Myringoplasty

Myringostomy

Myringotomy

Outer (External) Ear

Sound waves are initially gathered by the flesh-covered elastic cartilage of the outer ear called the pinna, or auricle (Fig. 14-2). The auricular cartilage is folded into several distinct structures with separate names. The helix is the upper outer rim of the auricle, whereas the antihelix is the inner curve that is parallel to the helix. The antihelix has two “legs,” or crura (sing. crus), that divide to form a shallow depression between them, referred to as the triangular fossa. The tragus is the fleshy tag of tissue with a tuft of hair on its underside that covers the opening of the external auditory canal. The antitragus is the small raised prominence that is opposite to the tragus. It is important to remember that elastic cartilage is covered by a layer of connective tissue called perichondrium. When this is separated from the cartilage by trauma, deformities of the pinna may occur. The lobule, usually referred to as the earlobe, is the only noncartilaginous part of the external ear. This fleshy protuberance is composed of adipose tissue.

The gathered sound is then funneled into the external auditory canal. The opening of the auditory canal is termed the auditory (acoustic) meatus. Earwax, or cerumen, is secreted by modified sweat glands within the external auditory canal and protects the ear with its antiseptic property and its stickiness, trapping foreign debris and moving it out of the ear.

The tympanic membrane (TM), or eardrum, marks the end of the external ear and the beginning of the middle ear (Fig. 14-3). This concave membrane of the eardrum is attached to an almost complete ring of bone called the tympanic annulus. The membrane is composed of a thick, taut part (the pars tensa) and a thin, flexible part (the pars flaccida). The center of the membrane is pulled inward, forming a shallow depression termed the umbo. Because the membrane is extremely delicate and vulnerable to perforation and infection, the additional terms naming structures of the eardrum are necessary to specify where the injury occurs.

Middle Ear

The eardrum conducts sound to the air-filled tympanic cavity of the middle ear. The eustachian tube, also called the auditory tube or the pharyngotympanic tube, is a mucous membrane–lined connection between the middle ear and the throat. It functions to supply air for sound conduction and pressure equalization.

The three tiny bones in the middle ear are called the ossicles, or the ossicular chain, and are named for their shapes: the malleus, or hammer; the incus or anvil; and the stapes (pl. stapedes), or stirrup. The ossicles transmit the sound to the oval window through the stapes. The main cavity of the middle ear, opposite the tympanic membrane, is termed the tympanic cavity proper. Above the level of the eardrum is a separate space called the epitympanic recess, or attic.

Inner Ear

Once sound is conducted to the oval window, it is transmitted to a structure called the labyrinth, or the inner ear. A membranous labyrinth is enclosed within a bony labyrinth. Between the two, and surrounding the inner labyrinth, is a fluid called perilymph. Within the membranous labyrinth is a fluid called endolymph. Hair cells within the inner ear fluids act as nerve endings that function as sensory receptors for hearing and equilibrium. Tiny calcium carbonate crystals called otoliths are attached to these hair cells and act as receptors to aid in balance. The outer, bony labyrinth is composed of three parts: the vestibule, the semicircular canals, and the cochlea. The vestibule and semicircular canals provide information about the body’s sense of equilibrium, whereas the cochlea is an organ of hearing. Within the vestibule, two structures called the utricle and the saccule function to determine the body’s static (nonmoving) equilibrium (Fig. 14-1, inset). A specialized patch of epithelium, called the macula, found in both the utricle and the saccule, provides information about the position of the head and a sense of acceleration and deceleration. The semicircular canals detect dynamic equilibrium or a sense of sudden rotation through the function of a structure called the crista ampullaris.

The cochlea receives the vibrations from the perilymph and transmits them to the cochlear duct, which is filled with endolymph. The transmission of sound continues through the endolymph to the organ of Corti, where the hearing receptor cells (hairs) stimulate a branch of the eighth cranial nerve, the vestibulocochlear nerve, to transmit the information to the temporal lobe of the brain.