L18 The auditory system

• Sounds and hearing:

  • Sounds are periodic compressions of air, water or another medium
  • hearing involves constructing a model of the world e.g. what object does the sound correspond to
  • the brain uses sensory input and prior knowledge about sounds to segregate sounds in the environment
• What is the role of the outer ear?

  captures sound and amplifies it by funnelling it into the smaller auditory canal
• What is the role of the middle ear?

  The eardrum collects the vibrations. The eardrum transmits the vibration to the ossicles whose lever action transfers the vibration to the cochlea.
• What is the role of the inner ear?

  The stirrup sends vibrations throughout the cochlea and to the Orfan of Corti (sound-analysing structure).

  • Four rows of hair cells are embedded in the basilar membrane.
  • Vibration bends the hair cells, opening potassium and calcium channels; this depolarizes the cells and sets off signals in the neurons.

  The hair cells synaptically excite the cells of the auditory nerve.
• What is intensity?


  • How much air fluctuation the sound creates.
  • Measured in decibels
  • Perceptual correlate = loudness
  • Neurons fire more frequently as the sound intensity grows
• What is frequency of sound?

  • the number of air compression/ rarefaction cycles per second that the object creates
  • Measured in Hz
  • Perceptual correlate = pitch
  • The place code = different places along the cochlea response to different sound frequencies
• What is Wernicke’s area?

  Understands spoken language, in the temporal lobe
• What is Broca’s area?

  A region in the frontal lobe of the brain responsible for speech production.