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The Vestibular System

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An introductory lecture on the anatomy and physiology of the vestibular system.

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The Vestibular System

  1. 1. The Vestibular System Csilla Egri, KIN 306 Spring 2012 Will Ferrell and Jon Heder are challenging their vestibular systems
  2. 2. Outline  Vestibular system  Function  Structure  Semicircular canals  Sensory transduction  Otolith organs  Vestibular pathways  Vestibular reflexes 2
  3. 3. Vestibular System: Function 3  Detects angular and linear acceleration  Important in maintaining balance, posture, and vision  Connections with brainstem, cerebellum, and somatic sensory cortices to provide info about the motions & position of the head & body
  4. 4. Vestibular System: Structure 4
  5. 5. Vestibular System: Structure 5 utricle saccule Otolith organs
  6. 6. Semicircular canals: structure 6  each semicircular canal contains an ampulla  Contains hair cells embedded in sensory epithelium called crista ampullaris  Cilia of hair cells project into gelatinous cap called cupula Enlargement of ampulla Crista ampullaris Semicircular canals
  7. 7. Semicircular canals: function7  Specialized for responding to rotational acceleration of the head  Head rotation results in intertial movement of endolymph in opposite direction  Bends cupula which bends hair cells  Same mechanical/electrical coupling as in auditory hair cells  Excites/suppresses release of NTs from hair cells depending on direction of movement B&B Figure 13-18
  8. 8. Semicircular canals: sensory transduction8 B&L Figure 8-26  Steriocilia maintain directionality on both sides of the head  Bending towards kinocilium  opens mechanically gated cation channels  K+ influx  depolarization  Bending away from kinocilium  closes channels that are open during resting state  hyperpolarization
  9. 9. Semicircular canals: sensory transduction9 Kandel Figure 40-7  Paired canals work together to signal head movement  With turning of the head, hair cells on one side of the body send excitatory signals to the brain while hair cells on the opposite side are inhibited
  10. 10. Otolith Organs: Structure 10  Two otolith organs; utricle and saccule  Each contains a sensory epithleium called the macula  Horizontally oriented in utricle  Vertically oriented in saccule  cilia of hair cells embedded in gelatinous otolithic membrane  Embedded on surface are calcium carbonate crystals called the otoliths otoliths
  11. 11. Otolith Organs: Function 11  Specialized to respond to gravity and linear acceleration  Otoliths have a higher density than endolymph  Shift when angle of head changes  Causes otolithic membrane to shift in same direction  Cilia of certain hair cells deflected  Excites/suppresses release of NTs from hair cells depending on orientation of cilia
  12. 12. Otolith Organs: Function 12  kinocilia of each hair cell are oriented in different directions in relation to striola  Utricle: towards striola  Saccule: away from striola striola
  13. 13. Otolith Organs: Function 13  Same sensory transduction as semicircular canals  Bending of cilia towards kinocilium depolarizes the hair cell Kandel Figure 40-3 otoliths Is this a picture of a macula from the utricle or saccule?
  14. 14. Vestibular Pathways 14  vestibular afferents synapse on vestibular nuclei located in medulla & pons  Nuclei integrate information from vestibular, visual, and somatic receptors and send collaterals to  1.cerebellum  Sends corrective adjustments to motor cortex: maintenance of balance and posture
  15. 15. Vestibular Pathways 15  2.nuclei of cranial nerves  Control coupled movements of the eyes, maintain focus and visual field  3.nuclei of accessory nerves  Control head movement and assist with equilibrium
  16. 16. Vestibular Pathways 16  4.ventral posterior nucleus of thalamus and vestibular area in cerebral cortex (part of primary somatosensory cortex)  Conscious awareness of the position and movement of head Areas 1,2,3
  17. 17. Vestibular Reflexes 17 Vestibulospinal Reflexes  Senses falling/tipping  contracts limb muscles for postural support Vestibulocollic Reflexes  acts on the neck musculature to stabilize the head if body moves Vestibulo-ocular Reflexes  stabilizes visual image during head movement  causes eyes to move simultaneously in the opposite direction and in equal magnitude to head movement
  18. 18. Vestibulo-Ocular Reflex (VOR) 18 Example: head movement to the LEFT 1. inertia of endolymph movement to the right in horizontal vestibular canals causes: a ’d firing of left vestibular afferent b ’d firing of right vestibular afferent 2. Excitatory connections with contralateral abducens nuclei and inhibitory connections to ispilateral side 3. Excitatory connection to inhibitory interneuron in contralateral vestibular nuclei 4. Movement of the eyes to the right abducens nuclei occulomotor nuclei vestibular nuclei B&L Figure 9-
  19. 19. Objectives After this lecture you should be able to:  Relate the anatomical organization of the semicircular canals and otolith organs to sensation of movement/acceleration  Describe the mechanism of sensory transduction in these structures  Outline the vestibular pathways and projections to various brain regions  Describe the pathway of the horizontal vestibulocular reflex 19
  20. 20. 20 1. What specific part of the vestibular system would sense 1. Movement in an elevator 2. Abrupt stop of a moving vehicle 3. Shaking your head side to side 2. In the utricle, if hair cells bend away from the striola, will this cause depolarization or hyperpolarization of the receptor? 3. Based on what you know about the vestibular system, if you spin around for 5-10 seconds, why do you feel dizzy even after you stop? Test your knowledge

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