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72 Cards in this Set
- Front
- Back
What is the purpose of the vestibular system?
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To respond to linear and angular accelerations of the head.
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What does this acceleration information provide information about?
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Head position and movement.
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3 General Components of the Vestibular apparatus:
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-Semicircular canals
-Fluids -Receptors |
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What components of the vestibular apparatus tell the brain about LINEAR accelerations?
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Utricle + saccule
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In what position is the Saccule?
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Dorsal-ventral
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In what position is the Utricle?
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Lateral
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What component in both the utricle and saccule contains the receptors for detecting linear accelerations?
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the MACULA
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What components of the vestibular apparatus tell the brain about ANGULAR accelerations?
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Semicircular canals
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What component of the semicircular canals contains the receptors?
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CUPULA
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What are the receptors in the cupula and macula?
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Hair cells
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What are the receptive components of hair cells?
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kinocilium - the tallest on the end
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What happens when stereocilia are bent toward the kinocilia?
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Depolarization of the hair cell
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What happens if the stereocilia are bent away from the kinocilia?
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hyperpolarization
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What do the saccular and utricular maccules contain?
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Otolith
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What is otolith?
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A heavy fluid (high specific gravity containing CaCO3
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How does otolith achieve sensation of linear displacement?
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When the head tilts, the heavy fluid is acted on by gravity so it flows over hair cells and bends them in a certain way.
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What macular otolith responds to head tilting back/forth?
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Saccule
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What otolith/maccule responds to head tilting side to side?
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Utricle
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What layer over the hair cells moves simultaneously with otolithic displacement?
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otoconia
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In addition to telling about head accelerations what do the saccule and utricle detect?
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Static positions of the head.
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How many semicircular canals?
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3 - lateral, anterior, posterior
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Semicircular canals give information about:
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Angular acceleration
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Component of semicirc canals that contains receptors:
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Cupula
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What does the cupula contain?
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-Hair cells
-Endolymph |
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How does endolymph compare to otolith?
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-Same sp gravity
-No CaCO3 |
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What is the ampulla?
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The interior of a canal
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What happens to hair cells when bent forward?
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Hyperpolarization
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What happens to hair cells when they bend back?
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Depolarization
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What causes the hair cells in right lateral semicircular canals to move back?
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Moving the head to the right
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What is the effect on hair cells in the left lateral semicircular canals when you move your head to the right?
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They move forward, so hyperpolarize.
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So the initial response of endolymph to head movement is:
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To resist movement due to its inertia.
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What happens to endolymph as you keep moving your head?
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it moves with your head.
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What happens when you stop moving abruptly?
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Endolymph Fluid continues to move but your head stops so hair cells hyperpolarize on right as they depolarize on left
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What do we call it when you stop rotating to the right suddenly?
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Left nystagmus
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Pneumonic for nystagmus:
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COWS
Cold = opposite nystagmus Warm = same nystagmus |
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What does putting cold in the right ear do?
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Causes right ear hair cells to hyperpolarize and left ear hair cells to depolarize - like you're turning to the left.
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So the firing in the vestibular nerve fibers depends on:
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The direction in which hairs are bent.
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Result of bending hair cells toward the kinocilium:
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Depolarization and increase rate of firing in afferents.
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Bending away from the kinocilium:
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Hyperpolarization and Decreased rate of firing in afferents.
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Why do the vestibular hair cells allow sensation of static position?
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Because they are constantly firing at rest.
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How do the hair cells in the vestibular apparatus transmit their impulses to the CNS?
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By releasing neurotransmitters in graded ways onto bipolar axons in the vestibular part of CN VIII
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Where does the afferent information from hair cells go first?
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To the vestibular ganglion
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Where does info go from the vestibular ganglion?
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Via central processes constituting CN VIII to the vestibular nuclei.
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Where are the vestibular nuclei located?
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In the medulla
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What do the vestibular nuclei do with information about static postition and acceleration?
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They DISTRIBUTE that information to a very widespread array of efferents in the neuraxis.
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What makes the vestibular system unique?
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It has a more widespread distribution of efferents in the neuraxis than any other special sensory system!
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How many efferents do the vestibular nuclei have?
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8 - EIGHT!!!
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What is the function of the Vestibulospinal tract efferent?
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To influence motorneurons to the EXTENSOR muscles (extend leg to catch your balance if you trip)
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Why do vestibular nuclei have efferent motor neurons to innervate the neck muscles?
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To coordinate head movments with the eyes moving.
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How else do the vestibular nuclei control eye tracking?
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By having efferents to the eye muscle nuclei.
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How do the vestibular nuclei coordinate processing of vestibular information from both sides?
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Both have efferents to each other
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What vestibular efferent is employed when you nod your head in class and it wakes you up?
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Reticular formation
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What vestibular efferents allow conscious processing of vestibular input?
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Thalamic projections to the cortex areas 3a and 2v
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What role does the hypothalamic efferent of vestibular nuclei have?
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Motion sickness
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What IS nystagmus? (define)
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Normal rythmic involuntary oscillations of the eyes - alternating slow and rapid OCULAR EXCURSIONs
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2 types of nystagmus:
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-Optokinetic
-Vestibular |
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What is Optokinetic nystagmus?
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That induced by moving stimuli across the visual field
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What is vestibular nystagmus?
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Nystagmus induced by MOVEMENTS OF THE HEAD.
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How do the eyes move in vestibular nystagmus? Why?
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Against the direction of head movmenet, to preserve gaze (keep it fixed).
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What is the function of normal nystagmus?
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To hold images steady on the retina while the body is spinning.
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What is the purpose of the caloric test?
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To test for unilateral vestibular function.
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What is the basis of the caloric test?
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Pouring cold water in a right ear that is tilted to 30' (to make the lateral canal horizontal) will cause nystagmus in the left direction.
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What happens if you pour warm water in the right ear?
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It causes nystagmus in the right direction.
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What is the physical effect that causes nystagmus in caloric testing?
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Convection currents
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What would happen if the patient laid on his STOMACH and you did caloric testing?
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Nystagmus would be OPPOSITE:
Cold - same direction Warm - opposite direction |
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Why is nystagmus flipped when the patient lies on their stomach versus back?
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Because convection currents are dependent on gravity
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What if there were no gravity?
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No nystagmus would be seen.
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Why does drinking alcohol give the sensation of spinning?
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ETOH has a light spcf gravity; when intake is excessive it gets into the endolymph; causes much more increased sensitivity to movements and takes longer for fluid to stop moving (less inertia).
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What causes vertigo?
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Damage to the vestibular apparatus on one side of the head.
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What is vertigo?
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Movement of the eyes ALONG WITH the head when it rotates due to lack of compensitory eye fixing.
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How does the world appear to move in patients with vertigo?
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Away from the side of the lesion
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When patients with vertigo rotate to the left, what is their sense of rotation?
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To the right.
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