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Neuro Final Exam > Vestibular System > Flashcards

Vestibular System Flashcards

1
Q

What are the five components of the vestibular system?

A
  1. peripheral receptor apparatus (inner ear, transduces head motion and position)
  2. central vestibular nuclei (brainstem, integrates and distributes info that controls motor activities and spatial orientation)
  3. vestibuloocular network (vestibular nuclei, control of eye movements)
  4. vestibulospinal network (head movements, axial musculature, postural reflexes)
  5. vestibulothalamocortical network (conscious perception of movement/spatial orientation)
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2
Q

What receptor structures make up the vestibular labyrinth?

A

Three semicircular canals

Two otolith organs

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3
Q

Describe the bony labyrinth

A

the protective shell that houses the fluid-filled system (the membranous labyrinth)

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4
Q

Describe the membranous labyrinth

A

Connecting tubes and prominences that house vestibular receptors

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5
Q

Describe perilymph and where does it exist?

A
  • between membranous and bony labyrinths
  • similar to CSF
  • bathes vestibular portion of CN VIII
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6
Q

Describe endolymph and where does it exist?

A
  • within the membranous labyrinth

- covers sensory receptors of the vestibular and auditory systems

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7
Q

Are ionic concentrations of perilymph and endolymph the same? What is the purpose of this?

A
  • ionic concentrations are different
  • if distribution or ionic content of endolymph is disturbed, often results in vestibular disease
  • balance is maintained by cells in the membranous labyrinth and endolymphatic sac
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8
Q

What kind of motion is received by semicircular canals?

A

Rotational head movements (angular accelerations)

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9
Q

What kind of motion is received by otolith organs?

A

Translational head movements (linear accelerations)

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10
Q

What innervates the receptor cells in vestibular organs?

A

Primary afferent fibers of vestibular (Scarpa) ganglion

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11
Q

Describe the location of the primary afferent fibers that innervate the receptor cells of vestibular organs

A
  • bipolar cells
  • central processes enter the brainstem
  • terminate in ipsilateral vestibular nuclei and cerebellum
  • cell bodies are in the ganglia
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12
Q

Describe the organization of planes of the vestibular organs

A
  • Horizontal SC canal/utricle approx. 30 degrees anterodorsal to the nose (head is pitched down when walking/running, so the plane of these organs becomes parallel with the earth/perpinducular to the gravity)
  • Anterior/Posterior SC canals/saccules are vertical and at right angles to the horizontal SCC/utricle
  • Vertical canals are at right angles to each other, plane of one anterior canal is coplanar with contralateral posterior canal
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13
Q

Describe the blood supply to the labyrinth

A

The labyrinthine artery (branch of AICA)
-enters temporal bone via internal auditory meatus
Sylomastoid artery also provides some branches to the labyrinth (semicircular canals)
Interruption of blood supply compromises vestibular and cochlear function (vertigo, nystagmus, unstable gait)

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14
Q

Describe the anatomical organization of the membranous labyrinth

A
  • supported in the body labyrinth by connective tissue
  • semicircular canal ducts connect to the urticle
  • each duct ends with an ampulla (sensory receptors are in the base of each ampulla)
  • receptors in utricle are longitudinal along the base
  • receptors in the saccule are vertical along medial wall
  • endolymph drains into endolymphatic sinus via endolymphatic duct
  • saccule connected to cochlea by ductus reuniens
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15
Q

Meniere’s Disease

A

Increased endolymph volume, causing distention of membranous labyrinth

  • fluctual hearing loss, vertigo, positional nystagmus, and nausea
  • TX: diuretic and salt-restricted diet, implantation of shunt into swollen endolymphatic sac
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16
Q

Describe a Type I vestibular sensory receptor

A
  • chalice shaped

- surrounded by afferent terminal (nerve calyx)

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17
Q

Describe a Type II vestibular sensory receptor

A
  • cylindrical

- innervated by synaptic boutons

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18
Q

Commonalities of TI and TII vestibular sensory receptors

A
  • hair cells with stereocilia that project from apical surface
  • a single longer kinocilium
  • both receive synapses from vestibular efferents that control receptor sensitivity (activated by behaviorally arousing stimuli or CN V stimulation)
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19
Q

Describe vestibular neuritis

A
  • severe vertigo, nausea, vomiting
  • no hearing loss or other CNS deficits
  • edema of vestibular nerve or ganglion (acute viral infections such as herpes simplex)
  • some have recent history of URI/cold/influenza
  • treat with antiemetics, vestibular suppressants, corticosteroids, and anti-virals
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20
Q

Describe vestibular schwannoma

A
  • benign tumor of Schwann cells of vestibular root (rarely from cochlear root)
  • 5-10% of all intracranial tumors
  • usually in the cerebellopontine angle; inpinges on structures in the internal auditory meatus (CN VII/VIII/labyrinthine artery)
  • slow growing, hearing loss (all cases), gait issues (most), tinnitus (most)
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21
Q

