answer 57

Ventroposterolat (VPL) & posteroinf (PI) nuclei —> 1ª somatosensory cortex, area 3a (posture control) Post nuclear group (centromedian & parafascicular nuclei) —> 1ª somatosensory cortex, area 2V.