Question

Following is a list of the events (in a random order) that lead to the formation of an auditory impulse.
(i) Vibration is transferred from the malleus to the incus to the stapes.
(ii) Basilar membrane moves up and down.
(iii) Nerve impulse is transmitted in cochlear nerve to auditory cortex of brain for impulse analysis and recognitions.
(iv) Sound waves pass through ear canal.
(v) Stereocilia of hair cells of organ of Corti rub against tectorial membrane.
(vi) Sound waves cause ear drum to vibrate.
(vii) Nerve impulse is generated.
(viii) Vibrations move from fluid of vestibular canal to the fluid of tympanic canal.
(viii) Vibrations move from fluid of vestibular canal to the fluid of tympanic canal.
(ix) Membrane at oval window vibrates.
Which of the following options represents these events in a correct order?

• A. (iv), (vi), (i), (ix), (viii), (ii), (v), (vii), (iii)
• B. (i), (ii), (iii), (iv), (v), (vi), (vii), (viii), (ix)
• C. (ix), (viii), (vii), (vi), (v), (iv), (iii), (ii), (i)
• D. (iv), (vi), (i), (viii), (ix), (ii), (v), (vii), (iii)

Answer 1

The correct option is A (iv), (vi), (i), (ix), (viii), (ii), (v), (vii), (iii)

The ear not only detects sound but also notes its direction, judges its loudness and determines is pitch.Auditory impulse form through different steps:

1. Sound waves are collected by the pinna and directed inward through external auditory canal.

2. Here they strike the tympanic membrane. The latter begins to vibrate at the same frequency as that of the sound waves.

3. From tympanic membrane, the vibration transmitted across the tympanic cavity by the ear ossicles.The outer ossicles called malleus, inner called stapes, middle ossicles called incus.

4. Stapes is fit into oval window which vibrates. The ear ossicles transmit the vibrations from tympanic membrane to the internal ear and also amplifythem 20 times.

5. Increase in force is important because the sound waves are transmitted from air to a fluid medium.

6. From here, the vibrations are transferred to the basilar membrane and the perilymph in the scala tympani, and are finally dissipated into the air of the middle ear as vibrations of the round window membrane.

7. Vibrations of the floor make the "sensory hair" of receptor cells in the organ of corti move in the overlying gelatinous membrane, and get distorted.

8. This stimulation causes depolarisation of the receptor cells and initiation of receptor( action) potential in the fibres of the auditory nerve.

9. The latter carries the impulses to the cerebral cortex, which interprets the impulses as sound.

So, the correct answer is '(iv), (vi),(i), (ix), (viii), (ii), (v), (vii), (iii)'.