[Campbell Biology P.1163] The auditory system distinguishes between different sounds based on... | Practice Question

The auditory system distinguishes between different sounds based on their volume and pitch. Which statement best explains how these two characteristics are encoded by the ear?

  • A: Volume is determined by the frequency of the sound wave, while pitch is determined by the amplitude.
  • B: Volume is encoded by the amplitude of basilar membrane vibration and the frequency of action potentials, while pitch is encoded by the specific region of the basilar membrane that vibrates and the corresponding area in the cerebral cortex.
  • C: Both volume and pitch are exclusively determined by the rate of neurotransmitter release from hair cells.
  • D: The round window's vibration frequency encodes pitch, while its amplitude encodes volume.

Explanation

The text explicitly states that 'Volume loudness is determined by the amplitude, or height, of the sound wave. A large-amplitude wave causes more vigorous vibration of the basilar membrane, greater bending of the hairs on hair cells, and more action potentials in the afferent neurons'. It also states that 'Pitch is determined by a sound wave's frequency' and that 'The cochlea can distinguish pitch because the basilar membrane is not uniform along its length: It is relatively narrow and stiff near the oval window and wider and more flexible at the apex at the base of the cochlea. Each region of the basilar membrane is tuned to a different vibration frequency... each region is connected by axons to a different location in the cerebral cortex'.