Lecture8_hearing_vestib -...

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http://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Spinal_cord_tracts_-_English.svg/800px-Spinal_cord_tracts_-_English.svg.png Loss of contralateral pain & temp, plus ipsilateral proprioception (cerebellar); No loss of discriminative touch Loss of contralateral pain & temp, plus ipsilateral proprioception (all kinds) and discriminative touch Loss of bilateral proprioception (all kinds) and discriminative touch, no loss of pain & temp Impairment caudal to injury:
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Neural crest reporter expression in melanoma. Charles K. Kaufman et al. Science 2016;351:aad2197 The surface ectoderm (blue area) grows into skin, hair, nails, cornea, tooth enamel, while the neural plate (brown area) grows into the nervous system. During embryonic development, stem cells near the neural plate express a gene called crestin that probably drives them to divide into neural progenitor cells.
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Hearing and Vestibular Senses
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The Outer, Middle, & Inner Ear OUTER EAR GATHERS SOUND WAVES FROM THE ENVIRONMENT
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The Middle Ear Sound waves enter the ear canal and vibrate the tympanic membrane (eardrum) The vibrational force is transferred to three tiny bones called ossicles: Malleus (or hammer) is attached to the tympanic membrane Incus (or anvil) forms a lever-arm joint with the malleus Stapes (or stirrup) taps against a soft membrane in the cochlea wall called the oval window The ossicles transfer the force of the tympanic membrane’s vibration into vibrations of the membrane of the oval window , sending waves of vibration into the fluid that fills the cochlea Tympanic reflex : there are two muscles (tensor tympani and stapedius) that can damp the vibrations of the middle ear in response to loud sounds, to protect the ear from damage and adjust the gain of hearing The round window provides a “release valve” for increases in cochlear fluid pressure that occur when the oval window vibrates
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Inner ear The inner ear contains structure called the bony labyrinth, which is filled with a fluid called endolymph. The bony labyrinth consists of two parts: The semicircular canals contain the vestibular organs which sense head motion and position The cochlea contains the hearing organ that senses sound vibrations
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Hair cells Hair cells are the primary sensory neurons of the inner ear (for both hearing and vestibular sensation) Hair cells are mechanoreceptors with hair-like protrusions called stereocilia that transduce mechanical movements into nerve signals The stereocilia on each hair cell are graded in height; the tallest one is called the kinocilium On each hair cell, the tips of different stereocilia are joined to one another by tiny protein strands called tip links Tip links are anchored to mechanically gated potassium (K+) channels When the stereocilia are bent toward the kinocilium, mechanically gated K+ channels open; when stereocilia are bent away from the kinocilium, the K+ channels close Opening the K+ channels produces a graded receptor potential that DEPOLARIZES the hair cell! Why? Because the concentration gradient
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