Anatomy and Physiology

The skull is composed of seven bones (two frontal, two parietal, two temporal, and one occipital) that are fused together and covered by the scalp. Bones of the skull are helpful in identifying landmarks on the head ( Fig. 11.1 ). The bony structure of the face is formed from the fused frontal, nasal, zygomatic, ethmoid, lacrimal, sphenoid, and maxillary bones and the movable mandible. The face has cavities for the eyes, nose, and mouth.

Bones of the skull.

Major facial landmarks are the palpebral fissures and the nasolabial folds ( Fig. 11.2 ). Facial muscles are innervated by cranial nerve (CN) V and CN VII. The temporal artery is the major accessible artery of the face, passing just anterior to the ear, over the temporal muscle, and onto the forehead.

Landmarks of the face.

The paired parotid, submandibular, and sublingual salivary glands produce saliva, which moistens the mouth, inhibits formation of dental caries, and starts the digestion of carbohydrates. The parotid glands are located anterior to the ear and above the mandible, the submandibular glands are located medial to the mandible at the angle of the jaw, and the sublingual glands are located anteriorly in the floor of the mouth.

The neck is formed by the cervical vertebrae, ligaments, and the sternocleidomastoid and trapezius muscles, which give it support and movement. The neck begins at the clavicles and sternum inferiorly and at the base of the skull superiorly. It contains the trachea, esophagus, internal and external jugular veins, common carotid, internal and external carotid arteries, and thyroid ( Fig. 11.3 ). Horizontal mobility is greatest between cervical vertebrae 4 and 5 or 5 and 6 in adults. The sternocleidomastoid muscle extends from the upper sternum and medial third of the clavicle to the mastoid process (see Fig. 22.2, C ). The trapezius muscle extends from the scapula, the lateral third of the clavicle, and the vertebrae to the occipital prominence (see Fig. 22.2, C and D ).

Underlying structures of the neck.

A, Anterior view. B, Lateral view.

The relationship of these muscles to each other and to adjacent bones creates triangles used as anatomic landmarks. The anterior triangle is formed by the medial border of the sternocleidomastoid muscles, the mandible, and the midline ( Fig. 11.4 ). The posterior triangle is formed by the trapezius and sternocleidomastoid muscles and the clavicle (see Fig. 11.4 ) and contains the posterior cervical lymph nodes ( Fig. 11.5 ). For a complete description of the lymph nodes of the head and neck, see Fig. 10.8, Fig. 10.9, Fig. 10.10, Fig. 10.11, Fig. 10.12, Fig. 10.13, Fig. 10.14, Fig. 10.15, Fig. 10.16, Fig. 10.17, Fig. 10.18, Fig. 10.19, Fig. 10.20, Fig. 10.21, Fig. 10.22 .

Anterior and posterior triangles of the neck.

Lymphatic drainage system of head and neck.

(If the group of nodes is often referred to by a second name, that name appears in parentheses.)

The hyoid bone, cricoid cartilage, trachea, thyroid, and anterior cervical lymph nodes lie inside these triangles (see Fig. 11.3 ). The common carotid artery and internal jugular vein are deep and run parallel to the sternocleidomastoid muscle along its medial margin. The external jugular vein crosses the surface of the sternocleidomastoid muscle diagonally. The hyoid bone lies just below the mandible. The thyroid cartilage is shaped like a shield, its notch on the upper edge marks the level of bifurcation of the common carotid artery. The cricoid cartilage is the uppermost ring of the tracheal cartilages.

The thyroid is the largest endocrine gland in the body, producing two hormones, thyroxine (T ₄ ) and triiodothyronine (T ₃ ). The two lateral lobes are butterfly shaped and are joined by an isthmus at their lower aspect (see Fig. 11.3 ). This isthmus lies across the trachea below the cricoid cartilage. A pyramidal lobe, extending upward from the isthmus and slightly to the left of midline, is present in about one-third of the population. The lobes curve posteriorly around the cartilages and are in large part covered by the sternocleidomastoid muscles.

Infants

In infants, the seven cranial bones are soft and separated by the sagittal, coronal, and lambdoid sutures ( Fig. 11.6 ). The anterior and posterior fontanels are the membranous spaces formed where four cranial bones meet and intersect. Spaces between the cranial bones permit the expansion of the skull to accommodate brain growth. Ossification of the sutures begins after completion of brain growth, at about 6 years of age, and is finished by adulthood. The fontanels ossify earlier, with the posterior fontanel usually closing by 2 months of age and the anterior fontanel closing by 12 to 15 months of age.

Fontanels and sutures on the infant’s skull.

The process of birth through the vaginal canal often causes molding of the newborn skull, during which the cranial bones may shift and overlap. Within days, the newborn skull usually resumes its appropriate shape and size.

Children and Adolescents

Subtle changes in facial appearance occur throughout childhood. In the male adolescent, the nose and thyroid cartilage enlarge, and facial hair develops, emerging first on the upper lip, then the cheeks, lower lip, and chin.

Pregnant Patients

The fetal thyroid gland becomes functional in the second trimester. Before this time, the pregnant patient is the source of thyroid hormone for the fetus and requires increased iodine intake.

As long as adequate iodine intake is maintained, the size of the thyroid will not detectably change on physical examination; however, a slight enlargement may be detectable on ultrasound ( Fig. 11.7 ).

Thyroid enlargement in pregnancy.

Note the large nodule in the patient’s left lobe. Thyroid size increases in pregnancy in areas of iodine deficiency but not in those with sufficient iodine.

(From Gaw and Murphy, 2013.)

Older Adults

The rate of T ₄ production and degradation gradually decreases with aging, and the thyroid gland becomes more fibrotic.

Review of Related History

For each of the symptoms or conditions discussed in this section, targeted topics to include in the history of the present illness are listed. Responses to questions about these topics provide clues for focusing the physical examination and the development of an appropriate diagnostic evaluation. Questions regarding medication use (prescription and over-the-counter preparations) as well as complementary and alternative therapies are relevant for each.