Systems Physiology II 6010

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Systems Physiology II 6010
Lecture 11 Sensory system Vestibular
Bradley Greger, PhD
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Vestibular Sensation

• Angular and linear acceleration
• Important for balance and movement
• Extremely important for oculomotor control
• Mostly unconscious sensation
• Kids love it

• http//www.youtube.com/watch?vMIBPs-ZCKHw

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Anatomy of the Vestibular System

• Principle structures
• Otolith (ear rock) organs
• Utricle
• Saccule
• Detect linear acceleration (gravity)
• Semi-circular canals
• Three superior, horizontal, posterior
• Ampulla at ends of canals
• Angular acceleration (rotation of the head)

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Detecting Angular Acceleration

• Semi-circular canals
• Roughly orthogonal
• Both ends terminate in utricle
• Ampulla enlargement at the canal-utricle
  junction
• Ampullary crest contains hair cells

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Detecting Angular Acceleration

• Semi-circular canals
• Roughly orthogonal
• Both ends terminate in utricle
• Ampulla enlargement at the canal-utricle
  junction
• Ampullary crest contains hair cells active site
• Rotation of the head causes distortion of the
  cupula by inertia of endolymph
• Cupula distorts hair cells
• Sensitive to 0.5/sec2, displacement of 10nm

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Detecting Linear Acceleration

• Otolith organs
• Active site macula

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Detecting Linear Acceleration

• Otolith organs
• Active site macula
• Utriclular macula is horizontal
• Saccular macula is vertical

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Detecting Linear Acceleration

• Otolith organs
• Active site macula
• Utriclular macula is horizontal
• Saccular macula is vertical
• Macula
• Hair cells
• Gelatinous membrane
• Otoliths (otoconia)
• Inertial of otoliths detects head tilt (gravity)
  and linear accelerations

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Hair Cells

• Kinocilium Stereocilia
• Project into cupula and gelatinous layer
• Axis of polarity
• Kinocilium to smallest stereocilia

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Hair Cells

• Kinocilium Stereocilia
• Project into cupula and gelatinous layer
• Axis of polarity
• Kinocilium to smallest stereocilia
• Aligned so that always facing the Utricle

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Hair Cells

• Kinocilium Stereocilia
• Project into cupula and gelatinous layer
• Axis of polarity
• Kinocilium to smallest stereocilia
• Aligned so that always facing the Utricle
• Bending toward kinocilia depolarizes cell
• Bending away from kinocilia hyperpolarizes cell

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Semi-circular canals

• Work in pairs bilaterally
• Rotation of head to right
• Right side hair cells hyperpolarize
• Left side hair cells depolarize

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Planar Relationship of Canal

• Horizontal canals are coplanar
• Anterior canal coplanar with contralater
  posterior canal
• And Vise versa

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Utricle Hair Cells

• Kinocilium Stereocilia
• Project into cupula and gelatinous layer
• Axis of polarity
• Kinocilium to smallest stereocilia
• Bending toward kinocilia depolarizes cell
• Bending away from kinocilia hyperpolarizes cell

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Utricle Hair Cells

• Kinocilium Stereocilia
• Project into cupula and gelatinous layer
• Axis of polarity
• Kinocilium to smallest stereocilia
• Aligned so that always facing the Striola
• Preferred direction of acceleration

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Central Pathways

• Vestibular gangion
• 20000 bipolar cells
• Vestibulocochlear nerve
• Vestibular nuclei in pons
• Oculomotor nuclei
• Control of eye movements
• Cerebellum
• Adaption of movements
• Spinal cord
• Postural control

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Extraocular Muscles

• Superior Inferior rectus
• Medial Lateral rectus
• Superior Inferior oblique
• Correlate with Semicircular canals

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Axes of Extraocular Muscle Movements

• Medial and lateral rectus mostly linear
• Others non-linear

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Rotational Axes of the Eye

• Horizontal
• Vertical
• Torsional
• All extraocular muscles contribute to all eye
  movements to some extent

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Two Types of Volitional Eye Movements

• Saccades
• Fast, hundreds of degrees per second
• Targeting, move fovea on object of interest

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Two Types of Volitional Eye Movements

• Saccades
• Fast, hundreds of degrees per second
• Targeting, move fovea on object of interest
• Smooth pursuit
• Speed determined by motion of target
• Tracking, keep fovea on moving object of interest

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Oculomotor Neurons

• Action potential firing patterns
• Busts during movement phase
• Sustained firing during fixation
• Increases with eccentricity
• Neural integrator

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Multiple Types of Neurons in Oculomotor System
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Adaptation of Saccades
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The Vestibular Ocular Reflex

• Extremely tight coupling between the vestibular
  and oculomotor systems
• Shake you hand and try to track it
• Cant see the line in your palm well
• Shake you head at the same rate
• No problem to visualize the lines in your palm
• Head and Eye movement perfectly cancel
• Gain Eye/Head

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Nystagmus

• Optokinetic
• End point
• Exacerbated by alcohol
• Pathology
• Anyone feel like getting dizzy (need a spinning
  chair)

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Sensory Motor Loops (again)

• Simple sensory motor (vistibular-oculomotor)
  reflexes controlled in brainstem
• Volition sensory motor loops mediated through
  cortex
• Adaptation of both loops through Cerebellar loop