The neck is the bridge between the head and the rest of the body. It is located in between the mandible and the clavicle, connecting the head directly to the torso, and contains numerous vital structures. It contains some of the most complex and intricate anatomy in the body and is comprised of numerous organs and tissues with essential structure and function for normal physiology. Structures contained within the neck are responsible for breathing, speaking, swallowing, regulation of metabolism, support and connection of the brain and cervical spine, and circulatory and lymphatic inflow and outflow from the head.[1]
Structure and Function
The neck can be envisioned very simply as a pathway (or connection) between the head and the rest of the body. It is home to the proximal esophagus, trachea, thyroid gland, and the parathyroid glands. It provides conduits for blood flow to the brain and head, supports the head and moves it accordingly, and transmits nervous signals from the brain to the rest of the body. It is an intricate part of the body with many different planes and compartments.
The neck separates into two triangles: anterior and posterior, with these divided into additional triangles and anatomic areas. The anterior triangle is surrounded inferiorly by the sternal notch and clavicle, laterally by the sternocleidomastoid, and medially by the trachea, thyroid, and cricoid cartilages.[2] The posterior triangle is bordered posteriorly by the trapezius muscle, anteriorly by the sternocleidomastoid muscle, and inferiorly by the clavicle.[3]
The anterior triangle is subdivided into four smaller segments (also triangles): the submental, submandibular, carotid, and muscular triangles.
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The submental triangle, also called the suprahyoid triangle, contains the mylohyoid muscle as its floor. Inferiorly, its border is the hyoid bone. Medially, its border is the midline of the neck. Posteriorly, the border is the anterior belly of the digastric.[1]
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The submandibular triangle, or the submaxillary triangle, is superiorly bordered by the mandible. The other portions of the triangle are the anterior and posterior bellies of the digastric muscle.[1]
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The carotid triangle, or the superior carotid triangle, is bordered posteriorly by the sternocleidomastoid muscle, anteriorly by the omohyoid muscle, and superiorly by the stylohyoid muscle and posterior belly of the digastric. The thyrohyoid, hyoglossus, middle pharyngeal constrictor, and inferior pharyngeal constrictor muscles form the floor of the carotid triangle.[1]
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The muscular triangle, or the inferior carotid triangle, is bordered medially by the midline of the neck, superiorly by the superior belly of the omohyoid, and posteriorly by the sternocleidomastoid.[1]
The posterior triangle is divided into the occipital triangle and subclavian triangle by the inferior belly of the omohyoid muscle.[1]
The neck also has several layers of fascia, but the two main divisions are superficial and deep fascia.
The superficial cervical fascia extends from the head down to the thorax and axillae. In the neck, it contains the superficial lymph nodes, cutaneous nerves, external and anterior jugular veins, and the platysma muscle. It is arranged loosely to allow for neck movement.[1][4]
The deep cervical fascia subdivides into the superficial layer of deep cervical fascia, the middle layer of deep cervical fascia, and the deep layer of deep cervical fascia.[5]
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The superficial layer of deep cervical fascia, or investing layer, lies between the muscles of the neck and the superficial cervical fascia, encircling the sternocleidomastoid and trapezius muscles. It attaches inferiorly to the scapula, clavicle, and manubrium. Superiorly, it attaches to the mandible, mastoid process, superior nuchal line, and external occipital protuberance.[5]
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The middle layer of deep cervical fascia, or the pretracheal layer, runs from the mediastinum inferiorly to the skull base superiorly. It has a muscular and visceral division. The muscular division encloses the strap muscles, sternohyoid, sternothyroid, omohyoid, and thyrohyoid muscles. The visceral division encloses the larynx, pharynx, esophagus, thyroid, parathyroid glands, trachea, and recurrent laryngeal nerve.[5]
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The deep layer of deep cervical fascia, or prevertebral layer, runs from the skull base to the mediastinum. Its two divisions are the alar and prevertebral layers. These layers surround the deep muscles of the neck and the cervical vertebrae, forming part of the retropharyngeal space.[5]
