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72 Cards in this Set

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