The organ of Corti is the receptor organ for hearing. It is made up of various supporting cells and hair cells. These include inner hair cells, outer hair cells and border cells. Here, let us discuss the stereocilia hair cells of the inner ear.
Stereocilia in Ear
The flask-shaped inner hair cells of the organ of Corti are larger than the outside hair cells. Inner hair cells only occupy the upper portion of the epithelial layer and are organised in a single row. Each cell’s rounded base rests on the inner phalangeal cells, which are the neighbouring supporting cells. The surface of the inner hair cell has a cuticular plate and a number of short, stiff hairs known as stereocilia.
In the organ of Corti, stereocilia of hair cells are embedded in the tectorial membrane. The stereocilia, which resemble hair-like projections, are grouped in bundles of 30 to 300. They are frequently arranged within the bundles in ascending rows of increasing height, resembling a staircase. Rigid cross-linked actin filaments are in the centre of these hair-like stereocilia. The tips of the stereocilia in adjacent rows in the bundles are connected by filamentous structures known as tip links.
Tip links allow ions to pass through the cell membrane and into the hair cells. When they are stretched, they open the cation-selective channels. Additionally, they help maintain the structure of the hair bundle and transmit force across the bundle.
Mechanism of Hearing
When a moving sound wave induces vibration of the basilar membrane at the resonance point, the basilar fibre, Corti rods, hair cells and lamina reticularis move as a single unit. It triggers stereocilia motions, which activate hair cells and create receptor potential.
These stereocilia are grouped according to their height in ascending order. The shorter stereocilia move along with the displacement of the tall stereocilia embedded in the tectorial membrane.
Potassium enters the system as a result of the stereocilia’s motions and thus opens the mechanotransduction channels located at their tips. The voltage-gated calcium ion channel also opens as a result of potassium influx, allowing calcium to enter the cells. This cell depolarisation triggers the release of glutamate (neurotransmitter) from the hair cells into the acoustic nerves, stimulating the cochlear nerves in the process. The signal of the sound wave is then carried to the brain. The conversion of sound inputs into electrical impulses that are delivered to the brain depends on these ion regulation processes.
Mammals’ stereocilia are not regenerative and are susceptible to damage or destruction from noxious substances, sickness, and excessively loud noises.
This was a brief note on the stereocilia of the inner ear. Stay tuned to BYJU’S NEET to learn more about such exciting topics.
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