Describe benign paroxysmal positional vertigo

A
  • one of most common vestibular disorders
  • brief episodes of vertigo w/ certain changes in body position
  • turning over in bed, getting up in the morning, bending over, rising from a bent position
  • otoconial crystals from utricle separate from otolith membrane; become lodged in cupula of semicircular canal (abnormal cupula deflections occur)
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22
Q

Describe subjective vertigo

A

the patient feels that they are spinning

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23
Q

Describe objective vertigo

A

the patient feels like the room is spinning

nystagmus beats in the direction opposite to the original direction of rotation

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24
Q

Describe dizziness

A

nonspecific, spatial disorientation that may or may not involve feelings of movement

  • may be accompanied by nausea or postural instability
  • not exclusively a vestibular phenomenon
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25
Q

Describe the ampulla

A
  • hair/supporting cells lie embedded in the crista, goes across the base of the ampulla
  • -TI in the central regions, TII in the peripheral regions
  • enveloped in the cupula (gelatinous structure)
  • cupula allows movement of the stereocilia towards or away from the kinocilium
  • cupula has same specific density as endolymph
26
Q

Describe how the ampulla helps detect motion

A
  1. rotational head movements produce angular acceleration
  2. endolymph is displaced
  3. cupula is pushed to one side
  4. stereocilia is displaced in the same direction
    (if you move your head to the right, the R-sided cells depolarize and activate, while the L-sided cells hyperpolarize and are inhibited)
27
Q

Describe to macula

A
  • Stereocilia extend into the otolith membrane (gelatinous coating)
  • The otolith membrane is covered by otoconia (calcium carbonate crytals)
  • more dense than surrounding endolymph
  • not displaced by normal endolymph movements
28
Q

Describe how the macula helps detect motion

A

changes in head position relative to gravity/linear accelerations (forward/backward or upward/downward) displace otoconia, which bends the underlying hair cell stereocilia

29
Q

What is the function of vestibular nuclei?

A

process positional and movement info for control of visual and postural reflexes
-each nucleus differs in their afferent/efferent connections

30
Q

Describe the location of the superior vestibular nucleus

A

superolateral in central pons

bordered by restiform body and 4th ventricle

31
Q

Describe the location of the medial vestibular nucleus

A

lateral floor of 4th ventricle

rostrocaudal extent

32
Q

Describe the location of the lateral vestibular nucleus

A

lateral to the medial vestibular nucleus

contains large neurons (Deiters)

33
Q

Describe the location of the inferior vestibular nucleus

A

lateral to medial vestibular nucleus

extends through the medulla

34
Q

Describe areas 2v and 3a of the vestibular cortex

A

Primary Somatosensory Cortex

  • stimulation of 2v: sensations of whole body motion
  • 3a integrates motor control of the head and the body
35
Q

Describe area 7 of the vestibular cortex

A

Parietal Cortex

  • spatial coding, visual (optic flow), and vestibular motion signals
  • integrates cues of body motion in space
  • *lesions=confusion in spatial awareness**
36
Q

Describe the insular areas of the lateral sulcus and the parietoinsular vestibular cortex

A

cells respond to body motion, somatosensory, proprioceptive, and visual motion stimuli
lesions cause vertigo, unsteadiness, loss of perception for visual vertical

37
Q

Describe the prefrontal cortex and superior frontal gyrus

A

receives vestibular signals, related to the frontal eye fields
control of saccades and smooth pursuit eye movements

38
Q

Vestibulovestibular Fibers

A
  • arise from all vestibular nuclei
  • most prominent in superior and medial nuclei
  • form reciprocal connections with analogous contralateral nucleus
  • coordinate verious motions of the eyes
39
Q

Spinovestibular Fibers

A
  • arise from all levels of the spinal cord
  • proprioceptive input to medial and lateral vestibular nuclei
  • positional sense related to balance
40
Q

Other input to vestibular nuclei

A
  • reticular formation
  • raphe nuclei
  • thalamus
  • several other cortical regions

maintain balance

41
Q

Primary (Vestibular) Afferent Fibers

A
  • enter at pontomedullary junction

- traverse restiform body and branch into ascending and descending fibers

42
Q

Afferent Fibers from the Semicircular Canals (ampulla)

A
  • project to superior and medial vestibular nuclei

- minor input to lateral and inferior vestibular nuclei

43
Q

Afferent Fibers from the Otolith Organs (maculae)

A

project to lateral, medial, and inferior vestibular nuclei

44
Q

Saccular Afferent Fibers

A

project to contralateral oculomotor nucleus

influence vertical eye movements

45
Q

What is the only sensory organ in the body that sends direct primary afferent projections to the cerebellar cortex and nuclei?

