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22 Cards in this Set

  • Front
  • Back
Sense of balance
require various sensory modalities
-visual, vestibular, neck and limb proprioception
vestibular system
-eye movements, posture, not so much for perception
-requires continuous info about position and motion of all body parts - feedback from head and eyes must be independent since you can move one without the other
-position of head must be based on non-visual cues (hand waving test)
Otolith organs
-saccule and utricle
-head tilt and linear acceleration
3 semicircular ducts
angular acceleration, head rotation

anterior, horizontal, posterior
-filled with endolymph (high K, low Na)
hair cell
-make excitory synapse with the end of a sensory axon from the vestibular nerve (auditory-vestibular nerve VIII)
-20,000 vestibular nerve axons on each side of head.
-cell bodies lie in Scarpa's ganglion
-sensory epithelium in each otolith organ
-hair cells lie among a bed of supporting cells. cilia in gelatinous gap.
Movements are transduced by hair cells when the hair bundles are deflected
-tiny crystals of calcium carbonate
-encrust the surface of macula's gelatinous cap, near the tip of the hair bundles
-key to the tilt sensitivity of the macula
-higher density than surrounding endolymph
-esp. tall cilium of each hair cell
-bending of hair toward the kinocilium ->depolarization excitatory receptor potention
-the other direction of kinocilium ->hyperpolarization and inhibits the cell
Mirror image of saccule and Utricle

When a given head movement excites hair cells on one side, it will tend to inhibit hair cells in the corresponding location on the other
Crista of semicircular canals
a sheet of cells where hair cells of semicircular canals are clustered
-in ampulla
-cilia into gelatinous cupula(spans the lumen of the canal within the ampulla)
Kinocilia of ampulla oriented in the same direction. They all get excited or inhibited together
Semicircular canals have (3)
biphasic receptor potential (Depolarize then hyperpolarize)

Directional sensitivity (structural polarity, functional polarity)

Rapid and robust adaptation
Semicricular canals -rules
1. only hair cells in the same plane as the rotation will be active. Hair cells in semicircular canals orthogonal to the rotational plane will produce little endolymph mov. and little to no response
2. When head turns(rotational accel) the inertia of the endolymph in the canals produces a force across the cupula distending it way from the direction of head mov. Post-rotationally endolymph moves in oppsite direction. Biphasic receptor potential
3.Head turning will evoke oppsite effects on oppsite sides of head because movements of endolymph deforms cupula in opposite directions on each side and because HCs have directional sensitivity
4.Each canal works in concert with a partner on the other side of head. Of the two members of the paif the member on the side to which the head is turning shows increased activity immediately upon turning. In contrast, its partner will be the one most stimulated post-rotationally
5. Linear acceleration of the head produce equal forces on both sides of cupula so hair bundles in canals are not displaced
Central vestibular pathway:

Medial vestibular nucleus
Medial and superior-afferents from semicircular ducts, axons in medical vs tract.
Facilitatory effect on apinal cord neck neurons
maintenance of head position and eye movement

Semicircular canal->scarpa's ganglion->cranial nerve 8, to medial vs nuclus ->Medial longitudinal fasciculus
1. Extraocular motor neurons (3,4,6)
2. Neck motor neurons
Central vestibular pathway:

Lateral vestibular nucleus
afferents from utricle, sends axons in lateral vs tract to spinal cord
facilitatory effect on antigravity muscles enabling upright body posture

Utricle->scarpa's ganglion->cranial nerve 8->lateral vs nuclues
1. cerebellum (assist in motor coordination)
2. Limb motor neurons (vestibulospinal tract)
vestibular afferent have cell bodies in scarpa's ganglion
These join with axons from spiral ganglion to constitute the vesticulocochlear nerve.
Vestibular nucleus also send info to S1 and M1 in cortex
Vestibular Oculomotor Reflex(VOR)
Head turning LEFT-eyes turn right
1.L vestibular n activated
2.activates R abducens n.(6)
3.contract R lateral rectus muscle
4.L abducens n(6) activates L oculomotor nu(3) by L medial longitudinal fasciculus
5.activates L medial recti

6.L vestibular n. activates L oculomotor n(3)->contract L medial recti

7. L vestibular n. inhibit L abducens n(6) which activates R medial recti and L lateral rectus muscle
Nystagmus-eye reflex
-movement of the eyes resulting from the stimulation of the hair cells in the semicircular canals.
-constists of a rapid movement in one direction followed by a slow movement in the opposite direction
-fast-opposite direction of the spin
Support rxn
vertigo-perception of falling

support rxn-opposite of vertigo
Head rotate Right
forward 30

support rxn
-use horizontal canals
-when stopped, body feels like rotating L

nystagmus-L(fast) R(slow)
support rxn-R
Head rotate Right
R shoulder 90

support rxn
-use P and S canals

nystagmus-Down(fast) Up(slow)
past-pointing-Up to the right
support rxn-Back