12 Vestibular

12 Vestibular - VESTIBULAR SYSTEM page 1 AC Brown A7b...

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AC Brown page 1 A7b INTRODUCTION TO VESTIBULAR SENSES A. Located in the inner ear (labyrinth) 1. body labyrinth: cavity within temporal bone 2. membranous labyrinth: two concentric tubes a. space between outer and inner filled with perilymph (similar to CSF) b. inner filled with endolymph (high in K + ) B. Sensory organs of inner ear 1. Cochlea (hearing); innervated by cochlear branch of C.N. VIII 2. Vestibule (orientation and equilibrium); innervated by vestibular branch of C.N. VIII a. Utricle and saccule (2 organs); sense linear movement and gravity b. Semicircular canals (3 canals oriented in mutually perpendicular planes); sense rotational (angular) movement Note: Alternative names for C.N. VIII: Vestibular-cochlear, auditory, acoustic-vestibular SENSORY ENDINGS A. Hair Cells Note: Hair cells cannot generate action potentials but they can depolarize; when depolarized, they release excitatory neurotransmitter to the excitable(1st order) afferent nerve endings at their base B. Sensory response 1. Firing rate of afferent fiber innervating hair cell depends on bending of cilia a. cilia bend toward kinocilium (long cilia) frequency b. cilia bend away from kinocilium frequency 2. Mechanism cilia bend toward kinocilium hair cell K + channels open hair cell soma depolarize
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12 Vestibular - VESTIBULAR SYSTEM page 1 AC Brown A7b...

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