The Probert Encyclopaedia of Medicine

EAR

The ear is the organ used for hearing. It converts sound into electrical impulses that are fed to the brain. The external ear is composed of the auricle (the pinna), and the auditory canal (the meatus auditorius externus). The Pinna or auricle surrounds the entrance to the auditory canal. It consists of cartilage covered by skin, with small muscles connecting it to the scalp. At the base of the ear is a fleshy lobe. The meatus auditorius is a canal about three centimeters long in the adult, partly bony and partly cartilaginous, leading from the pinna of the ear to the drum. The lining cells secrete the waxy substance found in the canal. In young children the canal is much shorter. The ear drum (tympanic membrane) is a thin oval-shaped membrane, inserted into a groove around the auditory canal. Normally it is white, glistening and somewhat transparent, so that some of the structures of the middle ear are partly visible when viewed through an auroscope. It separates the auditory canal from the middle ear. The Tympanum or middle ear is
a cavity within the temporal bone. It contains several important structures, including three small bones which connect the drum with the internal ear; they are the malleus or hammer, the incus or anvil, and the stapes or stirrup bone. They transmit the vibrations of sound waves to the inner ear. The Eustachian Tube is a channel of communication between the tympanum and the upper part of the pharynx. It admits air from the throat to the tympanum and so maintains an equal pressure on both sides of the drum. The Labyrinth or internal ear is a series of chambers through the petrous bone, comprising the vestibule, a three-cornered cavity within the tympanum; the semicircular canals communicating with the vestibule; and the cochlea, which makes two and a half turns around an axis called the modiolus. The human ear is capable of detecting sounds in the frequency range 20 hz to 20 khz, approximately.
Research Ear