The neck connects the skull to the torso, supporting the head and enabling movement. This region houses a dense network of muscles responsible for the head’s range of motion and posture over the spine. These muscles also provide a protective layer for delicate structures, including major blood vessels, nerves, and the upper respiratory and digestive tracts. The musculature is organized into layers, with superficial muscles handling gross motion and deeper groups managing stability and fine control.
Muscles Controlling Major Head Movements
The Sternocleidomastoid (SCM) is a thick, prominent muscle that runs diagonally across the front of the neck. It is named for its attachment points: the sternum and clavicle below, and the mastoid process of the skull above. When one SCM contracts, it rotates the head to the opposite side while tilting it toward the contracting side. When both SCMs contract together, they flex the neck forward, such as when nodding down.
The upper fibers of the Trapezius muscle form a large sheet covering the upper back and the back of the neck. These fibers originate from the base of the skull and neck vertebrae, attaching laterally to the clavicle and shoulder blade. The primary neck action of the upper Trapezius is extension, which is the motion of looking upward. They also work with other muscles to elevate the shoulder blade, such as during shrugging.
Lateral and Deep Neck Stabilizers
The Scalene muscles are a group of three paired muscles—anterior, middle, and posterior—situated deep on the sides of the neck. These muscles are responsible for lateral flexion, tilting the head to the side. They also function as accessory muscles of respiration by helping to elevate the first and second ribs during inhalation. The nerves of the brachial plexus and the subclavian artery pass between the anterior and middle sections, which is relevant in conditions involving nerve compression.
Splenius Muscles
Deeper in the neck are the Splenius muscles (Splenius capitis and Splenius cervicis), which serve as extensors of the head and neck. These muscles work to pull the head backward and assist in rotation and side bending. They are positioned beneath the Trapezius and are responsible for maintaining the head’s alignment.
Suboccipital Muscles
The Suboccipital muscles are a small group located at the base of the skull, just below the occipital bone. They are responsible for the smallest, most precise movements between the skull and the first two cervical vertebrae. These deep muscles fine-tune head position, playing a role in balance and visual tracking.
Anterior Neck and Throat Muscles
The Suprahyoid and Infrahyoid muscles are often referred to collectively as the “strap muscles” due to their thin, ribbon-like appearance. The four Suprahyoid muscles lie above the hyoid bone, a U-shaped bone in the neck that does not articulate with any other bone. Their contraction elevates the hyoid bone and the floor of the mouth, which initiates the swallowing process.
Infrahyoid Muscles
The four Infrahyoid muscles are positioned below the hyoid bone and work to depress the hyoid and the larynx (voice box). This downward action is important for swallowing and is involved in modulating vocal pitch during speech.
Platysma
The Platysma is a broad, thin sheet of muscle that lies just beneath the skin of the neck, extending from the chest up to the lower jaw. Although located in the neck, its main function is to manipulate the skin of the face and neck, contributing to expressions like frowning and assisting in lowering the jaw.