NDA (II) 2022 General Ability Test · Question 147 of 150

Correct — B, cochlea. Trace the path a sound takes. The outer ear collects the wave and funnels it down the canal to the eardrum, which vibrates in step with the pressure variations. The three small bones of the middle ear amplify that vibration and pass it to the fluid-filled inner ear. There the cochlea, a coiled spiral chamber, contains sensory hair cells; the fluid waves bend these cells and the bending generates nerve impulses. That is the moment at which mechanical pressure variations become electrical signals, and it happens in the cochlea. The impulses are then carried to the brain by the auditory nerve, where they are interpreted as sound.

• (a)auditory nerve — The auditory nerve carries electrical signals that have already been produced; it transmits rather than converts. It is the wire from the cochlea to the brain, not the transducer.
• (c)eardrum — The eardrum, or tympanic membrane, converts pressure variations in air into mechanical vibration of a membrane. That is a mechanical-to-mechanical step; no electrical signal is created there.
• (d)eustachian tube — The eustachian tube connects the middle ear to the throat and equalises the air pressure on the two sides of the eardrum. It has no role in detecting or converting sound, which is why ears pop rather than hear when it opens.

The human ear has three parts with three distinct jobs. The outer ear collects sound and channels it to the eardrum. The middle ear amplifies the eardrum's vibration through a chain of three tiny bones, the malleus, incus and stapes, and passes it to the inner ear; it also holds the eustachian tube that keeps air pressure balanced across the eardrum. The inner ear contains the cochlea, which turns the mechanical vibration into nerve impulses, and the semicircular canals, which serve balance rather than hearing. The audible range for a healthy young human runs from about twenty hertz to about twenty thousand hertz.

The four options in this item are all real parts of the hearing pathway, so the question is not testing whether you know the names but whether you know the exact stage at which the signal changes form. The useful discipline is to label each stage by what goes in and what comes out — air pressure variations in and membrane vibration out at the eardrum, vibration in and amplified vibration out through the bones, fluid vibration in and nerve impulses out at the cochlea, impulses in and impulses out along the auditory nerve. Only one stage in that chain changes the type of signal. Thinking of the cochlea as the ear's microphone, converting sound into an electrical signal, fixes it firmly.

• The cochlea, in the inner ear, converts pressure variations into electrical nerve impulses.
• The eardrum converts sound waves in air into mechanical vibrations of a membrane.
• The three bones of the middle ear — malleus, incus and stapes — amplify those vibrations.
• The auditory nerve carries the impulses generated in the cochlea to the brain for interpretation.
• The eustachian tube equalises air pressure between the middle ear and the throat and plays no part in hearing itself.

• Choosing the auditory nerve, which carries the electrical signal but does not create it.
• Choosing the eardrum, which does convert something but from air pressure to mechanical vibration only.
• Assuming the eustachian tube is part of the hearing chain because it is part of the middle ear.

As a which-part-does-what item on the hearing pathway, or as a sequence question asking for the order in which the parts act.

No directly related past PYQ was found.

• practice — not a real PYQ

  The three small bones of the middle ear are the malleus, the incus and the

  • (a)cochlea
  • (b)stapes
  • (c)pinna
  • (d)tympanum

  Answer(b) stapes — the three together amplify the eardrum's vibration and pass it to the inner ear.

• practice — not a real PYQ

  The part of the inner ear responsible for the sense of balance rather than hearing is

  • (a)the cochlea
  • (b)the semicircular canals
  • (c)the eardrum
  • (d)the eustachian tube

  Answer(b) the semicircular canals — they sense the position and movement of the head, while the cochlea handles hearing.