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Hair cell function and purpose
The Organ of Corti rests on the basilar membrane in the cochlear duct and contains inner and outer hair cells and the tectorial membrane. The outer hair cells, of which there are approximately 12,000, receive information from the brain and cochlea and mechanically change the basilar membrane properties at specific spots through elongation or shrinking. This action amplifies soft sounds and sharpens the peak of the traveling wave, improving frequency resolution. The approximately 3,000 inner hair cells transmit information to the brain via the eighth cranial nerve. Damage to the outer hair cells results in reduced hearing ability, especially in noise.
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Hair cell function and purpose
- 1. • The Organof 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 Organof 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 HairCells • 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 HairCells • 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 HairCells • The net effect of their mechanical action is to change the mechanical properties of the basilar membrane at specific spots.
- 7. Outer Hair CellsSharpen the Peak! They are the “muscles” of the cochlea They usually get damaged first Apex Base Lows Basilar Membrane Highs
- 8. • Outer HairCells • 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 CellContributions 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 HairCells • 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 haircells • 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 instrumentscannot 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 willdiscuss more next week regarding reduced hair cell function and hearing instrument performance.