Hearing

When we hear a sound, our nervous system is detecting sound waves, pressure waves of air molecules. The frequency of the wave is perceived as pitch, while the amplitude is perceived as loudness.

Sound waves are collected by the external ear and amplified as they travel through the ear canal. When they reach the middle ear, they vibrate the tympanic membrane, the eardrum, causing the attached ossicles, a set of small bones, to move.

The ossicles vibrate the oval window of the cochlea, a coiled structure in the inner ear, causing the fluid within it to move.

The movement is detected by hair cells, which transform the stimulus into neural signals. These signals are sent through the auditory nerve to the brainstem, where they travel through a series of neurons up to the thalamus of the brain, and then to the primary auditory cortex.

Along this pathway, information about the sound is maintained, so that once the signal reaches the primary auditory cortex, basic characteristics, such as pitch, can be identified and perceived. From there, sound information is sent to nearby areas of the cerebral cortex for higher level processing, such as Wernicke's area, which is critical for understanding speech.