The cochlea contains three fluid-filled tubes called scalae that are separated by two membranes. It houses thousands of basilar fibers along the basilar membrane that vary in length, diameter, and stiffness from the base to the apex. When sound waves enter the cochlea, they cause traveling waves along the basilar membrane that peak at different locations depending on the sound frequency. Resting on the basilar membrane are hair cells that detect these waves and transmit neural signals in response to different sound frequencies.

2. ANMOL JILANI

3.  Cochlea is a system of coiled tubes.
 It consists of:
 Three tubes:
1-Scala vestibuli.
2-Scala media.
3-Scala tympani.

4.  Two membranes:
1-Reissners (vestibular
membrane).
2-Basilar membrane

5. o Perilymph:
 Present in scala vestibuli
and scala tympani.
 Almost identical to CSF.
o Endolymph:
 Present in scala media.

6.  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.

7.  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.

8.  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.

9.  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.

10.  High frquency sound wave.
 Medium frequency sound wave.
 Very low frequency sound wave.

11.  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.

12. Inner hair cell.
Outer hair cell.
Depolarization.
Hyperpolarization.

13.  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