Ears, Nose, and Throat

Ears and Hearing

The ear is a sensory organ that identifies, localizes, and interprets sound and helps to maintain balance. It is divided into the external, middle, and inner ear ( Figs. 13.1 and 13.2 ).

The external ear, including the auricle (or pinna) and external auditory canal, is cartilage covered by skin. The auricle, extending slightly outward from the skull, is positioned on a nearly vertical plane. Note its structural landmarks in Fig. 13.3 .

The external auditory canal, an S-shaped pathway leading to the middle ear, is approximately 2.5 cm (1 inch) long in adults. Its skeleton of bone and cartilage is covered with thin, sensitive skin. This canal lining is protected and lubricated with cerumen, a waxy substance secreted by the apocrine glands in the distal third of the canal. Cerumen provides an acidic environment that inhibits the growth of microorganisms.

The middle ear is an air-filled cavity in the temporal bone. It contains the ossicles, three small, connected bones (malleus, incus, and stapes) that transmit sound from the tympanic membrane to the oval window of the inner ear. The air-filled cells of the mastoid area of the temporal bone are continuous with the middle ear. The tympanic membrane, surrounded by a dense fibrous ring (annulus), separates the external ear from the middle ear. It is concave, being pulled in at the center (umbo) by the malleus. The tympanic membrane is translucent, permitting the middle ear cavity and malleus to be visualized. Its conical shape and oblique position to the auditory canal account for the triangular light reflex seen in an otoscopic examination. Most of the tympanic membrane is tense (the pars tensa), but the superior portion (pars flaccida) is more flaccid ( Fig. 13.4 ).

The middle ear mucosa produces a small amount of mucus that is rapidly cleared by the ciliary action of the eustachian tube, a cartilaginous, fibrous, and bony passageway between the nasopharynx and the middle ear. The eustachian tube drains into the posterior aspect of the inferior turbinate of the nose. Muscles briefly open this passage during swallowing, yawning, or sneezing to clear middle ear secretions and equalize the middle ear pressure with atmospheric pressure. The equalized pressure in the middle ear permits the tympanic membrane to vibrate freely with sound waves.

The inner ear is a membranous, curved cavity inside a bony labyrinth consisting of the vestibule, semicircular canals, and cochlea. The cochlea, a coiled structure containing the organ of Corti, transmits sound impulses to the eighth cranial nerve. The semicircular canals contain the end organs for vestibular function. Equilibrium receptors in the semicircular canals and vestibule of the inner ear respond to changes in direction of movement and send signals to the cerebellum to maintain balance.

Hearing is the interpretation of sound waves by the brain. Sound waves travel through the external auditory canal, strike the tympanic membrane, and cause it to vibrate. The malleus, attached to the tympanic membrane, and the serially connected incus and stapes begin vibrat ing. The vibrations are passed from the stapes to the oval window of the inner ear (see Fig. 13.2 ). Oval window movement transmits cochlear endolymph fluid motion to the round window, where it dissipates. Hair cells in the organ of Corti detect sound vibrations and send the information to the auditory division of the eighth cranial nerve. These impulses are transmitted to the temporal lobe of the brain for interpretation. Sound may also be transmitted by bone vibrations of the skull that pass to the inner ear.

Nose, Nasopharynx, and Sinuses

The nose and nasopharynx provide a passage for inspired and expired air, humidify, filter, and warm inspired air, identify odors, and provide resonance for laryngeal sound. The external nose is formed by skin-covered bone and cartilage. The nares (anterior openings of the nose) are surrounded by the cartilaginous alae nasi and columella. The frontal and maxillary bones form the nasal bridge ( Fig. 13.5 ).

The nasal floor is formed by the hard and soft palates, whereas the roof is formed by the frontal and sphenoid bones. A vascular mucous membrane, thickly lined with small hairs and mucous secretions, covers the internal nose. The hairs and mucus collect and carry debris and bacteria from the inspired air to the nasopharynx for swallowing or expectoration. The mucus contains immunoglobulins and enzymes that serve as a defense against infection. Receptors for smell are located in the olfactory epithelium that lines about half of the nasal cavities.

