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In the semicircular canals, the hair cells are found in the crista ampullaris, and the stereocilia protrude into the ampullary cupula. Here, the stereocilia are all oriented in the same direction. In the otoliths, the hair cells are topped by small, calcium carbonate crystals called otoconia. Unlike the semicircular ducts, the kinocilia of hair ...
Outer hair cells extend the hearing range to about 200 kHz in some marine mammals. [16] They have also improved frequency selectivity (frequency discrimination), which is of particular benefit for humans, because it enabled sophisticated speech and music. Outer hair cells are functional even after cellular stores of ATP are depleted. [13]
Hair cells die of old age, acoustic overstimulation and other traumas. [2] Oxotoxin exposure, such as aminoglycoside antibiotics and cisplatin, is also a major contributor to hair cell death. [7] Because mammals have very limited hair cell regeneration, hearing loss is essentially irreversible and therefore a therapeutic target for regeneration.
Once outer hair cells are damaged, they do not regenerate, and the result is a loss of sensitivity and an abnormally large growth of loudness (known as recruitment) in the part of the spectrum that the damaged cells serve. [13] While hearing loss has always been considered irreversible in mammals, fish and birds routinely repair such damage.
Type II neurons on the other hand innervate outer hair cells. However, there is significantly greater convergence of this type of neuron towards the apex end in comparison with the basal end. A 1:30-60 ratio of innervation is seen between Type II neurons and outer hair cells which in turn make these neurons ideal for electromechanical feedback. [9]
The hair cells are the primary auditory receptor cells and they are also known as auditory sensory cells, acoustic hair cells, auditory cells or cells of Corti. The organ of Corti is lined with a single row of inner hair cells and three rows of outer hair cells. The hair cells have a hair bundle at the apical surface of the cell.
Generally, many people lose hearing in their old age, especially high frequency hearing. This is caused by hair cell death, so it is hoped that techniques can be developed, such as by using stem cells or other genetic manipulations, to encourage the inner ear to regenerate its hair cells and restore hearing.
[5] [6] Furthermore, Hensen's cells are also able to regenerate the damaged hair cells in some vertebrates; they undergo phagocytosis to eject the dead or injured hair cells, and reproduce both new hair cells and supporting cells into the cell cycle. One of the reasons is that the supporting cells are differentiated by the embryonic hair cells ...