A

Cerebellum

46
Q

Describe the course of vestibulocerebellar fibers

A

Primary vestibulocerebellar fibers travel from the fastigial nucleus through the juxtarestiform body in the inferior cerebellar peduncle
Collaterals are sent to the dentate nucleus and terminate as mossy fibers
Vestibular nuclei send fibers to fastigial and dentate nuclei and secondary vestibulocerebellar projections

47
Q

What is the purpose of the vestibuloocular network?

A

Keeping a fixed gaze on an object while the head is moving

48
Q

How does the vestibuloocular network accomplish its purpose?

A

Vestibuloocular reflex (stabilizing eye movements)

  • compensatory: equal in magnitude and opposite in direction to the head motion
  • occurs for any direction and speed of head motion
  • can be willingly suppressed to focus on a moving target (such as trying to run and catch a ball)
49
Q

Which vestibular receptive organs are associated with vertical movements?

A

vertical SC canals

saccule

50
Q

Which vestibular receptive organs are associated with horizontal movements?

A

horizontal canals

utricle

51
Q

Which vestibular receptive organs are associated with torsional eye movements?

A

vertical SC canals

utricle

52
Q

Describe the pathway of afferent nerves necessary to produce eye movement during head rotation

A
  1. Send axons through the medial longitudinal fasiculus to the contralateral abducens nucleus
  2. Abducens motor neurons excite the ipsilateral lateral rectus muscle via cranial nerve VI
  3. Abducens interneurons send excitatory impulses to contralateral oculomotor nucleus (innervates the medial rectus muscle)
    - a second set of vestibular neurons send excitatory signals to ipsilateral oculomotor nucleus (medial rectus muscle)
    - 3rd set of vestibular neurons carry inhibitory signals to the ipsilateral abducens nucleus
    * *inhibit the abducens muscle on the ipsilateral side of head rotation, activate the abducens on the side contralateral of the head rotation)
53
Q

Describe the pathway of afferent nerves necessary to produce eye movement during a righward head turn

A
  1. The right horizontal semicircular canal activates neurons in the right vestibular nuclei
  2. inhibitory signals from the left vestibular nuclei are decreased via the commissural neurons
  3. Neurons in the right vestibular nuclei excite the contralateral abducens motor neurons
  4. Produces contraction in the left lateral rectus and the right medial rectus muscles
  5. Compensatory leftward eye movement keeps the object of interest in the fovea

matching bilateral commections keep the right lateral rectus and left medial rectus inhibited

54
Q

What is the purpose of the linear vestibuloocular reflex?

A

-way to stay balanced during non-rotational movement

  • side-to-side head motion cause horizontal eye motion in the direction opposite of head movement
  • vertical displacement of the body cause oppositely directed vertical eye movement to stabilize gaze
  • during roll tilts of the head, eyes “counter roll” (torsional eye movement)
55
Q

Describe the phases of nystagmus

A
  1. Slow phase: vestibuloocular reflex moves eyes slowly in opposite direction of head movement
  2. Eye reaches limit of how far it can turn
  3. Fast phase: eyes rapidly move back to the central position (eye moves in same direction as head)
  4. Slow phase begins again

Named for the direction of the fast phase

56
Q

Describe the caloric test

A

Used to test the vestibular layrinth
-warm water induces nystagmus that beats toward the ear into which the water was placed
-cold water induces nystagmus that beats away from the ear into which the water was placed
(COWS)
both ears should give equal responses: unilateral lesion of the vestibular pathway will cause reduced/absent nystagmus ipsilaterally

57
Q

Describe the lateral vestibulospinal tract

A
  • muscle tone and reflexive postural adjustments
  • neurons located in the lateral and inferior vestibular nuclei
  • projects to all levels of ipsilateral spinal cord (anterorostal to cervical, posterocaudal to lumbosacral)
  • fibers travel through the lateral medulla and the anterior funiculus of the SC
  • end on alpha and gamma motor neurons and interneurons to laminae VII-IX
  • collaterals branch to different segments, ensuring coordination of postural control
58
Q

Describe the medial vestibulospinal tract

A
  • muscle tone and reflexive postural adjustments
  • bestibular stimulation on neck nuscles
  • medial bestibular nucleus, with some from interior and lateral vestibular nuclei
  • input from vestibular receptorsm cerebellum, and PCMLS info from the spinal cord
  • fibers bilaterally descend through the MLF and end in laminae VII-IX of the cervical spinal cord
  • neck flecor and extensor motor neurons
  • effects seen in the vestibulocolic reflex (stabilize neck)
59
Q

Neurons from which vestibular nuclei project to the thalamus?

A

All four nuclei project neurons to the thalamus

most terminate in contralateral thalamic nuclei

60
Q

Name and briefly describe the two main nuclei of the thalamus

A

Ventral posterolateral nucleus
Ventral posteroinderior nucleus

respond to bestibular and somatosensory stimulation

61
Q

Describe the thalamic regional representation of vestibular information

A

Thalamic regions represent separate but parallel pathways of vestibular info necessary for processing of motion and body orientation information

Neuro Final Exam (14 decks)

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