Inner hair cells

Inner hair cells (IHCs) are one of the two types of sensory cells in the mammalian cochlea, the other being the outer hair cells. They are primarily responsible for transducing the mechanical vibrations of sound waves into electrical signals that can be interpreted by the brain.

Structure

Inner hair cells are flask-shaped cells that sit on the basilar membrane in the cochlea of the inner ear. They are surrounded by supporting cells and are in close proximity to the tectorial membrane. The top of each inner hair cell is covered in stereocilia, which are small hair-like projections that respond to the movement of fluid within the cochlea.

Function

The primary function of inner hair cells is to convert the mechanical energy of sound waves into electrical signals. This process, known as mechanotransduction, involves the movement of the stereocilia, which opens mechanically gated ion channels and leads to an influx of potassium ions. This influx causes the cell to depolarize and release neurotransmitters onto afferent auditory nerve fibers, which then transmit the signal to the brain.

Inner hair cells are responsible for the majority of auditory signal transmission. They are connected to approximately 90-95% of afferent nerve fibers, while outer hair cells, which primarily function to amplify sound, are connected to only about 5-10%.

Clinical significance

Damage to inner hair cells can result in sensorineural hearing loss, which is the most common type of hearing loss. This can be caused by a variety of factors, including aging, exposure to loud noise, certain medications, and genetic conditions. Currently, there is no way to regenerate human inner hair cells once they have been lost, making this type of hearing loss permanent.