~BN18 vestibular system.ppt

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~BN18 vestibular system.ppt

  1. 1. The Vestibular System Lecture 18
  2. 2. Orientation: The Vestibular System <ul><li>Position & motion of body in space </li></ul><ul><ul><li>critical for adaptive interaction </li></ul></ul><ul><ul><li>largely unnoticed </li></ul></ul><ul><ul><li>except unusual conditions </li></ul></ul><ul><ul><ul><li>motion sickness: nausea, dizziness </li></ul></ul></ul><ul><li>Maintenance of balance & posture </li></ul><ul><ul><li>coordinating body position with other sensory information ~ </li></ul></ul>
  3. 3. Receptors for Orientation <ul><li>Inner ear </li></ul><ul><li>Gravity detectors </li></ul><ul><ul><li>plane of reference </li></ul></ul><ul><li>Mechanoreceptors </li></ul><ul><li>Vestibular Organs </li></ul><ul><ul><li>otocysts </li></ul></ul><ul><ul><ul><li>saccule </li></ul></ul></ul><ul><ul><ul><li>utricle </li></ul></ul></ul><ul><ul><li>semicircular canals ~ </li></ul></ul>
  4. 4. Otocysts <ul><li>Liquid-filled “ear sacs” </li></ul><ul><ul><li>lined with hair cells </li></ul></ul><ul><ul><li>contain otoliths </li></ul></ul><ul><ul><ul><li>“ ear stones : direction of acceleration </li></ul></ul></ul><ul><li>saccule: vertical movement </li></ul><ul><li>utricle: horizontal movement ~ </li></ul>
  5. 5. At rest Direction of gravity tilted Acceleration to right
  6. 6. Semicircular Canals <ul><li>Rotary acceleration </li></ul><ul><ul><li>direction & extent of circular movement </li></ul></ul><ul><ul><ul><li>any direction </li></ul></ul></ul><ul><li>3 fluid-filled canals </li></ul><ul><ul><li>right angles to each other </li></ul></ul><ul><ul><li>1 for each major plane </li></ul></ul><ul><li>Movement causes fluid to circulate </li></ul><ul><ul><li>displaces cupula ~ </li></ul></ul>
  7. 7. Semicircular canals Utricle Ampulla Crista hair cells Cupula
  8. 8. Vestibular Pathway <ul><li>Vestibulocochlear nerve (VIII) </li></ul><ul><ul><li>Some axons directly to cerebellum </li></ul></ul><ul><li>Most axons to medulla </li></ul><ul><ul><ul><li>vestibular nuclei </li></ul></ul></ul><ul><ul><li>cerebellum, spinal cord, medulla & pons </li></ul></ul><ul><ul><li>motor nuclei for eyes (III, IV, & VI) </li></ul></ul><ul><ul><ul><li>compensates for movement of head </li></ul></ul></ul><ul><ul><li>temporal cortex (dizziness) ~ </li></ul></ul>
  9. 9. Vestibular Stimulation <ul><li>Perceive movement in an airplane? </li></ul><ul><ul><li>No, persisting passive movement </li></ul></ul><ul><ul><li>Otoliths, fluid move at same speed </li></ul></ul><ul><li>Vestibular system detects active movements </li></ul><ul><ul><li>changes in rate of motion </li></ul></ul><ul><ul><ul><li>acceleration </li></ul></ul></ul><ul><li>heating/cooling fluid  perception of body motion ~ </li></ul>
  10. 10. Visual Illusions of Movement <ul><li>Self vection </li></ul><ul><ul><li>perceive you are moving, but not </li></ul></ul><ul><ul><li>2 adjacent trains, cars </li></ul></ul><ul><ul><li>restricted visual field </li></ul></ul><ul><ul><ul><li>no background information ~ </li></ul></ul></ul>
  11. 11. Visual Illusions of Movement <ul><li>Postural sway </li></ul><ul><ul><li>visual cues help maintain posture </li></ul></ul><ul><ul><li>illuminated booth, that can sway </li></ul></ul><ul><ul><li>individual sways with surroundings </li></ul></ul><ul><ul><li>no vestibular stimulation ~ </li></ul></ul>
  12. 12. Motion Sickness <ul><li>During passive transportation </li></ul><ul><ul><ul><li>e.g. riding in car, but not when driving </li></ul></ul></ul><ul><ul><li>unusual circumstances </li></ul></ul><ul><ul><ul><li>e.g amusement park rides </li></ul></ul></ul><ul><ul><li>usually not steady motion </li></ul></ul><ul><li>Symptoms: nausea, dizziness, vertigo, cold sweats, hyperventilation ~ </li></ul>
  13. 13. Cause of Motion Sickness <ul><li>Sensory conflict theory </li></ul><ul><ul><li>Mismatch b/n visual & vestibular info </li></ul></ul><ul><li>Treisman (1977): cause of vomiting </li></ul><ul><ul><li>ingestion of natural toxins disrupt visual input & motor coordination </li></ul></ul><ul><ul><li>vomiting adaptive response to inappropriate stimulus: toxins/motion </li></ul></ul><ul><li>Dogs: remove vestibular system </li></ul><ul><ul><li>toxins  no vomiting ~ </li></ul></ul>

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