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How does bending stereocilia stimulate cochlear hair cells?
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sound reception
Auditory mechanisms in insects. (Left) A scolophore organ. (Top right) The mosquito ear. (Centre right) The ear of the cicada Magicicada septendecim. (Bottom right) The ear of the grasshopper.
Cochlear hair cells are stimulated through the mechanical displacement of stereocilia, which are sensory hairs located at the top of the cell. When sound vibrations cause the basilar membrane to move, shearing forces between the reticular lamina and the tectorial membrane bend the stereocilia.1
The stimulation process functions as follows:
- Depolarization: When stereocilia are bent in the direction of increasing length, ion channels in the cell membrane open. This allows potassium ions to flow into the cell, depolarizing it.1
- Neurotransmitter Release: This depolarization triggers the release of neurotransmitters from the base of the hair cell, which are then absorbed by nearby nerve fibres to send electrical signals along the cochlear nerve.1
- Inhibition: Conversely, when stereocilia are deflected in the opposite direction, the ion channels close, leading to hyperpolarization and inhibition of the cell.1
This mechanism relies on the steep electrical gradient maintained between the endolymph and perilymph, which sensitizes the hair cells to even the slightest sound.1