HIS 150 Hair Cell Function and Purpose Objective 1

1. • The Organ of Corti
It rests on top of the basilar
membrane. It sets inside the scala
media (cochlear duct) and contains
the inner and outer hair cells and of
course the tectorial membrane.

2. • The Organ of Corti
• This is where the electrical
“language” is transmitted
between the brain and received
sound stimulation.

3. Outer Hair Cells: The Active
Cochlear Mechanism
Note how
embedded
OHCs actually
pull tectorial
membrane
down

4. • Outer Hair Cells
• There are approximately 12,000
outer hair cells. They have the
appearance of test tubes and
mostly receive efferent information
from the brain.

5. • Outer Hair Cells
• Not only do they react to
information received from the brain
but they also receive “chemical
messages” from inside the cochlea
which tell them to either elongate
or shrink (like pistons).

6. • Outer Hair Cells
• The net effect of their mechanical
action is to change the mechanical
properties of the basilar membrane
at specific spots.

7. Outer Hair Cells Sharpen the Peak!
They are the “muscles” of the cochlea
They usually get damaged first
Apex Base
Lows Basilar Membrane Highs

8. • Outer Hair Cells
• They play a very significant role in
the reception of soft sounds.
• Without outer hair cells, we would
have approximately forty to sixty
decibels of sensorineural hearing
loss.

9. Here’s a “Passive” Traveling Wave
A wave without outer hair cells
Apex Base
Basilar Membrane
Fig 1-4, Venema, T. Compression for Clinicians 2nd edition, Thomson Delmar Learning 2006

10. Outer Hair Cell Contributions to the Traveling
Wave
1. Amplify
2. Sharpen
OHCs
Sharpen
Peak
Traveling
Wave
Basilar
Membrane
Displacement
Basilar
Membrane Envelope of
Traveling Wave
Fig 1-5, Venema, T. Compression for Clinicians 2nd edition, Thomson Delmar Learning 2006

11. • In summary, outer hair cells have a
twofold purpose:
1. They amplify soft sounds (below
forty to sixty decibels).
2. They “fine-tune” the frequency
resolution of the basilar
membrane.

12. • Inner Hair Cells
• There are approximately 3,000
inner hair cells which have a pear
or flask shape. They mostly send
afferent information to the brain via
the eighth cranial nerve.

13. • Inner hair cells
• More specifically, the 3,000 hair
cells stimulate approximately
30,000 eighth cranial nerve fibers.
This occurs from each cochlea.

14. Inner hair cells
Outer hair cells
Hair Cells:
A Closer Look
Picture from Australian Hearing
Hear & Now, issue 4, 1998

15. • Hearing instruments cannot
sharpen the peaks of the traveling
wave. They will only increase the
amplitude (size) of the wave.
• With more outer hair cells missing
less resolution may be received by
the brain—especially when noise is
introduced.

16. Normal
Inner
&
Outer
Hair Cells
Fig 1-7, Venema, T.
Compression for
Clinicians 2nd edition,
Thomson Delmar
Learning 2006

17. Damage
d
Hair
Cells
(mostly
outer)
Fig 1-8, Venema, T.
Compression for
Clinicians 2nd edition,
Thomson Delmar
Learning 2006

18. • We will discuss more next week
regarding reduced hair cell
function and hearing
instrument performance.