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Neurobiology > Vestibular System > Flashcards

Vestibular System Flashcards

1
Q

What is the most common origin of vestibular issues causing dizziness?

A

Peripheral vestibular system

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2
Q

What are the components of the outer ear?

A
  • Auricle/pinna
  • Auditory canal
  • Tympanic membrane (boundary between outer ear and middle ear)
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3
Q

What are the components of the middle ear?

A

Ossicles: malleus, incus, stapes

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4
Q

What are the components of the inner ear?

A
  • Cochlea
  • Labyrinth
  • Vestibule (utricle and saccule)
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5
Q

What are the functions of the peripheral vestibular system?

A
  • Maintain postural stability
  • Stabilizing visual images during head movement to allow clear vision
  • Provides information used for spatial orientation (head position relative to gravity)
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6
Q

What is the bony labyrinth?

A
  • Structure in the inner ear made of compact bone
  • Filled with perilymph, which is a fluid similar to CSF
  • Contains membranous labyrinth
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7
Q

What is the membranous labyrinth?

A
  • Structure suspended within the bony labyrinth
  • Filled with endolymph, which is a fluid similar to intracellular fluid
  • Contains the 3 semicircular canals and 2 otolith organs
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8
Q

What are the three semicircular canals?

A
  • Horizontal semi-circular canal
  • Posterior semi-circular canal
  • Anterior semi-circular canal (superior semi-circular canal)

They detect angular acceleration around 3 axes

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9
Q

Describe the horizontal semicircular canal

A
  • Innervated by the superior vestibular nerve
  • Excited with transverse plane movements
  • Right horizontal semicircular canal is excited when turning to the right, left horizontal semicircular canal excited when turning to the left
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10
Q

Describe the posterior semicircular canals

A
  • Innervated by the inferior vestibular nerve
  • Inferior to the anterior semicircular canal
  • Bilateral semicircular canals are excited with posterior sagittal movements (looking up)
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11
Q

Describe the anterior semicircular canals?

A
  • Innervated by superior vestibular nerve
  • Superior to posterior semicircular canal
  • Bilateral semicircular canals are excited with anterior sagittal movements (looking down)
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12
Q

What structures are within the semicircular canals?

A
  • Endolymph
  • Ampulla: widened end of canal
  • Inside ampulla: gelatinous cupula, sensory hair cells (stereo cilia and kinocilia)
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13
Q

How does a semicircular canal become excited?

A
  • Endolymph moves in response to angular head movement and moves in the opposite direction of the perilymph
  • Causes cupula to move thus causing hair cells to move
  • Stereocilia cells are deflected towards kinocilia causing depolarization
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14
Q

How does a semicircular canal become inhibited?

A
  • Endolymph moves in response to angular head movement and moves in the opposite direction of the perilymph
  • Causes cupula to move thus causing hair cells to move
  • Stereocilia cells are deflected away from kinocilia causing inhibition
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15
Q

What is the push-pull mechanism?

A
  • The brain can detect the direction of head movement by comparing the input between the two vestibular systems (left and right)
  • Inputs should be equal and opposite
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16
Q

What is tonic firing rate?

A
  • Occurs when the head is stationary
  • Labyrinth is constantly firing action potentials to the vestibular nuclei
  • We know that our head is still and balanced
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17
Q

What are the otolith organs?

A
  • Utricle (horizontal movement and head tilt) and saccule (vertical movement)
  • Detect linear acceleration
  • Contain maculae
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18
Q

What structures are inside the utricle and saccule?

A
  • Maculae inside that contain otoconia, which are calcium carbonate crystals
  • Hair cells (stereocilia and kinocilia) sit on the medial wall of the saccule and the floor of the utricle
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19
Q

How are utricles and saccules excited?

A
  • Head tilt or acceleration causes a pull on the otoconia (crystals)
  • The pull of crystals causes hair cells to move toward each other causing excitation
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20
Q

What is the vestibular ocular reflex?

A
  • Maintains stability of an image on the fovea of the retina during rapid head movements
  • Eyes move opposite to the head
  • Peripheral vestibular system connects to central vestibular pathways
21
Q

Describe what occurs in the VOR pathway when you shake your head no

A
  • Primary vestibular neurons from the horizontal semicircular canal will synapse in the ipsilateral medial vestibular nuclei
  • Secondary ipsilateral vestibular neurons from the labyrinth travel in the medial longitudinal fasciculus and decussate to the contralateral abducens nucleus
  • The abducens nucleus sends motor neurons to two places : contralateral lateral rectus muscle, cross again to ipsilateral oculomotor nucleus
  • The ipsilateral oculomotor nucleus sends neurons to the ipsilateral medial rectus muscle
22
Q

What direction does each eye move when you turn your head to the right?

A
  • Both eyes move left
  • The right eye adducts via cranial nerve 3 and the medial rectus
  • The left eye abducts via cranial nerve 6 and the lateral rectus
23
Q

What are the extraocular eye muscles, their innervations, and their functions?

A
  • Medial rectus (CNIII): adducts eye
  • Superior rectus (CNIII): looks up
  • Inferior rectus (CNIII): look down
  • Inferior oblique (CNIII): looks up and out
  • Superior oblique (CNIV): looks down and in
  • Lateral rectus (CNVI): abducts eye
24
Q

What is VOR gain?

A
  • The relationship of eye velocity to head velocity
  • Gaze stability with smooth pursuits using eye muscle movements with slower head movements (60 degrees per second) (VOR not solely responsible)
  • The VOR is solely responsible when the head is turned faster than 60 degrees per second
25
Q

What is VOR phase?

