33.
Explain the mechanism of hearing by the human ear.
The ear pinna collects and directs the sound waves travelling through the air into the external auditory canal.
The sound waves create vibration in the tympanic membrane. These vibrations are transmitted through the chain of ossicles to the perilymph in the vestibule with each tiny inward movement of the membrane the malleus next to it vibrates in the same rhythm, and by a lower action transmits the message to the adjoining incus. The incus in turn, transmits the vibration to stapes. The stapes bone that fits into a membranous opening, the oval window, on the inner wall of the middle ear relays the vibration to the inner ear. Thus in this process the force of vibration undergoes considerable amplification since the chain of ossicles acts as a lever and the area of the tympanic membrane is much greater than that of the foot-plate of stapes which increase the force per unit area. The movement of stapes towards vestibule. Sets up a pressure wave in perilymphs. This wave passes from vestibule into Scala vestibuli and travels through it to the apex of cochlea. At this point Scala vestibuli is continuous with scala tympani. The pressure wave passes into scala tympani and again transverse the whole length of cochlea. In this way vibration are set up in the perilymph and through it in the basilar membrane. The basilar membrane move up and down, distorting Hair cells. These distortions generate nerve impulse that travel through cochlear near to the appropriate part of the brain where the sound perception of the subject is produced.
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