Full Ears and Hearing Description
[Continued from above] . . . It leads into the ear canal, which is about one inch long in adults and is closed at the inner end by the eardrum. The eardrum in turn is a thin, fibrous, circular membrane covered with a thin layer of skin. This eardrum separates the outer ear from the middle ear, which is a small cavity that conducts sound to the inner ear by means of three tiny, linked, movable bones called ossicles. These are the smallest bones in the human body and are named for their shape. Lastly, the inner ear is a very delicate series of structures deep within the bones of the skull. It consists of a maze of winding passages, called the labyrinth. The front (see cochlea) is a tube resembling a snail's shell and is concerned with hearing. The rear part is concerned with balance.
The process of hearing involves capturing sound waves and translating them into something the brain can interpret. So as sound enters the ear through the ear canal and strikes the tympanic membrane, vibrations from the tympanic membrane affect the bones in the middle ear that in turn pass the vibration through the oval window into the cochlea. At the bottom of the cochlear duct are the sound-sensitive hair cells. Pressure changes in the cochlear duct transmit bending and shearing movements to these hair cells, stimulating them to produce a nerve signal that is carried to the brain by the cochlear nerve. Additionally, the human body can detect the location of sound by calculating the difference in reception time between both ears, since sound normally reaches one ear a fraction of a second before the other. The source of the source can usually be pinpointed within two to three degrees.