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002 - 6120 - Vet Neurobiology > (10) Vestibular System > Flashcards

(10) Vestibular System Flashcards

1
Q

(Vestibular System)

  1. Responsible for?
  2. Located where (the vestibular apparatus)?
  3. detects what?
  4. relays info where?
A
  1. maintaining normal position of head and eyes as external forces displace the head from normal position
  2. within the inner ear
  3. linear and angular accelerations of head
  4. brainstem nuclei that elicit appropriate postural and ocular responses
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2
Q
  • inner ear is called this because it consists of channels and chamers hollowed out within the temporal bone
  • The labyrinth has what two components?
A
  • the labyrinth
  • osseous and membranous comoponents
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3
Q

What consists of tubes and chambers in the petrous part of the temporal bone?

What does it contain?

A
  • the osseous labyrinth
  • perilymph fluid and house the membranous labyrnth
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4
Q
  1. What are the three osseous components?
A
  1. cochlea; vestibule; semicircular canals
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5
Q

(Three osseous components)

  1. a spiral chamber that is related to hearing
  2. a large chamber adjacent to middle ear
  3. three semicircular channels in bone, each semicircular canal is orthogonal to the other two
A
  1. cochlea
  2. vestibule
  3. semicircular canals
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6
Q
  1. What consists of interconnected tubes and sacs filled with endolymph?
  2. what is endolymph high in?
  3. What is fluid outside membranous labyrinth called? chemical makeup?
A
  1. membranous labyrinth
  2. potassium
  3. perilymph; low in potassium, high in sodium
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7
Q
  1. What important type of cell does the membranous labyrinth contain?
  2. What four components does membranous labyrinth consist of?
A
  1. sense organ receptor cells
  2. cochlear duct; utricle; saccule; three semicircular ducts
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8
Q

(Parts of the membranous labryinth)

  1. cochlear duct - related to what?
  2. utricle - larger or smaller of two sacs? sacs located where? contains?
  3. Saccule - larger or smaller of two sacs? sac located where? contains?
  4. Three Semicircular ducts - each duct is located within what? each duct has an enlargment called what? Which contains what (+define what they are)?
A
  1. hearing
  2. larger, vestibule, macula and otolith membrane
  3. smaller, vestibule, macula and otolith membrane
  4. within one of the semicircular canals; an ampulla; crista ampullaris (crest bearing sensory receptor cells) and a cupula (gelatinous membrane)
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9
Q
  1. What is a collective term for sensory areas withing the membranous labyrinth that are responsible for detecting linear acceleration (including gravity) and angular acceleration of the head?
  2. What three things does the vestibular apparatus (sense organ) consist of?
A
  1. Vestibular apparatus
  2. macula of the utricle; macula of the saccule; crista ampullaris
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10
Q

(Vestibular organ consists of)

  1. sensory area (spot) located in the wall of the utricle. How is it oriented? What does it detect?
  2. sensory spot in the wall of the saccule. detects what?
  3. one per semicircular duct ampulla. each detects what?
A
  1. macula of the utricle; horizontally; linear acceleration in the horizontal plane (side to side)
  2. macula of the saccule; linear acceleration in the vertical plane (up and down)
  3. crista ampullaris; angular acceleration directed along the plane in which the duct is positioned
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11
Q

(Signal Transduction)

  1. Do all components of the vestibular apparatus (each macula and crista ampullaris) have the same kind of sensory epithelium? What is it composed of? What protrude from the apical surface of each hair cell?
  2. What does movement of the overlying membrane cause? Deflection toward the kinocilium does what? What does this allow? Result?
  3. The depolarization (receptor potential) of the receptor cell enables what? What does glutamate trigger?
  4. What does deflection away from the kinocilium do?
A
  1. yes; supporting cells and receptor cells (hair cells); sterocilia protrude into and overlying membrane
  2. deflection of stereocilia; mechanically opens ion channels; allows K+ to flow from endolymph into hair cell; depolarizes receptor cell membrane
  3. Ca++ influx and release of glutamate located along the basolateral region of the receptor cell; action potentials in afferent axons of the vestibular nerve
  4. closes ion channels and reduces glutamate release
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12
Q

(Crista Ampullaris)