The internal nose is divided by the septum into two anterior cavities: the vestibules. Inspired air enters the nose through the nares and passes through the vestibules to the choanae, posterior openings leading to the nasopharynx. The cribriform plate, housing the sensory endings of the olfactory nerve, lies on the roof of the nose. The Kiesselbach plexus, a convergence of small, fragile arteries and veins, is located on the anterior-inferior portion of the septum. The adenoids lie on the posterior wall of the nasopharynx ( Fig. 13.6 ).

Turbinates—parallel, curved bony structures covered by vascular mucous membrane—form the lateral walls of the nose and protrude into the nasal cavity. They increase the nasal surface area to warm, humidify, and filter inspired air. A meatus below each turbinate is named for the turbinate above it. The inferior meatus drains the nasolacrimal duct, the middle meatus drains the paranasal sinuses, and the superior meatus drains the posterior ethmoid sinus.

The paranasal sinuses are air-filled, paired extensions of the nasal cavities within the bones of the skull. They are lined with mucous membranes and cilia that move secretions along excretory pathways. Their openings into the middle meatus of the nasal cavity are easily obstructed.

Only the maxillary and frontal sinuses are accessible for physical examination. The maxillary sinuses lie along the lateral wall of the nasal cavity in the maxillary bone. The frontal sinuses that develop during childhood are in the frontal bone superior to the nasal cavities. The ethmoid sinuses lie behind the frontal sinuses and near the superior portion of the nasal cavity. The sphenoid sinuses are deep in the skull behind the ethmoid sinuses ( Fig. 13.7 ).

Mouth and Oropharynx

The mouth and oropharynx release air for vocalization and expiration. They also provide passage for food, liquid, and saliva (either swallowed or vomited), initiate digestion through solid food mastication and salivary gland secretion, and identify taste. The oral cavity is divided into the mouth and the vestibule, the space between the buccal mucosa and the outer surface of the teeth and gums. The mouth, housing the tongue, teeth, and gums, is the anterior opening of the oropharynx. The bony arch of the hard palate and the fibrous soft palate form the roof of the mouth. The uvula hangs from the posterior margin of the soft palate ( Fig. 13.8 ).

Loose, mobile tissue covering the mandibular bone forms the floor of the mouth. The tongue is anchored to the back of the oral cavity by its base and to the floor of the mouth by the frenulum. The dorsal surface of the tongue is covered with thick mucous membrane supporting the filiform papillae. Fungiform papillae (taste receptors) are scattered throughout the filiform papillae of the tongue, and specific areas are sensitive to the five basic taste sensations of sour, sweet, salty, bitter, and umami (savory). The ventral surface of the tongue has visible veins and fimbriated folds (fringelike projections of thin mucous membrane) ( Fig. 13.9 ).

The parotid, submandibular, and sublingual salivary glands are located in tissues surrounding the oral cavity. The secreted saliva initiates digestion and moistens the mucosa. Stensen ducts are parotid gland outlets that open on the buccal mucosa opposite the second molar on each side of the upper jaw. Wharton ducts open on each side of the frenulum under the tongue. They drain saliva from the submandibular and sublingual glands to the sublingual caruncle at the base of the tongue. The sublingual glands have many ducts opening along the sublingual fold (see Fig. 13.9 ).

The gingivae, consisting of fibrous tissue covered by mucous membrane, are attached directly to the teeth, maxilla, and mandible. The roots of the teeth are anchored to the alveolar ridges of the maxilla and mandible. The enamel-covered crown is visible for examination. Adults generally have 32 permanent teeth ( Fig. 13.10 ).

The oropharynx, continuous with but inferior to the nasopharynx, is separated from the mouth by bilateral anterior and posterior tonsillar pillars. The tonsils, lying in the cavity between these pillars, have crypts that collect cell debris and food particles.

Swallowing is initiated when food is forced by the tongue toward the pharynx. Muscles in the pharynx contract and prevent movement of the food into the nasopharynx, and respiration is inhibited as the epiglottis closes. Food is then propelled into the esophagus.

History of Present Illness