Cochlea & its functions

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Cochlea & its functions

  1. 1. ANMOL JILANI
  2. 2.  Cochlea is a system of coiled tubes.  It consists of:  Three tubes: 1-Scala vestibuli. 2-Scala media. 3-Scala tympani.
  3. 3.  Two membranes: 1-Reissners (vestibular membrane). 2-Basilar membrane
  4. 4. o Perilymph:  Present in scala vestibuli and scala tympani.  Almost identical to CSF. o Endolymph:  Present in scala media.
  5. 5.  Contains 20,000 to 30,000 basillar fibers.  These fibers are stiff,elastic,reed-like structures that are fixed at their basal ends in the center of cochlea (modiolus)but not fixed at their distal ends.
  6. 6.  Length:  The lenghth of the basilar fibers increase progressively from the base of cochlea to its apex.  Diameter:decreases from base to apex of cochlea.  Frequency: Base :high frequency. Apex :low frequency.
  7. 7.  If the foot of stapes moves inward.  The round window bulge outward instantaneously because the cochlea is bounded on the sides by bony walls.  Therefore,the initial effect is to cause the basilar membrane at the very base of the cochlea to bulge in the direction of the round window.
  8. 8.  however,the elastic tension that is built up in the basilar fibers as they bend toward the round window initiates a wave that travels along the basilar membrane toward the helicotreama.
  9. 9.  High frquency sound wave.  Medium frequency sound wave.  Very low frequency sound wave.
  10. 10.  Lies on the surface of bassilar membrane.  Contain mechanically sensitive hair cells which are receptive end-organs and generate nerve impulses in response to sound vibrations.
  11. 11. Inner hair cell. Outer hair cell. Depolarization. Hyperpolarization.
  12. 12.  Stereocilia  Direction toward the longer one  Rapid K influx to tips of the stereocilia  Depolarization of cell membrane  Basilar fiber to scala vestibuli ……… depolarization  Endocochlear Potential  Perilymph (Na, K )  EndoLymph(K, Na )  +80mv diff. all the time

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