The differentiating factor between the inner and the outer hair cells lies in the innervations. While the inner hair cells have dense innervations, the outer hair cells have relatively less dense innervations.
Further, the inner hair cells transform the sound vibrations from the fluid in the cochlea to the electrical signals which are passed through the auditory nerves towards the brain. On the other hand, the outer hair cells intensify sounds that are low-level, mechanically entering into fluids of the cochlea.
Functionally and anatomically, the mammalian cochlear hair cells are of two distinct types – the inner and outer hair cells.
Inner Hair Cells
- In humans, the cochlear hair cells comprise one row of inner hair cells, and then three rows of outer hair cells
- These inner hair cells are the actual sensory receptors. It is from this subpopulation, that 95% of the fibres of the auditory nerves emerge towards the brain
- These hair cells transform the vibrations in the cochlear fluids into electrical signals. Then these are relayed through the auditory brainstem and then to the auditory cortex
Outer Hair Cells
- These cells amplify the low-level sounds mechanically, which are directed towards the cochlea
- This amplification is governed by the movement of the hair bundles
- The terminations on these hair cells – almost all, are from the efferent axons arising from cells in the brain
Key Difference between Inner and Outer Hair Cells
The table below depicts the difference between Inner and Outer Hair Cells.
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These are the receptive cells present in the cochlea involved in converting the sound waves into nerve signals |
These are the cells seen in the cochlea that mechanically amplify the low-level sound by the movement of the hair bundles |
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Innervated by relatively more afferent nerves compared to efferent nerves |
Innervated by relatively more efferent nerves compared to afferent nerves |
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Close to 3500 cells in the human cochlea at birth, fewer in number comparatively |
Close to 12000 cells in the human cochlea at birth, greater in number |
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Organized in a single row |
Organized in three rows |
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At the terminals of the inner hair cells |
At the terminals of the outer hair cells |
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No |
Yes |
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Conversion of sound vibrations into electrical signals from the fluids in the cochlea |
Amplifying mechanically the low-level sounds entering into fluids of the cochlea |
You read some differences between Inner and Outer Hair Cells.
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