Question

Explain the machanism of hearing class 11​

Answer 1

Machanism of Hearing

$\bigstar$ The external ear receives sound waves and directs them to the ear drum. The ear drum vibrates in response to the sound waves and these vibrations are transmitted through the ear ossicles (malleus, incus and stapes) to the oval window.

$\bigstar$ The vibrations are passed through the oval window on to the fluid of the cochlea where they generate waves in the lymphs.

$\bigstar$ The waves in the lymphs induce a ripple in the basilar membrane. These movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane.

$\bigstar$ As a result, nerve impulse are generated in the associated afferent neurons.

$\bigstar$ These impulses are transmitted by the afferent, fibres via auditory nerves to the auditory cortex of the brain where the impulses are analysed and the sound is recognised.

Process of hearing and its path of sound waves is as follows:

Sound waves collected by pinna ⟶ external auditory meatus ⟶ tympanum ⟶ tympanic cavity ⟶ ear ossicles (malleus ⟶ incus ⟶ stapes) ⟶ fenestra ovalis ⟶ perilymph of scala vestibuli ⟶ helicotrema ⟶ scala tympani (vibrations cause movement of Reissner's and basilar membranes result in the vibration of endolymph of scala media) ⟶ Sensory hair cells of organ of Corti ⟶ Impulse generated ⟶ Auditory nerve ⟶ Brain (perception and interpretation of sound vibrations) and sound is perceived.

$\bigstar$ Human ear is adapted to perceive sound frequencies from 20 to 20,000cycles/sec.

$\bigstar$ The minimum loudness of sound a man can hear is of about one decibels.

$\bigstar$ Normal loudness of sound in city homes is 40 to 50dB, while Street noise is of about 70 - 80 dB.