Module D-09

Question 1

Which cells are the receptor cells of the vestibular and

cochlear divisions of the inner ear?

Answer 1

Hair cell

Question 2

describe hair cell

Answer 2

• The apex of a hair cell is the signal transduction site which contains cilia (mostly stereocilia).
• This area is surrounded by endolymph
• The interior of the cilia is continuous to the cytoplasm of the hair cells.
• At the base of a hair cell we find a synaptic terminal,
  with vesicles containing excitatory transmitter.
• stimulates the afferent fibers of the vestibular and cochlear portions of the vestibulo-cochlear nerve (CN VIII).

Question 3

What differs composition of Endolymph from Perilymph?

Answer 3

Endolymph - high in K+, very low Na+, low Ca2+, slightly
higher Cl-
Perilymph - Very low K+, high Na+

Question 4

Hair cells have ______ potentials not _______

Answer 4

graded; AP

Question 5

Opening of which channels causes depolarization of Hair cells

Answer 5

mechanically gated cation channels (TRPA1 channels)

Question 6

How do the TRPA1 channels open?

Answer 6

Mechanical force produced by a “tip link” between neighboring stereocilia directly opens the cation channels during deflection of the cilia towards the tallest cilium.

Question 7

In what state are the TRPA1 channels when the cilia are at rest ?

Answer 7

the channel is slightly open so there is some influx of K+, so some graded potentials will be seen in the hair cell at rest

Question 8

When will no graded potentials be seen in the hair cell?

Answer 8

when the stereocilia are pointed away from the tallest cilium and the TRPA1 channel completely closes causing hyperpolarization

Question 9

Influx of which ion during depolarization causes transmitter release from the hair cell?

Answer 9

Voltage-gated calcium channels embedded in the hair cell membrane are opened during depolarization, resulting in an inward current of calcium ions in turn, the release of an
excitatory transmitter

Question 10

Which are the 2 types of sensodry organs in the vestibular system?

Answer 10

1) Otolith organs

2) Semicircular canal

Question 11

Which are the 2 otolith organs?

Answer 11

Saccule and utricle

Question 12

describe the otolith organs

Answer 12

• endolymph filled pockets that contain in their walls a patch of sensory hair cells.
• Their cilia support, at their tips, calcium carbonate crystals glued together with a jelly like material (otolithic
  membrane) .
• the cilia of the hair cells have different orientations on each side of the center or striola
• In utricle the kinocilium is oriented towards the striola.
• In the saccule, the situation is just the other way round, with the kinocilium oriented away from the striola.

Question 13

Describe the semicircular canals

Answer 13

endolymph filled pipes which contain a patch of sensory hair cells (crista), with their cilia inserted into a jelly like structure (cupula)

Question 14

Describe how semicircular canals function

Answer 14

When the endolymph moves relative to the walls of
the canals, induced by angular acceleration (rotation) of the head around one of the axes of the semicircular canals, the cupula with the inserted cilia bends,
which leads to depolarization or hyperpolarization of the hair cells.

Question 15

What type of acceleration do otolith organs detect?

Answer 15

Linear acceleration

Question 16

What type of acceleration semicircular canals do detect?

Answer 16

angular acceleration

Question 17

what are the 3 types of semicircular canals?

Answer 17

horizontal, anterior vertical and posterior vertical

Question 18

Describe how otolith function

Answer 18

• When the cilia of the sensory hair cells are tilted, either by gravity forces, or by linear acceleration, the cilia bend, which leads to depolarization or hyperpolarization of the hair cells
• It is dependent on the orientation of the hair cells
• Due to the inertia of the calcium carbonate crystals, the cilia of the hair cells in the one half of the striola are tilted away from the kinocilium (inhibition), while the hair cells in the other half are tilted towards the kinocilium(excitation)

Question 19

What causes the delay in the detection of angular acceleration

Answer 19

The inertia of the endolymph inside the semicircular canal delays its participation in the rotation

Question 20

In the Horizontal semicircular canal the longest cilia are towards __________ and shortest are towards ________

Answer 20

Occipital ; nasal

Question 21

The primary vestibular system works at the __________ level with very little reaching consciousness

Answer 21

Subcortical

Question 22

Is there a cortical primary vestibular area?

Answer 22

No

Question 23

What is the use of vestibular sensory information?

Answer 23

forms the afferent limb of vestibular reflexes (vestibulo-ocular and vestibulo-spinal reflexes).

Question 24

What is the use of vestibular reflexes?