  1. What is the gelatinous membrane that stereocilia are embedded in called? When is it moved by?
  2. The direction of head rotation is signaled to the brain by the relative amounts of activity from what?
A
  1. cupula; fluid inertia when the head rotates in the plane of the semicircular duct
  2. From the three semicircular ducts
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13
Q

(Macula)

  1. What are stereocilia embedded in? Why is it called this? Because it is denser than the surrounding endolymph, the otolith has more inertia than what? What does this cause?
A
  1. gelationous otolith membrane; contains calcium concretions (ear stones); endolymph fluid; otolith membrane lags during linear acceleration or deceleration of the head
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14
Q
  1. Are receptor cells spontaneously active? So, what does movement of the stereocilia result in?
  2. Are vestinular organs of each side mirror images? So, a shift toward the kinocilia on one side leads to? What does this mean?
A
  1. yes (vestibular nerve axons continually conduct action potentials to the brainstem); increase or decrease in rate of spontaneous activity
  2. yes; a shift away from the kinocilia on the opposite side; spontaneous activity which bilaterally balanced under normal postural conditions, is quickly imbalanced during head acceleration
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15
Q

(CNS connections)

  1. Vestibular nerve fibers (axons from neuron cell bodies of the vestibular ganglion) travel from where to where? Where do they synapse?
A
  1. from inner ear to the brain; synapse in vestibular nuclei of the brainstem and in the nodulus or flocculus of the cerebellum
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16
Q

(Vesibular Nuclei)

  1. How many vestibular nuclei? where are they?
  2. The nuclei receive input from vestibular nerve and project to what four places?
A
  1. four (located bilaterally so eight sort of); in medulla oblongota and pons

2.

1) cerebellum (flocculo-nodular lobe)
2) reticular formation
3) spinal cord via the lateral vestibulospinal tract (activates limb externsor muscles via aplha and gamma neruons)
4. nuerons controlling eyes (3, 4, 6 cranial nerves) and neck (cervical spinal cord) muscles via the medial longitudinal fasciculus

17
Q

(Vestibular Reflexes)

(Effects on the Eyes)

  1. The eyes are shifted in a direction _____ to the direction that the head is accelerated. In order to do what?
  2. In general, vestibular nuclei push the eyes _____. When nuclear activity is balanced on each side what happens?
A
  1. opposite; to maintain a stable visual field

(For example, head rotation to the right produces increased AP frequency in the right vestibular nerve and decreased frequency in the left. Vestibular nuclei on the right side dominate activity in the left abducens nucleus & right oculomotor nucleus, causing both eyes to move left.)

  1. contralaterally; push is balanced and eyes are not shifted
18
Q

(Effects on Neck and Limbs)

  1. The head is maintained in a normal posture by means of what?
  2. What influences extensor muscles in the limbs? Extensor muscles are contracted on the side _____ which the head is accelerating? To preclude what?
A
  1. vestibular reflex control of neck muscles
  2. the vestibular nuclei; toward; falling
19
Q

(Clinical Considerations)

  1. Lesions affecting what 4 areas are common? What do they produce?
A
  1. middle ear, vestibular apparatus, vestibular nerve, vestibular nuclei; imbalanced neural activity (leads to vestibular syndrome)
20
Q

(Vestibular syndrome)

  1. head tilt - what side is lesion on?
  2. stumbling, falling, rolling - direction is toward or away from lesion side?
  3. Oscillatory eye movement which are abnormal when the animal is not rotating. What is this called? Slow phase of nystagmus is direceted toward or away from the side of lesion.
A
  1. “down ear” side
  2. toward
  3. nystagmus; toward

(Note: You should be capable of diagnosing which side has the destructive lesion. The normal (undamaged) side is more active than the lesioned (damaged) side. This imbalance causes reflexes to be expressed as if there were an “acceleration” toward the normal side, but there is no acceleration so the animal is thrown off balance.)

21
Q
  1. What do you call it when eyes continuously shift; slowly to one side, then quickly back to center?
  2. Which type is generated reflexly by vestibular nuclei in response to angular acceleration?
  3. Which type is generated by cerebral cortex when focusing on moving objects (train passenger focussing on telephone poles)
A
  1. nystagmus
  2. vestibular nystagmus
  3. opticokinetic nystagmus
22
Q
A

002 - 6120 - Vet Neurobiology (23 decks)

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