Histology of the Human Ear I. External ear (Figure ... - Faculty.rmc.edu

(2) Function
(a) Sound waves in the air enter the outer ear and cause vibrations of the
tympanic membrane (eardrum).
(b) Vibration of the tympanic membrane causes vibrations of the middle ear
ossicles.
(c) Vibration of the stapes causes vibration of the oval window in the surface of
the vestibular canal at the base of the cochlea.
(d) Vibration of the oval window causes vibration (pressure waves) in the fluid
of the vestibular canal and (through its communication with the tympanic
canal at the apex of the cochlea) the tympanic canal.
(e) Where the pressure waves in the outer canals (vestibular and tympanic)
are out of phase, they result in vertical vibration of the organ of Corti.
(f) Vertical movement of the organ of Corti causes the tectorial membrane to
move laterally on the surface of the hair cells. The conversion of vertical
movement into lateral movement is due to the lack of movement of the
attachment of the tectorial membrane and the sensory epithelium with the
osseus spiral lamina.
(g) This system converts both frequency (determines the location along the
organ of Corti at which maximum vibration occurs) and intensity
(determines the extent of the vibrating area) of sound into mechanical
movement of hair cell processes. Further processing of the signal in the
spiral ganglion and in the auditory centers in the brain appear necessary to
produce the ability to discriminate among sounds that is demonstrated by
musicians.
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