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Flashcards in Vestibular System Transduction Deck (21)
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1
Q

What are the vestibular sensory organs in the mammal?

A
  • Utricle and saccule and three ampullae of the semicircular canal
    • The vestibular appartus consists of a series of fluid-filled sacs and ducts
2
Q

Where are these sensory organs in the brain?

A
  • Enclosed in the connective tissue of the membranous labyrinth
    • The labyrinth is encased by the bony labyrinth with the petrous portion of the temporal bone
3
Q

The otolith organs detect what kind of movement? The semicircular canal organs?

A
  • Otolith - detect linear acceleration

* Semicircular canal - angular accelerations

4
Q

The two horizontal canals act together to form what signal?

A

• Horizontal rotation of the head

5
Q

The contralateral pairs of anterior and posterior canals signal what?

A

• Read rotation vertically

6
Q

What is the maculae?

A
  • The sensory epithelia of both otolith organs
    • The utricle lies at the floor of the vestibule while the saccule hangs vertically on the laterall wall of the vesibule
    • Together they act as static receptors and signal postural changes
    • The otoconia give additional mass and inertia to the jelly-like load on the hair cell bundle and act to reflect changing orientation of the hair bundle with respect to gravity
7
Q

Endolymph is a special body fluid why?

A
  • High extracellular potassium, low extracellular sodium

* The opposite of blood or other extracellular fluids

8
Q

How does the vestibular hair cell depolarize?

A
  • Mechano-transduction

* The stereocilia move and that physically pulls open a NSC channel

9
Q

What is the kinocilium?

A

• The tallest cilium on the apical surface of the vestibular hair cell

10
Q

What environments are the vestibular hair cells surrounded by?

A
  • Apical part = endolympth
    • Base of hair cells = perilymph
    • The stereocilia are on the apical side
11
Q

Afferent nerves from the vestibular system have what kind of tone at rest?

A
  • They have a tone is the important part
    • There is a resting AP frequency
    • Depolarization of the hair cell increases the frequency of AP by NT release
    • Hyperpolarization decreases NT release and decreases the AP of afferent vestibular nerves
12
Q

How does hyperpolarization of the vestibular hair cell happen?

A
  • If the cilia are pulled against the cell’s polarity it hyperpolarizes the cell
    • The polarity of the cell is in the direction of the kinocilium (from shortest to tallest cilia)
13
Q

The saccular hair bundles project what way and what does that mean?

A
  • Horizontally, allowing them to detect displacement vertically
    • Riding an elevator
14
Q

Utricle hairs project how and sense what?

A
  • Project vertically and detect head tilt forward and back

* Position of head relative to gravity

15
Q

What is the orientation of the cilia in the anterior, posterior and horizontal semicircular canals?

A
  • Anterior +posterio = away from utricle
    • Horizontal = toward utricle
    • The cupula is a gel-like substance that houses the projecting hair cell cilia
    • Thus, when endolympth moves around the cupola will deflect all cilia in the same direction
    • The cupola lives in the crista and the crista is specific for each ampula (each semicircular canal has its own ampula)
16
Q

What is the consequence of inertia on the cupola?

A
  • Acceleration (angular rotation) through the semicircular canal will deflect endolymph one way (opposite of head movement) at first
    • Any endolymph movement deflects the cupola
    • If the rotation is constant velocity the cupola will go back to neutral as endolymph catches up
    • When you stop the movement it sloshes the other way, again deflecting the cupola
17
Q

What is so important about the two sides of the vestibular system acting together?

A
  • The brain takes both information sets into account and doesn’t think it’s normal unless there are both information sets present
    • Vestibular nerve dysfunction manifests as a sense of rotation because there isn’t the balance of both sides creating an overall picture
18
Q

Trace the vestibular afferents to the cortex

A

• Vestibular afferent nerves have cell bodies in the Scarpa’s ganglion
• Project to the ipsilateral vestibular nuclei located at the border of the caudal pons and rostral medulla
• There are four major vestibular nuclei
○ Superior, lateral, medial, inferior
• There is a large mix of afferent information at each of the nuclei
• Visual and auditory system also contribute
• There is also a large variance in the directionality of the second order neurons to the cortex
• SOME primary vestibular afferent that project directly to the flocculo-nodular lobe of the cerebellum

19
Q

Where do the semicircular canals project?

A
  • Mainly to the medial and superior vestibular nuclei
    • These cells give rise to the medial longitudinal fasciculus that carries information to the oculomotor nuclei
    • Combined with mononeurons to neck musculature the longitudinal fasciculus tract becomes the medial vestibulospinal tract
    • Coordination of eye movements and head movements
20
Q

Where do utricles send afferents?

A
  • Lateral vestibular nucleus
    • Medial and inferior nucleus too
    • Lateral nucleus also receives spinal and cerebellar input
    • Axons from this nucleus make up the descending lateral vestibulospinal tract
    • Activation of fibers in this tract will lead to excitation of extensor muscles of the limbs and so participate in the postural reflexes associated with utricular sensation of gravity
21
Q

Where do the saccule, utricle and semicircular canals all project to?

A
  • Inferior vestibular nucleus
    • Also recieves spinal and cerebellar input and in turn projects to the vermal cerebellum
    • Sends output to the reticular formation and other brainstem centers too

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