Anatomy of the Ear
Hearing is one of the five senses. It is a complex process of picking up sound and attaching meaning to it. The human ear is fully developed at birth and responds to sounds that are very faint as well as sounds that are very loud. Even in utero, babies respond to sound. The ability to hear is critical to the attachment of meaning to the world around us.
The outer ear consists of the external portion and the ear canal. The external portion that is seen on each side the head is made of cartilage and soft tissue so that it maintains a particular shape but is also pliable. It serves as a collector of sound vibrations around us and directs the vibrations into the ear canal. It assists in determining the direction and source of sound.
The ear canal is about an inch long and ¼ inch in diameter. It extends from the external portion to the eardrum. The outer portion of the ear canal is cartilage covered with skin that contains hairs and glands that secrete wax. The hairs and wax help to prevent foreign bodies, such as insects or dust, from entering the ear canal. Near the eardrum, the wall of the ear canal becomes bony and covered tightly by skin.
The middle ear begins with the eardrum at the end of the ear canal. The middle ear contains three tiny bones. These three bones form a connection from the eardrum to the inner ear. As sound waves hit the eardrum, it moves back and forth causing these bones to move, forming sound waves or vibrations.
A tube called the eustachian tube runs from the front wall of the middle ear down to the back of the nose and throat. This tube provides ventilation and access to outside air and equalizes air pressure on both sides of the eardrum. We are aware of the eustachian tube at work when we feel air pressure changing in our ears as we yawn, chew, or swallow.
The way the facial and skull bones are structured in children, the eustachian tube is in a relatively flat position. This flat position creates a risk for infection moving from the back of the nose and throat into the middle ear, which frequently causes numerous ear infections during a young child’s life. As the baby grows, the eustachian tube will move into a more tilted position decreasing the risk of repeated ear infections.
The inner ear contains the sensory organs for hearing and balance. The cochlea is the hearing part of the inner ear. Three other parts form the balance portion.
The cochlea is a bony structure shaped like a snail and filled with fluid. Inside the cochlea holds the nerve endings for hearing, called the hair cells.
The vibrations from movement of the middle ear in the cochlea moves the fluid, which stimulates the tiny hair cells. Each hair cells respond to different sound pitches called frequencies.
Signals from these hair cells are translated into nerve impulses. The nerve impulses are sent to the brain by the cochlear portion of the acoustic nerve.