The neck is a structure that stretches from the base of the skull and the inferior margin of the mandible above, to the shoulders and thorax below. It is formed of four major compartments: the vertebral compartment, that includes the cervical vertebrae and the associated postural muscles; the visceral compartment, that contains glands like the thyroid, parathyroid, and thymus, as well as parts of both the respiratory and digestive tracts (larynx, pharynx, trachea, and esophagus); and the two vascular compartments on each side that contain major blood vessels and the vagus nerve. The neck is a known region for vulnerability due to the presence of several of these vital structures.
The bony framework of the neck is comprised of the seven cervical vertebrae, hyoid bone, manubrium of the sternum, and the clavicles. The vertebrae form a pathway for the vertebral artery and veins to pass from the base of the neck to the cranial cavity. They also provide flexibility and a site of attachment for muscles. The hyoid bone is a small U-shaped bone that’s independent from any direct skeletal articulations in the head and neck regions. It anchors several muscles and soft tissue structures in the head and neck, and is highly mobile. The manubrium is the broad superior portion of the sternum. It has a large oval-shaped fossa on each side that articulates with the medial half of the clavicle, which has a sternal end that is triangular and enlarged. The clavicle connects the trunk region with the upper limb.
Muscles of the neck can be grouped based on function, innervation, and embryological origin. Pharyngeal muscles constrict and elevate the pharynx, while the muscles of the larynx adjust the dimensions of the air pathway. The strap muscles are responsible for positioning both the larynx and hyoid bone in the neck, while the postural muscles position the neck and head. Head and upper limb movement are aided by muscles of the outer cervical collar. They are partially formed by the trapezius and sternocleidomastoid muscles, which divide the neck into anterior and posterior triangles on each side. The anterior triangle gives access to the major structures that pass between the head and thorax. While the posterior triangle partially overlies the axillary inlet, and is associated with nerves and vessels passing in and out of the upper limb.
The neck is a relatively slender structure. This permits the flexibility necessary to position the head and provides maximum efficiency for its sensory organs (eyes, ears, mouth, and nose). It also contains important specialized structures like the pharynx and the larynx, which join the upper parts of the digestive and respiratory tracts (consisting of nasal and oral cavities) in the head, with the trachea and esophagus present at the relatively lower aspects of the neck.
The neck’s main vascular supply is comprised of both the left and right common carotid arteries, and the external and internal jugular veins. Its innervation is mainly provided by the cervical plexus and the bilateral phrenic nerve.