Answer 24

stabilize the eyes and the body when the head moves

Question 25

Describe movement of the endolymph and ampulla in the horizontal semicircular canals when the head is rotated to the left

Answer 25

1) Head rotation to the left induces endolymph flows to the right inside both horizontal semicircular canals 2) The endolymph movement pushes the cupula in the left horizontal semicircular canal towards the back of the head, and the cupula in the right horizontal semicircular canal towards the front (anterior part) of the head. {{{{{{The ampullae of both horizontal semicircular canals are oriented towards the midline; the canals themselves expand more laterally. Within the ampullae, the hair cells are localized in the medial walls, with the kinocilium oriented towards the back of the head. As a consequence, the cilia of the hair cells in the left horizontal semicircular canal are bent towards the back of the head, towards the kinocilium, and they are getting excited. Cilia of hair cells in the right horizontal semicircular canal are Head rotation to the left bent towards the anterior of the head, away from the kinocilium, so they are inhibited. }}}}}}}

Question 26

Describe the state of the horizontal semi-circular canal at rest.

Answer 26

Both horizontal semicircular canal receptor organs are in a neutral state, halfway between maximum excitation and maximum inhibition

Question 27

Movement of the head to the left excites the _____ labyrinth and activates the vestibulo-ocular reflex and the eyes turn to the ______

Answer 27

left; right

Question 28

describe the pathway of the vestibulo-ocular reflex when head is moved to the left

Answer 28

1) The semicircular canals relay the information of head rotation to the vestibular nuclei in the brainstem. 2) Fibers from the excited labyrinth (or the more active semicircular canal receptor organ) which form the afferent limb of the VOR, enter the brainstem at the ponto-medullary junction 3) synapse in the vestibular nucleus. 4) Axons of neurons located in the Vestibular nucleus cross the body’s midline and synapse in the contralateral Abducens nucleus. 5) the abducens nucleus activates the Lateral rectus muscle of the right eye and, via fibers crossing the body’s midline end ascending in the medial longitudinal fasciculus (MLF) the oculomotor nucleus. 6) The oculomotor nerve (CN III) then activates the medial rectus muscle of the left eye. 7) The lateral rectus muscle abducts the right eye and the medial rectus muscle adducts the left eye, so both eyes turn towards the right.

Question 29

Does the Vestibulo-ocular reflex work in the dark?

Answer 29

Yes, it doesn't need visual input

Question 30

Speed of Vestibulo-ocular induced eye movements

Answer 30

up to 300° per second

Question 31

What is Nystagmus?

Answer 31

rhythmically alternating movements of the eyes

Question 32

What are the 2 phases of nystagmus?

Answer 32

1) a slow phase into one direction | 2) a fast phase in the opposite direction

Question 33

What mechanisms drive the slow phase of nystagmus?

Answer 33

driven by a reflex circuitry

Question 34

What mechanisms drive the fast phase of nystagmus?

Answer 34

a simple reset mechanism, driven by the saccadic circuitry

Question 35

The direction of a nystagmus is named after the _____ phase

Answer 35

fast

Question 36

Physiological nystagmus

Answer 36

vestibulo-ocular nystagmus

Question 37

Describe the fast and slow phase of vestibulo-ocular nystagmus

Answer 37

The slow phase of the nystagmus is in the opposite direction of the head movement, and is driven by the vestibulo-ocular reflex. The fast phase (reset) of the nystagmus is in the direction of the head movement, and is driven by a saccade

Question 38

What is the Oculocephalic Maneuver (Dolls eyes maneuver) ?

Answer 38

The examiner turns the head of the patient in the | horizontal (or vertical) plane and notes whether the ocular excursions in the opposite directions occur.

Question 39

What does the Oculocephalic Maneuver test?

Answer 39

Used to determine, whether the vestibulo-ocular reflex pathway from the medulla to the midbrain is intact

Question 40

What is Caloric Testing of the Vestibulo-Ocular Reflex?

Answer 40

procedure the outer ear canal of a patient is irrigated with cold (or warm) water and the examiner observes for conjugate deviation of the eyes, driven by the vestibulo-ocular reflex

Question 41

What happens when cold and warm water are used to irrigate the outer ear?

Answer 41

Cold water => inhibit that Labyrinth and eye moves towards that side Warm water => excites that labyrinth and eye moves to the opposite side

Question 42

Motion sickness aka

Answer 42

Kinetosis

Question 43

What causes Kinetosis?

Answer 43

individuals experience a discrepancy between vestibular and visual inputs

Question 44

How does alcohol intoxication effect vestibular system?

Answer 44

by the interactions of blood alcohol with the endolymph, which can cause convection endolymph flows within the semicircular canals causing Vertigo

Question 45

___________ is an antibiotic that is toxic to vestibular hair cells and should not be used chronically because it accumulates in the ___________

Answer 45

Streptomycin; endolymph

Question 46

Vestibular damage can cause pathological nystagmus where the ____ component gets directed to the damages labyrinth and the ____ component gets directed to the functional side

Answer 46

slow; fast (because it is sensed as inhibition of the damaged side and relative excitation of the normal side)