How Do We Hear Sounds?

People hear sounds when sound waves travel through the air to the ears. The visible outer ear is only a small part of the organ and hearing, and parts of the inner ear transmit the sound waves to the brain.

The external part of the ear is made up of the auricle and the external auditory canal. The auricle has a slightly cupped shape to allow it to collect sound waves and direct them into the auditory canal. The auditory canal then passes sound waves to the middle ear.

The middle ear is separated from the auditory canal by the eardrum, or tympanic membrane. The tympanic cavity contains three tiny, movable bones: the hammer, the anvil and the stirrup. Sound waves pass through the eardrum, across the three bones and into the inner ear.

The inner ear consists of a bony labyrinth and a membranous labyrinth. A fluid known as perilymph separates the two. Sound waves travel through the perilymph to fibers in the basilar membrane in the cochlea. These fibers set up a vibration in the specialized hair cells that make up the organ of Corti, which is the organ of hearing. The vibrations of the hair cells stimulate the nerves attached to them. These nerves in turn send messages through the auditory nerve to the temporal lobe, which is the brain's center of hearing.