The neck muscles are responsible for head movement, head posture, swallowing (pharyngeal) and speaking (laryngeal), and are even integrated with jaw movement. They are supported by the cervical vertebrae, collarbone (also known as the clavicle), and sternum, giving the muscles of the neck multiple roles as back and shoulder muscles. The major blood vessels running through the neck and supporting the transport of oxygen to the muscles are the carotid artery and jugular vein. The muscles of the neck are generally named by their origination and end points.
Internal muscles of the throat
The pharynx is essentially a muscular cavity leading to the esophagus and windpipe. The three layers of pharyngeal muscle aid in swallowing. The external layer consists of the superior, middle, and inferior pharyngeal constrictor muscles. The internal layer consists of the stylopharyngus and salpingopharyngus muscles. The third layer separates the pharynx from the esophagus and consists of the cricopharygnus and the pharyngeal-esophageal segment. The P.E. segment must relax for food to pass into the digestive tract.
Speech and breathing are controlled in the throat by the laryngeal muscles. The intrinsic muscles move the vocal folds and consist of the posterior cricoarytenoid, lateral cricoarytenoid, thyroarytenoid, cricothyroid, and interarytenoid muscles. The extrinsic muscles, called the strap muscles (or sometimes the laryngeal elevators), move the larynx up and down, especially during swallowing, preventing entry of food into the airway.
Anterior neck muscles
The anterior muscles can be felt when rubbing along the throat or under the sides of the jaw. They provide support for the larynx, pharynx, and oral cavity. Maricopa Community College offers an interactive diagram to aid in visualizing the muscles as they are discussed here, as well as this illustration from Britannica.
The digastric muscle has an anterior and posterior belly, one going from the chin to the hyoid bone, the other from the hyoid bone to the mastoid. The hyoid bone is the anchor for the tongue. Thus, the digastric acts on both the mouth and the larynx. The stylohyloid also runs from the hyoid bone, but to the skull, specifically the styloid process. The myelohyloid muscle gives the mouth a floor.
Some of the anterior muscles connect to the shoulders and chest. The sternocleidomastoid connects the clavicle and sternum to the skull, specifically the mastoid region, allowing side to side movement and flexion of the head. The omohyoid attaches the clavicle, scapula (shoulder blade), and first rib to the hyoid bone. Strap muscles also extend between the sternum and larynx (sternothyroid), sternum and hyoid (sternohyoid), larynx and hyoid (thyrohyoid), and hyoid and chin (geniohyoid).
Posterior neck muscles
The muscles in the back of the neck support the head by connecting it to the back and shoulders. These muscles are often manipulated by massage to alleviate back pain. The platysma originates in the fascia of the pectoralis and deltoid muscles and ends in the mandible, tightening the neck fascia. The anterior scalene connects between cervical vertebrae 3 and 6, flexing the neck. Other scalenes (posterior, medial) attach to the cervical vertebrae but act on the ribs during the breathing process. The lognissimus capitus allows flexion of the head by connecting the cervical vertebrae and the back of the head (occipital bone). The splenus capitis connects the cervical spine (specifically C7-T3) to the mastoid process, and the splenus cervicus connects the thoracic spine (T3-T6) to the cervical spine (C1 to C4), overlapping to allow rotation of the head and extension of the neck.
The trapezius muscle is a large muscle extending from the back of the neck to the shoulder and down the back. It acts primarily on the shoulder. Just interior to this muscle on the back of the neck is the levator scapulae, which also acts primarily on the shoulder and spine. These muscles are also used in relation to the rhomboids, which connect to the processes of the cervical vertebrae just below the neck, transitioning into the muscles of the back.