Cochlear dead regions in sensory hearing loss Sensorineural hearing loss

hearing impairment may associated damage hair cells in cochlea. there may complete loss of function of inner hair cells (ihcs) on region of cochlea; called dead region . region can defined in terms of range of characteristic frequencies (cfs) of ihcs and/or neurons adjacent dead region.

cochlear hair cells

figure 3: cross-section of cochlea.

outer hair cells (ohcs) contribute structure of organ of corti, situated between basilar membrane , tectorial membrane within cochlea (see figure 3). tunnel of corti, runs through organ of corti, divides ohcs , inner hair cells (ihcs). ohcs connected reticular laminar , deiters’ cells. there twelve thousand ohcs in each human ear, , these arranged in 5 rows. each ohc has small tufts of hairs , or cilia, on upper surface known stereocilia, , these arranged rows graded in height. there approximately 140 stereocilia on each ohc.

the fundamental role of ohcs , ihcs function sensory receptors. main function of ihcs transmit sound information via afferent neurons. transducing mechanical movements or signals neural activity. when stimulated, stereocilia on ihcs move, causing flow of electric current pass through hair cells. electric current creates action potentials within connected afferent neurons.

ohcs different in contribute active mechanism of cochlea. receiving mechanical signals or vibrations along basilar membrane, , transducing them electrochemical signals. stereocilia found on ohcs in contact tectorial membrane. therefore, when basilar membrane moves due vibrations, stereocilia bend. direction in bend, dictates firing rate of auditory neurons connected ohcs.

the bending of stereocilia towards basal body of ohc causes excitation of hair cell. thus, increase in firing rate of auditory neurons connected hair cell occurs. on other hand, bending of stereocilia away basal body of ohc causes inhibition of hair cell. thus, decrease in firing rate of auditory neurons connected hair cell occurs. ohcs unique in able contract , expand (electromotility). therefore, in response electrical stimulations provided efferent nerve supply, can alter in length, shape , stiffness. these changes influence response of basilar membrane sound. therefore clear ohcs play major role in active processes of cochlea. main function of active mechanism finely tune basilar membrane, , provide high sensitivity quiet sounds. active mechanism dependent on cochlea being in physiological condition. however, cochlea susceptible damage.

hair cell damage

snhl commonly caused damage ohcs , ihcs. there 2 methods might become damaged. firstly, entire hair cell might die. secondly, stereocilia might become distorted or destroyed. damage cochlea can occur in several ways, example viral infection, exposure ototoxic chemicals, , intense noise exposure. damage ohcs results in either less effective active mechanism, or may not function @ all. ohcs contribute providing high sensitivity quiet sounds @ specific range of frequencies (approximately 2–4 khz). thus, damage ohcs results in reduction of sensitivity of basilar membrane weak sounds. amplification these sounds therefore required, in order basilar membrane respond efficiently. ihcs less susceptible damage in comparison ohcs. however, if become damaged, result in overall loss of sensitivity.