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Clinical Medicine III > Vestibular Disorders Part I > Flashcards

Vestibular Disorders Part I Flashcards

1
Q

What is the vascular supply to the Labyrinth

A
  • Labyrinthine artery
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2
Q

Describe the Labyrinthine artery

A
  • Most often branches off the AICA (anterior inferior cerebellar artery)
  • May branch directly off of basilar artery
  • Divides into anterior vestibular artery and common cochlear artery
  • Highly susceptible to ischemia due to lack of collateral anastomotic network
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3
Q

Describe the anterior vestibular artery

A
  • Supplies the vestibular nerve, utricle, horizontal & anterior semicircular canals
  • May become occluded due to cardioembolic source, not often visible on MRA
  • No auditory symptoms
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4
Q

Describe the common cochlear artery

A
  • Main cochlear artery supplies the cochlea
  • Vestibulocochlear artery supplies parts of the cochlea, inferior saccule, & posterior semicircular canal
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5
Q

Describe the posterior vestibular artery

A
  • A branch off of the common cochlear artery (vestibulocochlear artery) which originates from the Labyrinthine artery
  • Supplies the saccule & the posterior semicircular canal
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6
Q

The branches of the labyrinthine artery are independent which means occlusion of one branch only affects the structures supplied by the branch (True/False)

A
  • True
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7
Q

Describe the vestibular nuclear complex

A
  • Superior & medial vestibular nuclei are relays for the VOR
  • Medial vestibular nucleus is also involved in VSR & coordinates eye/head movements that occur together (cervicogenic dizziness)
  • Lateral vestibular nucleus is principle nucleus for VSR
  • Descending/inferior vestibular nucleus has connections to all vestibular nuclei & cerebellum but no primary outflow
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8
Q

Describe the ampulla in the semicircular canals

A
  • Ampulla = enlargement of semicircular canal
  • Hair cells contained in each ampulla & otolith organ convert displacement due to head motion into neural firing
  • Hair cells of the ampullae rest on a tuft of blood vessels, nerve fibers, & supporting tissue called the crust ampullaris
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9
Q

Describe the cupula in the semicircular canals

A
  • Cupula = diaphragmatic membrane that overlies each crest & completely seals the ampulla from the adjacent vestibule
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10
Q

Describe the otoliths

A
  • Consists of the utricle, the saccule, & the striola
  • Striola = separates the direction of hair cell polarization on each side of the otolithic organ
  • Utricle is oriented horizontally
  • Saccule is oriented vertically\
  • Responds to both linear head motions & static tilt with respect to gravity
  • Responds to changes in velocity (acceleration/deceleration)
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11
Q

Describe force related to the otoliths

A
  • Force = Mass x Acceleration
  • Shearing forces of the mass of otoconia on the otolithic membrane in response to acceleration/deceleration cause excitation
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12
Q

Describe the utricular function with head tilt

A
  • Hair cells have a resting firing rate
  • Kinocilia are oriented towards the striola
  • Deflection of the hair cells towards the kinocilia results in excitatory output
  • Deflection of the hair cells away from the kinocilia results in inhibitory output
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13
Q

Coordination of eye movements via the medical longitudinal fasciculus

A
  • Coordination of the 2 eyes is maintained via synergistic action of the extra ocular muscles
  • Requires connections among the cranial nerve nuclei that control eye movements
  • Ex: activate an eye muscle on the right then the medical longitudinal fasiculus (MLF) to convey signal from the right sided nerve to the left oculomotor nucleus, which then activates the corresponding eye muscle on the left to match the action on the right eye
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14
Q

Lists what the eye movement systems include

A
  • Saccades
  • Smooth pursuit
  • Vergence
  • Fixation
  • Vestibulo-Ocular reflex
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15
Q

What is the goal of the eye movement systems

A
  • Goal is to position & maintain similar images on corresponding areas of the retinae in order to sustain fusion during eye, head, & body movements or change in position of the visual stimulus
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16
Q

Describe the eye movement systems

A
  • Coordinated eye movements are under supranuclear control
  • Any type of cooperation b/w the 2 eyes whether sensory or motor necessitates cortical control
17
Q

Common vision problems and symptoms following a Brian injury

A
  • Blurred vision
  • Sensitivity to light
  • Reduction or loss of visual field
  • Headaches with visual tasks
  • Reading difficulty
  • Difficulties with eye movements
18
Q

