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Transcript of 1 a&p-vestib
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Anatomy and Physiology of
Balance
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Vestibular Hair Cells
• Type I
(aka inner)
• Type II
(aka outer)
With Kinocilium
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The Semicircular Canals
• posterior canal shares plane with contralateral anterior canal.
• horizontal canals share plane.
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Stimulated by Angular Acceleration
• greatest when fulcrum is within head
• induces relative motion of endolymph
• crista is displaced by fluid motion
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Responses of the Cristae
• All kinocilia are oriented in the same direction
• Crista in each pair of canals respond inversely to each other
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The Otolithic Organs
Saccule: roughly
vertical orientation,
responds to acceleration components within saggital plane
Utricle: horizontal (+ 30 deg.) orientation
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Excitation Patterns in the Utricle
STRIOLA
Posterior
Anterior
Medial
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Cranial Nerve VIII
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Vestibular Portion of C.N. VIII
superior division: utricle, anterior part of saccule, and horiz & anterior canals
inferior division: posterior part of saccule, and posterior canal
• to vestibular nuclei
• to cerebellum
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Vestibulocochlear Nerve
• Exits temporal bone near its medial edge.
• Enters lateral face of brainstem at the level of the lower pons.
• Synapsing in (Cochlear and) Vestibular Nuclei
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Responses of Vestibular Neurons:
• To changes in acceleration, but onset and fade slowly
• For most normal head movements firing rates are in phase with head VELOCITY.
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Other inputs to vestibular nuclei:
• Cerebellum: primarily inhibitory
• Spinal cord
• Pontine reticular formation
• Contralateral vestibular nuclei
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From the Vestibular Nuclei:
• Vestibulo-Oculomotor Pathways:
– Direct: to oculomotor nuclei.
– Indirect: via reticular formation to oculomotor nuclei (III IV and VI)
• Vestibulo-Spinal Pathways:
– Lateral V-S-throughout spinal cord
– Medial V-S-cervical & thoracic
– Reticulospinal tract-via brainstem reticular formation
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Median Longitudinal Fasciculus
• A tract linking Vest. Nuclei to nuclei of CN III, IV, & VI;
• Supports conjugate eye movement during movement of the head.
• Continuous with the medial vestibulospinal tract.
• The mlf runs near midline ventral to ventricle IV and the periaqueductal gray matter of the midbrain
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In the brainstem
• Vestibular inputs undergo integration
• Integrated signal is combined with original (velocity driven) signal
• Processing to reset spatial map for eye musculature
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Integration & “Leaky” Integration
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The VOR
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Central Nervous System Will Adapt to Peripheral Damage
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Eye Movements
• Saccades—rapid shift in gaze
• Pursuit—stabilize image of moving object
• Fixation—stabilize image of still object
• VOR—stabilize image during head motion
• OKN—backup for when VOR decays to cont’d head rotation
• Vergent movements—change depth of focus
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Pause cells inhibit
Burst Neurons
which stimulate:III & VI (horizontal)
or
III & IV (vertical)
Saccades
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VisualSystem
VestibularSystem
Somato-Sensation
Compare, Select& Combine Senses
SENSORY INPUTSSENSORY INPUTSVisionVision
VestibularVestibularSomatosensorySomatosensory
SENSORY INPUTSSENSORY INPUTSVisionVision
VestibularVestibularSomatosensorySomatosensory
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Somato-Sensation
Compare, Select& Combine Senses
SOMATOSENSORY SOMATOSENSORY RECEPTORSRECEPTORSSOMATOSENSORY SOMATOSENSORY RECEPTORSRECEPTORS
JointsJointsPositionPosition
KinesthesiaKinesthesia
MusclesMusclesLengthLengthTensionTension
SkinSkinTouchTouch
PressurePressure
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VisualSystem
Compare, Select& Combine Senses
CentralCentralOrientationOrientationNavigationNavigation
PeripheralPeripheralMotion-sensitiveMotion-sensitive
Body-swayBody-sway
VISUAL VISUAL RECEPTORSRECEPTORS
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VestibularSystem
Compare, Select& Combine Senses
Semi-circular canalsSemi-circular canalsOrientationOrientationNavigationNavigation
Utricle & SacculeUtricle & SacculeHorizontal & verticalHorizontal & vertical
acceleration & decelerationacceleration & deceleration
VESTIBULAR RECEPTORSVESTIBULAR RECEPTORS
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Selection based onAvailability AccuracyValue for the task at hand
Processing of inputs from the periphery
SENSORY ORGANIZATIONSENSORY ORGANIZATION
Compare, Select& Combine Senses
Determination of Body Position
Visual Vestibular Somatosensory
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Functional Balance:
Navigating in our
Environment
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A Quiz
Vestibular Pathways Quiz