3.2.2.2. Hearing

Hearing is a complex process that is used to convert the mechanical movements of a sound wave into action potentials that can be processed by the brain. Sound waves travel from the outer ear to the inner ear, then sound information is sent to the auditory cortex of the brain.

The following lists the steps involved in hearing:

  • 14299-004-D2B5BCF9 hearingThe pinna (earlobe) focuses sound waves so they enter the external ear.
  • Sound pressure wave waves travel into the ear through the auditory canal, also called the external acoustic meatus.
  • The sound wave hits the tympanic membrane (eardrum) at the end of the auditory canal, causing it to vibrate.
  • The auditory ossicles (malleus, incus and stapes) vibrate with the tympanic membrane and amplify the vibrations. The malleus is attached to the tympanic membrane.
  • The last auditory ossicle (stapes) transmits the sound vibrations to the perilymph (fluid) of the inner ear through the oval window. The perilymph fills the scala vestibuli of the spiral-shaped cochlea, which is the hearing part of the inner ear.
  • As the sound travels through the perilymph, it moves the endolymph in the cochlear duct. The endolymph is separate from the perilymph.
  • Movements of the endolymph move the tectorial membrane, which is attached to the sensory hairs of hair cells in the organ of Corti. The hair cells are attached to the basilar membrane, which also moves with the sound vibrations.
  • The sound bends the sensory hairs providing information about the frequency and amplitude of the bending is converted into action potentials
  • The information is sent in the form of action potentials through the vestibulocochlear nerve (cochlear branch) to the auditory cortex of the cerebrum.
  • At the end of the scala vestibuli, any remaining pressure from the sound wave is released through the round (circular) window, so pressure does not build up in the perilymph.
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