A
  • The relationship of amplitude between the eyes and the head
  • If the head moves 10 degrees to the right the eyes should also move 10 degrees to the right
26
Q

True or False
Hair cells of the semicircular canals and otoliths transmit neural discharge to the vestibular nuclei through the vestibular nerve (CN VIII)

A

True

27
Q

Which nerve receives input from the utricle, anterior semicircular canal, and horizontal semicircular canal?

A

Superior vestibular nerve

28
Q

Which nerve receives input from the saccule and posterior semicircular canal?

A

Inferior vestibular nerve

29
Q

What are the four main vestibular nuclei found in the pons/rostral medulla?

A
  • Superior vestibular nuclei: relay for VOR
  • Medial vestibular nuclei: largest of the four, relay for VOR
  • Lateral vestibular nuclei: lateral vestibulospinal reflex
  • Inferior vestibular nuclei: connected to other nuclei and cerebellum
30
Q

Vestibular nuclei make connections between the vestibular system and other structures such as….

A
  • Other cranial nerves via the medial longitudinal fasciculus
  • Flocculonodular node in the cerebellum
  • Vestibulospinal tracts
  • Cerebral cortex
  • Reticular formation for autonomic control and arousal
31
Q

How does the medial longitudinal fasciculus contribute to the vestibular system?

A
  • Connects the medial and superior vestibular nuclei to the ocular nuclei (cranial nerves 3, 4, and 6) for eye muscle control
  • Heavily myelinated tracts that run near midline bilaterally
  • Part of VOR to adjust eyes in response to head movements
32
Q

How does the cerebellum develop reciprocal connections in the vestibular system?

A
  • Information is sent to the vestibulocerebellum (flocculonodular lobes, cerebellar vermis)
  • Adjusts eyes in response to head movement (VOR)
  • Contributes to postural control
  • Influences coordination of limb movements and magnitude of motor response based on vestibular stimuli
33
Q

How does the medial vestibulospinal tract contribute to the vestibular system?

A
  • Signals from the medial and inferior vestibular nucleus descend bilaterally in the medial motor system to terminate in the cervical and upper thoracic cord
  • Controls position of head and neck
34
Q

How does the lateral vestibulospinal tract contribute to the vestibular system?

A
  • Signals from the lateral vestibular nucleus descend in the medial motor system ipsilaterally down the entire cord, terminating in the anterior horn
  • Controls balance
35
Q

How does the cortex contribute to the vestibular system?

A
  • The ventral posterior nucleus of thalamus projects to the parietal association cortex and the lateral temporal junction
  • Controls head and neck position
  • Sends input to corticospinal tracts
36
Q

What is the vascular supply to the peripheral vestibular system?

A
  • Labyrinthine artery, which is a branch of the anterior inferior cerebellar artery
  • The labyrinthine artery divides into the common cochlear artery and anterior vestibular artery
37
Q

What is the vascular supply to the central vestibular system?

A
  • Posterior inferior cerebellar artery: inferior portion of the cerebellar hemispheres and dorsolateral medulla
  • Basilar artery: pons
  • Anterior inferior cerebellar artery: cerebellum, lower pons
38
Q

What inner ear pathologies may cause peripheral lesions?

A
  • Vestibular neuritis (UVH)
  • Benign paroxysmal positional vertigo (BPPV)
  • Meniere’s disease
  • Unilateral or bilateral vestibular hypofunction
39
Q

What pathologies may cause central lesions?

A
  • Head trauma
  • Meningitis
  • Brainstem or cerebellar stroke
  • Multiple sclerosis
40
Q

What impairments can be associated with the vestibular system?

A
  • Vertigo
  • Nystagmus
  • Unsteadiness
  • Postural instability
  • Ataxia
  • Nausea
  • Vision blurring with head movements
41
Q

What is vertigo?

A
  • Illusion of movement
  • The room feels like its spinning
  • Most common cause is a peripheral dysfunction
42
Q

What is light-headedness?

A
  • Feeling faint
  • Can be caused by hypotension, hypoglycemia, or anxiety
43
Q

What is dysequilibrium?

A
  • Sense of feeling off balance
  • May also be due to weakness or somatosensory dysfunction
44
Q

Describe benign paroxysmal positional vertigo

A
  • Due to otoconia is semicircular canals
  • Acute condition
  • Vertigo lasts around 2 minutes or less
  • Can resolve itself over weeks or months but can be quickly treated with particle repositioning maneuvers
  • Symptoms aggravated with to change in head positions
45
Q

Describe vestibular neuritis

A
  • Due to infection
  • Acute condition
  • Sever symptoms for 2-3 days with gradual improvement over 2 weeks
46
Q

Describe Meniere’s disease

A
  • Chronic condition
  • Symptoms last 30 minutes - 24 hours
  • May have hearing loss with bouts of vertigo
  • Tinnitus as wells as a feeling of fullness in the ear
47
Q

Describe central vestibular disorders

A
  • Caused by damage to the vestibular nuclei or to connections in the brain
  • Rarely only see vestibular signs
  • Common symptoms: somatosensory and/or motor loss, double vision, Horner’s syndrome, ataxia, dysarthria, verticality
48
Q

Describe nystagmus for inner ear pathologies

A
  • Delayed
  • Fatiguing of nystagmus, becomes less intense
  • Horizontal or rotary, not vertical
  • Does not change directions
  • Only present when vertigo is present
49
Q

Describe nystagmus for central patholgies

A
  • Immediate or delayed
  • Horizontal, rotary, or vertical
  • May change directions
  • May occur in the absence of vertigo

Neurobiology (15 decks)

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