Page 19 - LN-NEURAL CONTROL & COORDINATION

(located above the cochlea). It is composed of three semicircular canals and

the otolith organ consisting of the saccule and utricle.
(ii) Each semicircular canal lies in a different plane at right angles to each other.
The membranous canals are suspended in the perilymph of the bony canals.
The base of canals is swollen and is called ampulla, which contains a projecting
ridge called crista ampullaris, which has hair cells.
(iii) The saccule and utricle contain a projecting ridge called macula. The crista
and macula are the specific receptors of the vestibular apparatus responsible
for the maintenance of balance of the body and posture.

Mechanisms of Hearing
(i) Sound waves from the environment are received by the external ear and it
directs them to the ear drum.
(ii) The ear drum vibrates due to sound waves and the vibrations are send to
oval window through the ear ossicles (malleus, incus and stapes).
(iii) The vibrations are passed through the oval window on to the fluid of the
cochlea, where they generate waves in the lymph.

(iv) The waves in the lymph induce a ripple in the basilar membrane.
(v) These movements of the basilar membrane bend the hair cells, pressing
them against the tectorial membrane. Due to this, the nerve impulses are
generated in the associated afferent neurons. 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.
Common Diseases
(i) Meniere’s Syndrome It is a hearing loss due to pathological distension of

membranous labyrinth.
(ii) Eustachitis It occurs due to inflammation of Eustachian tube.
(iii) Tympanitis It is due to inflammation of ear drum.
(iv) Otalgia Pain occurs in ear.
(v) Otitis media Acute infection in middle ear.