Question

Sensory crista of ampulla of mammalian ear is connected with
A) Sense of balance
B) Sense of low hearing
C) Sense of loud hearing
D) Secretion of ear wax

Answer 1

Hint:Sensory crista are groups of sensory hair cells present at the lower end of each semicircular canal. These crista are covered by a mass of gelatinous material called cupula. It has longer sensory hairs.

Complete answer:
1) In External ear: The external auditory meatus is slightly 'S'-shaped tube about 2.5 cm long in man. It conducts sound waves to the middle ear.
 >It is lined with hairy skin and contains specialized sebaceous glands (considered as modified sweat glands) called ceruminous glands.
 >These secrete cerumen (earwax), a sticky material containing lysozyme and immunoglobulins.
 Foreign materials such as dust, insects and microbes, are prevented from reaching the tympanic membrane by wax, hairs and the curvature of the meatus.
>So the option (D) is wrong.

2) In the internal ear: the coiled portion of the labyrinth is called Cochlea . It is the main hearing organ of the inner ear.
 >It can sense low and high sound with the help of “The organ of corti” located in the basilar membrane of cochlea.
 >It is a sensory structure which contains hair cells Dieter cells (Basal cells) and Hensen's cells (supporting cells) also present.
 >The hair cells act as the auditory receptors. The hair cells are present on the internal side of the organ of corti in a row.
>Each hair cell has two ends i.e. the apical end and the basal end. A large number of processes (projected parts) called stereocilia are projected from the apical part of each hair cell.
 >Hence, each hair cell has a number of stereocilia emerging from its apical part.
 >On the other hand, the basal or the lower end of the hair cell is in close contact with the afferent nerve fibres. These afferent nerve fibres take the nerve impulses away from ear to brain.
 >So, the option B and C are incorrect.

3) The semicircular canals are three in number in each inner ear. It contains a structure which acts as the sensory receptor for sensing change in the position of head or body. And that structure is known as “Crista ampulla”.
 >Location: The base of the semicircular canals is swollen or dilated and is called ampulla. Each ampulla has a ridge projecting ,called crista ampullaris. This projected ridge called crista ampullaris has hair cells.
>The apical ends of the hair cells of crista ampullaris act as the receptors for sensing the changes in the posture or position of the body.
>The basal ends of these hair cells are in close contact with the sensory/afferent nerve fibres of the vestibular branch of the auditory nerve.
>So,These cristae maintain the dynamic balance of the body.

Hence the correct answer is option (A) i.e. sense of balance.

Note:In addition to the neural impulses of sound which are sent only by the ears, the neural impulses for equilibrium are not only sent by the ears. The input to the brain for balance also comes from the receptors present in the muscles, tendons, joint, skin and eyes. The cerebellum receives all these inputs and then gives the motor commands.