Definition for Organ of Corti
From Biology Forums Dictionary
The organ of Corti lies within the middle chamber of the cochlea. It contains thousands of hair cells, which are the actual vibration receptors. The apical surface of the hair cells contains an array of stereocilia, which give the hair cells their name. Stereocilia are not built from the "9+2" arrangement of microtubules that are found in true cilia.
The hair cells are located between the basilar and tectorial membranes. Vibrations of the endolymph cause vibrations of the basilar membrane. This moves stereocilia at the tips of the hair cells against the tectorial membrane and open potassium channels in them. The influx of K+ from the endolymph depolarizes the cell.
You should note that hair cells differ from most "excitable cells" (neurons and muscle fibers) in their use of potassium ions, not sodium ions, to depolarize the cell.
Depolarization of the hair cell causes the release of a neurotransmitter (probably glutamate) at its basal surface and the initiation of nerve impulses in a sensory neuron that synapses with it. These impulses travel back along the auditory nerve (the 8th cranial nerve) to the brain.
Many people, especially when young, can hear sounds with frequencies (pitches) from as low as 16 to as high as 20,000 hertz (cycles per second). Detection of a given frequency is a function of the location of the hair cells along the organ of Corti with the highest frequencies detected near the base of the cochlea, and the remainder of the sound spectrum detected in a progressive fashion with the lowest frequencies detected by hair cells near the tip.
