The document discusses the anatomy and function of the inner ear, including the cochlea and organ of Corti. It notes that the organ of Corti contains the hair cells and is located in the scala media of the cochlea. It functions to convert vibrations of the basilar membrane into neural signals via the stereocilia on the hair cells. The inner and outer hair cells detect movement and transmit signals to the auditory nerve.

1. “Organ Of
Corti”
Syed Suhail
Ahmad

2. Anatomy of the Ear
 Pinna:
 The external ear that we can see,it collects sound from the environment.
 Tympanic membrane:
 The eardrum which vibrates when stimulated by sound waves.
 Ossicles:
 The bones of the middle ear.They transfer vibrations from mid brain to Cochlea
1. Malleus
2. Incus
3. Stapes
 Cochlea:
 The snail-shaped, fluid-filled, bony structure of the inner ear.It contains the
basilar membrane and the auditory receptor hair cells.
 Oval Window:
 An opening in the bone of the cochlea that reveals a membrane against which
the baseplate of the stapes presses, transmitting sound vibrations into the fluid-
filled cochlea.

3. Copyright © 2004 Allyn and Bacon

4. Spiral Chambers
The cochlea contains three spiral chambers:
 Scala vestibuli:
 Contains the round window.
 Scala media:
 Contains the organ of Corti.
 Scale tympani:
 Contains the oval window.

5. Reissners membrane
Scala Vestibuli
Scala Media
Scala Tympani
Basilar membrane 5

6.  The O rg a n O f Co rti is the receptor organ that generates nerve
impulses in response to vibration of the basilar membrane
 It lies on the surface of the basilar fibers and basilar membrane
•It consists of supporting cells and specialized type of nerve cells called
hair cells,which are of two types:-
1.A single row of Inner Hair Cells numbering about 3500 and measuring
about 12 micrometers in diameter
2.Three or four rows of Outer Hair Cells numbering about 12,000 and
measuring only about 8 micrometers
•Protruding from each hair cell are structures called s te re o c ilia
•The tectorial membrane lies above the stereocilia – shearing motion
between BM and tectorial membrane – causes stereocilia to be displaced

7. • Its function is to convert BM mechanical movement into neural
activity – achieved in the following way :_
• The stereocilia are joined by fine links called ‘tip links’.
• Deflection of the stereocilia leads to the opening of “transduction
channels”.
• Flow of potassium ions into the hair cell occurs due to voltage
difference between the inside and outside of the hair cell.

8. • Causes the release of neurotransmitter and the initiation of action
potentials in the neurons of the audtiory nerve.
• Action potential propagation is in one direction i.e only down the
length of the axon
• Most of the a ffe re nt neurons make contact with the inner hair cells
• Possibly all information about the input sound is conveyed via the
inner hair cells

9. • They have a role in achieving high sensitivity and sharp tuning
• Most of the e ffe re nt neurons synapse directly with the outer hair cells
• Effe re nt neurons carry information from higher auditory system to
cochlea
• A re nt neurons carry information from the cochlea to the higher
ffe
auditory system

10. Copyright © 2004 Allyn and Bacon

11. • Movement of basilar membrane presses the hair cells against the tectorial
membrane
• Deflection or bending of stereocilia in one direction depolarizes the hair
cells,and bending in the opposite direction hyperpolarizes them.
• This in turn excites the auditory nerve fibers synapsing with their bases
• Upward movement of the basilar fibers rocks the reticular lamina upward
and inward toward the modiolus.
• This causes the hairs on the hair cells to shear back and forth against the
tectorial membrane,thus the hair cells are excited whenever the basilar
membrane vibrates

12. • About 90% of the auditory nerve fibers are stimulated by the inner hair
cells rather than the outer hair cells
• It has been proposed that the outer hair cells in some way control the
sensitivity of the inner hair cells at different sound pitches,this
phenomenon is called “Tuning” of the receptor system
• In this phenomenon,a large no of retrograde nerve fibers pass from the
brain stem to the vicinity of the outer hair cells
• Stimulation of these nerve fibers can actually cause shortening of the
outer hair cells and change their degree of stiffness
• These effects suggest a retrograde nervous mechanism for control of the
ear’s sensitivity to different sound pitches,activated through the outer hair
cells

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