Anatomy and Physiology of the Auditory System

The auditory system consists of several main parts that help carry sounds/signals to the brain. Although hearing seems like a simple feat, the transduction of a signal through the auditory system up to the brain is quite complex.

The Outer Ear

Beginning with the outer portion of the ear, the pinna helps pick up sounds and funnel them into the ear canal, anatomically known as the external auditory canal. The pinna helps individuals localize where sounds are coming from. Sound then travels down the ear canal where it eventually reaches the eardrum, or the tympanic membrane. The tympanic membrane is a thin membrane of skin that vibrates with sound stimulation.

The Middle Ear

Once sound vibrates the tympanic membrane, sound is transferred across three bones (ossicles) in the air filled middle ear space. These ossicles are the tiniest bones in the body known as the malleus, the incus, and the stapes. The stapes bone is shaped like a stirrup and has a round footplate. These three bones work together as a lever system to mechanically transduce sound through the middle ear to the inner ear. As sound reaches the stapes, the footplate pushes on what is referred to as the oval window. This window is the beginning of the inner ear system.

The Inner Ear

After sound reaches the oval window, the stimulation causes fluid in the inner ear system to move. The inner ear is a fluid filled space and therefore sound is hydromechanically transduced. Within the inner ear is an important hearing organ called the cochlea. The cochlea is a snail-shaped organ which has many tiny receptor hair cells embedded in a basilar membrane which respond to certain frequencies of sound. This is known as tonotopic organization in which the base of the membrane in the cochlea responds to higher pitches and the apex responds to lower pitches. As the hair cells are stimulated by the fluid moving in the cochlea, neurons attached to the hair cells receive the signal then send the auditory signal along the auditory nerve and up to the auditory cortex in the temporal lobe of the brain. Although we perceive and interpret sound within milliseconds, the pathway that sound travels to get to the brain is very complex, as detailed above.

There is much more detail related to the process of hearing and understanding, but the above is a basic overview of how individuals hear and interpret a signal. For a more in depth explanation, watch the links below.