Hair cell
Anatomy and Structure
Hair cells are specialized sensory receptor cells that play a critical role in the sense of hearing and balance in mammals. They are found in the sensory epithelium of the cochlea in the inner ear and in the vestibular system which is responsible for maintaining body balance. Hair cells are named for the bundle of stereocilia on their apical surfaces which resemble hairs under a microscope. These cells are mechanoreceptors that convert mechanical stimuli into electrical signals.
Types of Hair Cells
There are two types of hair cells: inner hair cells (IHCs) and outer hair cells (OHCs). The IHCs are primarily responsible for transmitting sound information to the brain. They are fewer in number and arranged in a single row in the cochlea. The OHCs, on the other hand, are more numerous and arranged in three rows. They play a role in amplifying low-level sounds that enter the cochlea.
Mechanism of Action
The mechanism of action of hair cells involves the deflection of the stereocilia bundle due to the movement of fluid within the cochlea or the vestibular system. This deflection opens mechanically gated ion channels that leads to an influx of positively charged ions into the hair cell. This results in a depolarization of the cell, leading to the release of neurotransmitters at the basal end of the cell. These neurotransmitters then bind to receptors on the afferent nerve fibers, generating an action potential that is transmitted to the brain.
Damage and Regeneration
Unlike other cells in the body, hair cells do not regenerate. Once they are damaged or destroyed, they cannot be replaced. This is the primary cause of sensorineural hearing loss, which is the most common type of hearing loss. Exposure to loud noise, aging, and certain medications can all lead to hair cell damage. Research is ongoing to find ways to protect and regenerate hair cells to restore hearing and balance function.
Clinical Significance
The health and function of hair cells are critical for our sense of hearing and balance. Damage to these cells can lead to hearing loss, tinnitus, and balance disorders. Various strategies are being explored to protect and regenerate hair cells, including gene therapy, stem cell therapy, and the use of certain drugs.