Bass Gear Issue 7 : Page 101Now, here is where things get interesting and mysterious. A structure on a membrane within the cochlea contains thousands of hair cells. Movement of the hair cells generates the neural impulses. Inner hairs located along the inside curve respond to vibration differently from the outer hairs along the outside curve. The inner hairs are arranged in a single row along the lower membrane. The outer hairs are arranged in three rows. Despite having approximately four times more outer hairs than inner hairs, approximately 90 percent of the vibrations of the auditory nerve connect to the inner hair cells. When the fibers vibrate at a resonant frequency, a burst of energy is released in that area, which pushes on corresponding hair cells at that area. When each hair cell is distorted, it fires a pulse. However, a hair cell needs to reset before it can fire another pulse. No matter how hard the burst of energy, the hair cell cannot fire again until it resets. Fig. A Fig. B It is believed that the fastest rate that a pulse can be sent by a nerve is about 1kHz. Accordingly, the hair cells transmit a pulse at up to 1kHz. Huh? So how do we hear frequencies above 1kHz? Well, that part is still a mystery. However, one theory is that the hairs encode vibration information above and below 1kHz by controlling the number of cycles per firing. That is, each hair fires a maximum of once per cycle of vibration/burst of energy. However, the hair may skip vibrations Fig. C %&& !$%# f;c;f; Publication List Using a screen reader? Click Here |
