How Do We Hear? – Educational Overview [2018]

The ability to hear is a product of the complexity and sensitivity of the auditory system.

The ear itself is separated into three different parts:

  • The outer ear
  • The middle ear
  • The inner ear

Sound begins as the vibration of air molecules and travels as a wave to the outer ear where it enters the ear canal.

Here, the sound wave vibrates the eardrum, which marks the separation of the outer and middle ear.

Within the middle ear, the three tiniest bones of the human body are suspended within an air filled cavity, the malleus, incus, and stapes.

These bones, called the ossicles, act as a lever system and convert the vibratory energy from the eardrum into mechanical energy.

The final bone in the ossicular chain, the stapes, meets the oval window, a membrane-covered gateway into the cochlea.

Within the cochlea are three fluid-filled channels. Through the movement of the oval window, this fluid is displaced, exciting the sensory organs of hearing, the inner hair cells.

The fluid displacement causes the inner hair cells to fire neural impulses up the auditory portion of the VIIIth cranial nerve, called the vestibulocochlear nerve. 

The VIIIth cranial nerve carries this signal up the brainstem and into the brain, where we recognize sound. At each level of the auditory system, there are complex mechanisms that code for frequency (pitch), intensity (loudness), and time.

Each of these delicate structures are essential to our ability to detect and process sound and speech, almost instantaneously.