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Vestibular system

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Western University
Physiology 3120
Tom Stavraky

Human Physiology Monday, November 9, 2009 “Neuro VIII” Vestibular System • Adjacent to the cochlea • Function is to position & orient the head in space • No conscious awareness of vestibular system in everyday life (compared to other sensory systems)  If it fails, can experience. . .  Dizziness  Nausea (ill feeling, vomit)  Vertigo  Essential for everyday life • “Tuned” by the cerebellum, which is adversely affected by alcohol • 2 vestibular system 1. Semicircular system (3 in total at right angles to each other)  Hair cells embedded in the cupula (gelatinous wedge)  Responds to angular acceleration of the head in any direction; NOT head position, NOT angular velocity  As the head turns, the endolymph lags behind due to inertia, and applies pressure to the cupula as it moves • Causes movement of hair cells & increase in discharge of vestibular nerve 2. Otolith organ system (utricle & saccule)  Hair cells can be of different orientations  Has crystals of calcium carbonate embedded in the gelatinous matrix on the hair cells; crystals provide inertia to the system  Detect to (I) linear acceleration, a dynamic stimulus, and (II) gravity, a static stimulus • Transduction of action potential in vestibular system  Large cilia = kinocilium; small cilia = stereo cilia  Record discharge to the VIIIth cranial nerve from hair afferents  When stereo cilia bend towards kinocilia, receptor is depolarized, so get more APs; when kinocilia bend towards stereo cilia, receptor is hyperpolarized, so get fewer APs • The two vestibular responses on either side of the head are complementary (i.e. if one increases, the other will decrease) • Pathway of vestibular information  Vestibular nerve  vestibular nuclei in the brain stem; also get some visual input to the
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