Cochlea is a system of coiled tubes.
It consists of:
Present in scala vestibuli
and scala tympani.
Almost identical to CSF.
Present in scala media.
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.
The lenghth of the basilar fibers increase progressively
from the base of cochlea to its apex.
Diameter:decreases from base to apex of cochlea.
Base :high frequency.
Apex :low frequency.
If the foot of stapes moves inward.
The round window bulge outward
instantaneously because the cochlea
is bounded on the sides by bony
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.
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
High frquency sound wave.
Medium frequency sound wave.
Very low frequency sound wave.
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
Direction toward the longer one
Rapid K influx to tips of the stereocilia
Depolarization of cell membrane
Basilar fiber to scala vestibuli ………
Perilymph (Na, K )
EndoLymph(K, Na )
+80mv diff. all the time
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