Lists the extra ocular muscles and their functions

A
  • Medial rectus (MR): adduction of eye
  • Lateral rectus (LR): abduction of eye
  • Superior rectus (SR): primarily = elevation of eye, 2ndy = intorsion/rotes top of eye inward, tertiarily = adduction
  • Inferior rectus (IR): primarily = depression of eye, 2ndy = extortion/rotates top of eye outward, tertiarily = adduction
  • Superior oblique (SO): primarily = intorsion, 2ndy = depression of eye, tertiarily = abduction
  • Inferior oblique (IO): primarily = extorsion, 2ndy = elevation of eye, tertiarily = abduction
19
Q

What is important to know about the extra ocular muscles orientation and direction of pull

A
  • Because of the orientation of the eye in the orbit & the direction of pull of each of the extra ocular muscles, each muscle is capable of producing primary, secondary, & tertiary movements of the eye often seen in combination
20
Q

Types of normal physiologic nystagmus

A
  • Post rotational nystagmus
  • Optokinetic stimulation
21
Q

Describe vestibular nystagmus

A
  • Nystagmus beats to the side of increased neural activity
  • Direction of nystagmus is named for the “fast” phase but the slow component is under vestibular control
  • Fast phase is under central control
22
Q

Describe post-rotatory nystagmus

A
  • If one spins in a chair continuously & stops suddenly the fast phase of nystagmus is in the opposite direction of rotation while slow phase is in the direction of rotation
23
Q

Describe Alexander’s law of nystagmus

A
  • Direction of nystagmus is named for the fast phase
  • In individuals with nystagmus the amplitude of the nystagmus increases when the eye moves in the direction of the fast phase
  • Manifested during spontaneous nystagmus in a patient with a vestibular lesion
  • Nystagmus increases when visual fixation is blocked
24
Q

Describe J.R Ewald’s laws and nystagmus

A
  • Law #1: stimulation of the semicircular canal causes a movement of the eyes in the plane of the stimulated canal
  • Law #2: In horizontal semicircular canals an ampullopetal endolymph movement causes a greater stimulation than an ampullofugal one
  • Law #3: in the vertical semicircular canals the reverse is true
25
Q

Describe the Vestibulo-Ocular Reflex (VOR)

A
  • Head rotates to LEFT
  • Endolymph in LEFT semicircular canal circles to the RIGHT
  • Cupula deflected towards kinocilium
  • Excitatory projections to vestibular nucleus & oculomotor nucleus on LEFT and Abducens nucleus on RIGHT
  • Eyes move to the RIGHT
26
Q

How good does the VOR have to be

A
  • To keep the eye still in space while the head is moving the velocity of eyes should be exactly opposite to head movements
  • Ratio of eye movement to head movement velocity (called the gain) equals -1.0
  • To maintain normal vision retinal image motion must be <2º per second
  • Ex: for a head velocity of 100º per second, the gain of the VOR must be 98% accurate bc any greater error would cause vision to be obscured
27
Q

Describe the head impulse test (Head Thrust Test)

A
  • Clinical test for VOR function
  • Normal function = patient will keep gaze on target
  • Hypofunction = eyes will move with the head (gaze error) which leads to a corrective saccade at the end of head movement
28
Q

Describe cerebellar flocculus and nodulus related to the VOR

A
  • Cerebellar flocculus is required to adapt the gain of the VOR: occurs in response to retinal slip to improve gaze stability
  • Cerebellar nodulus adjusts the duration of VOR responses & is also involved with processing of otolith input: lesion often results in gait ataxia & nystagmus
29
Q

Finding from an H-test

A
  • If H-test is normal = cranial nerves are intact
  • If H-test is normal but one eye is slow to get there = cranial nerves are intact but there is a brainstem issue/lesion
30
Q

Describe cerebellar function related to the VOR

A
  • Cerebellar vermis (Midline) responds to vestibular stimulation: has inhibitory influence on the vestibular nuclear complex
  • Helps to calibrate/modulate vestibular outflow to improve accuracy of vestibular reflexes (VOR and VSR)
  • Lesions to the anterior/superior vermis affect the VSR: profound gait ataxia and truncal instability (excessive ETOH intake)

Clinical Medicine III (20 decks)

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