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Outer ear (pinna, ear canal, surface of ear drum)
The outer ear is the most external portion of the ear. The outer ear includes the pinnae (also called auricle), the ear canal, and the very most superficial layer of the ear drum (also called the tympanic membrane). In humans, and almost all vertebrates, the only visible portion of the ear is the outer ear. Although the word "ear" may properly refer to the pinna (the flesh covered cartilage appendage on either side of the head), this portion of the ear is not vital for hearing. The complicated design of the human outer ear does help capture sound (and imposes filtering that helps distinguish the direction of the sound source), but the most important functional aspect of the human outer ear is the ear canal itself. Unless the canal is open, hearing will be dampened. Ear wax (medical name - cerumen) is produced by glands in the skin of the outer portion of the ear canal. This outer ear canal skin is applied to cartilage; the thinner skin of the deep canal lies on the bone of the skull. Only the thicker cerumen-producing ear canal skin has hairs. The outer ear ends at the most superficial layer of the tympanic membrane. The tympanic membrane is commonly called the ear drum.
The pinna helps direct sound through the ear canal to the tympanic membrane (eardrum). In some animals with mobile pinnae (like the horse), each pinna can be aimed independently to better receive the sound. For these animals, the pinnae help localize the direction of the sound source. Human beings localize sound within the central nervous system, by comparing arrival-time differences and loudness from each ear, in brain circuits that are connected to both ears.
Human outer ear and culture
Extensive ear modification.
Although the function of the human auricle is rudimentary in terms of hearing, the ears do have an effect on facial appearance. In Western societies, protruding ears (present in about 5% of the Europeans & descendants) have been considered unattractive, particularly if asymmetric. The first surgery to reduce the projection of prominent ears was published in the medical literature in 1881.
The ears have also been ornamented with jewelery for thousands of years, traditionally by piercing of the earlobe. In some cultures, ornaments are placed to stretch and enlarge the earlobes to make them very large. Tearing of the earlobe from the weight of heavy earrings, or from traumatic pull of an earring (for example by snagging on a sweater being removed), is fairly common. The repair of such a tear is usually not difficult.
A cosmetic surgical procedure to reduce the size or change the shape of the ear is called an otoplasty. In the rare cases when no pinna is formed (atresia), or is extremely small (microtia) reconstruction the auricle is possible. Most often, a cartilage graft from another part of the body (generally, rib cartilage) is used to form the matrix of the ear, and skin grafts or rotation flaps are used to provide the covering skin. However, when babies are born without an auricle on one or both sides, or when the auricle is very tiny, the ear canal is ordinarily either small or absent, and the middle ear often has deformities. The initial medical intervention is aimed at assessing the baby's hearing and the condition of the ear canal, as well as the middle and inner ear. Depending on the results of tests, reconstruction of the outer ear is done in stages, with planning for any possible repairs of the rest of the ear.
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