External

The external ear consists of two parts: an outer, funnellike structure called the auricle (pinna) and an S-shaped tube, the external auditory (aw'di-to"re) meatus (external auditory canal) that leads inward for about 2.5 centimeters (fig. 12.10).

The external auditory meatus passes into the temporal bone. Near this opening, hairs guard the tube. The opening and tube are lined with skin that contains many modified sweat glands called ceruminous glands, which secrete wax (cerumen). The hairs and wax help keep large foreign objects, such as insects, out of the ear.

Vibrations are transmitted through matter as sound waves. Just as the sounds of some musical instruments are produced by vibrating strings or reeds, the sounds of the human voice are caused by vibrating vocal folds in the larynx. The auricle of the ear helps collect sound waves traveling through air and directs them into the external auditory meatus.

After entering the meatus, the sound waves pass to the end of the tube and alter the pressure on the tympanic membrane (eardrum). The tympanic membrane moves back and forth in response, reproducing the vibrations of the sound wave source.

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