<P> There are two different types of fluid that surround the hair cells of the inner ear . The endolymph is the fluid that surrounds the apical surfaces of hair cells . Potassium is the major cation in the endolymph and is thought to be responsible for carrying the receptor currents in the cochlea . Perilymph is found surrounding the sides and the bases of the hair cells . Perilymph is low in potassium and high in sodium . The different ionic makeups of the surrounding fluid in addition to the resting potential of the hair cell creates a potential difference across the apical membrane of the hair cell, so potassium enters when transduction channels open . An influx of potassium ions depolarizes the cell and causes the release of a neurotransmitter that can initiate nerve impulses in the sensory neurons that synapse on the base of the hair cell . </P> <P> Stereocilia (along with the entirety of the hair cell) in mammals can be damaged or destroyed by excessive loud noises, disease, and toxins and are not regenerable . Environmental noise induced hearing impairment is probably the most prevalent noise health effect according to the U.S. Environmental Protection Agency . Abnormal structure / organization of a bundle of stereocilia can also cause deafness and in turn create balance problems for an individual . In other vertebrates, if the hair cell is harmed, supporting cells will divide and replace the damaged hair cells . </P> <P> The methionine sulfoxide reductase B3 gene (MsrB3), a protein repair enzyme, has been implicated in large scale stereocilia bundle degeneration, as well as many other factors such as gestational age and tolerance to cold environments in plants . Although the exact process of pathogenesis is unknown, it seems to be related to apoptotic cell death . A study based on splicing morpholinos to down - regulate MsrB3 expression in zebrafish showed shorter, thinner, and more crowded cilia, as well as small, misplaced otoliths . Several stereocilia also underwent apoptosis . Injection with wild - type MsrB3 mRNA rescued auditory deficits, suggesting MsrB3 helps prevent apoptosis . </P> <P> Another gene, DFNB74, has been observed as a gene involved in recessive hearing loss . DFNB74 based hearing loss may be related to mitochondrial dysfunction . DFNB74 and MsrB3 based deafness may be related to one another . Research on these genes is based on families with recessive deafness, and multiple nonrelated families with this deafness have mutations on both DFNB74 and MsrB3 . </P>

When the tip links in the cilia stretch ion channels open and