The Auditory System: Learn It 1—Anatomy of the Ear

  • Describe the anatomy of the auditory system
  • Understand how sound waves shape our hearing
  • Explain how we perceive pitch and localize sound
  • Describe types of hearing loss

The Auditory System: How We Hear

Our auditory system transforms vibrations in the air into the meaningful sounds of speech, music, and the environment. This process allows us to appreciate language, rhythm, and even the quiet rustle of leaves. Let’s explore the anatomy of the ear, how sound becomes a neural signal, how we perceive pitch and locate sound, and what happens when hearing is impaired.

Anatomy of the Auditory System

The ear can be separated into multiple sections: the outer, middle, and inner ear.

outer, middle, and inner ear structures

The outer ear includes the pinna, which is the visible part of the ear that protrudes from our heads, the auditory canal, and the tympanic membrane, or eardrum.

 

The middle ear contains three tiny bones known as the ossicles, which are named the malleus (or hammer), incus (or anvil), and the stapes (or stirrup).

 

The inner ear contains the semicircular canals, which are involved in balance and movement (the vestibular sense), and the cochlea. The cochlea is a fluid-filled, snail-shaped structure that contains the sensory receptor cells (hair cells) of the auditory system (Figure 1).

An illustration shows sound waves entering the “auditory canal” and traveling to the inner ear. The locations of the “pinna,” “tympanic membrane (eardrum)” are labeled, as well as parts of the inner ear: the “ossicles” and its subparts, the “malleus,” “incus,” and “stapes.” A callout leads to a close-up illustration of the inner ear that shows the locations of the “semicircular canals,” “urticle,” “oval window,” “saccule,” “cochlea,” and the “basilar membrane and hair cells.”
Figure 1. The ear is divided into outer (pinna and tympanic membrane), middle (the three ossicles: malleus, incus, and stapes), and inner (cochlea and basilar membrane) divisions.

From Sound Waves to Neural Signals

Here’s how sound becomes perception:

  1. Sound waves travel through the auditory canal and cause the eardrum to vibrate.
  2. The ossicles amplify and transmit those vibrations to the oval window of the cochlea.
  3. The movement of the stapes at the oval window sets the cochlear fluid in motion.
  4. This motion bends the stereocilia (tiny hairlike projections) on the hair cells in the organ of Corti.
  5. Bending of the stereocilia opens ion channels, generating electrical impulses.
  6. These impulses travel along the auditory nerve to the brainstem, then to the thalamus, and finally to the auditory cortex in the temporal lobe.

Like vision, auditory information travels along parallel pathways for different functions:

  • A “what” pathway helps identify the source or type of sound.
  • A “where/how” pathway helps determine the sound’s location and movement in space (Rauschecker & Tian, 2000; Renier et al., 2009).
Watch the process of audition in the following video:

You can view the transcript for “Process of Hearing Animation YouTube” here (opens in new window).