Logan Steele
The sternocleidomastoid (SCM) muscle is a prominent landmark in the neck, allowing us to bend our neck and turn or tilt our head. It is a two-headed neck muscle, which originates at the manubrium of the sternum (sterno-) and the clavicle (-cleido-), and has an insertion at the mastoid process of the temporal bone of the skull (-mastoid). The SCM muscle is one of the largest and most superficial cervical muscles, and is easily visible and palpable. It is thicker and narrower in the middle, and broader and thinner at either end. The SCM muscle is closely related to certain neurovascular structures that pass through the neck on their way to the head or the periphery of the body.
| Characteristics | Values |
|---|---|
| Full Form | Sternocleidomastoid |
| Synonyms | SCM, Sternomastoid |
| Type | Two-headed neck muscle |
| Location | Extends from the mastoid process at the base of the skull to the collarbones and breastbone |
| Function | Allows bending, turning and tilting of the neck and head |
| Structure | Wider and thinner at the ends, narrow and thicker in the middle |
| Borders | Two neck regions known as triangles |
| Nerve | Accessory nerve |
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What You'll Learn
The SCM muscle is a two-headed neck muscle
The sternocleidomastoid (SCM) muscle is a two-headed neck muscle. It is the largest muscle in the front of the neck and is located just below the skin. The SCM muscle starts at the bottom of the neck, wraps around both sides, and ends at the base of the skull. The muscle is wider and thinner where it starts and ends, and it is narrow and thicker in the middle where the two heads, the sternal and clavicular, merge. The SCM muscle gets its name from its location and parts. Sterno refers to the sternum or breastbone, where the sternal head begins. The clavicular head begins at the centre of the collarbones (clavicle) and merges with the sternal head.
The SCM muscle is closely related to certain neurovascular structures that pass through the neck towards the head or the periphery of the body. The muscle also borders two neck regions known as triangles, which contain important nerves, blood vessels, lymph nodes, and glands. The SCM muscle helps you bend your neck and turn and tilt your head. It also helps to stabilise the neck, assists in breathing, and supports the joint that connects the jaw to the skull, allowing you to open and close your mouth.
The SCM muscle can be used as a reference point to locate the triangles for surgery. The muscle is easily visible and palpable, and you can feel your pulse through it. The SCM muscle can be cared for by managing stress and maintaining good posture. Injuries and tension within the SCM can lead to pain and stiffness, which can be treated through stretching, physical therapy, and osteopathic manipulation.
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SCM muscle function and head movement
The sternocleidomastoid (SCM) muscle is a two-headed neck muscle that originates at the manubrium of the sternum (sterno-) and the clavicle (cleido-), with an insertion at the mastoid process of the temporal bone of the skull. It is the largest and most superficial cervical muscle, easily recognisable and palpable. The SCM muscle is involved in how the neck feels and moves, and it acts in concert with the entire muscular group of the cervicofacial region, aiding in various complex physiological movements.
The SCM muscle helps you bend your neck and turn, tilt, and rotate your head. When both sides of the SCM muscle contract, it flexes the neck and extends the head. When one side acts alone, it causes the head to rotate to the opposite side and flexes laterally to the same side (ipsilaterally). The SCM muscle also plays a role in the breathing process, lifting up the breastbone and collarbones and expanding the thoracic cavity.
The SCM muscle is closely related to certain neurovascular structures that pass through the neck on their way to the head or the periphery of the body. It also protects the vertical neurovascular bundle of the neck, branches of the cervical plexus, deep cervical lymph nodes, and soft tissues of the neck from damage.
Examination of the SCM muscle forms part of the examination of the cranial nerves. It can be felt on each side of the neck when a person moves their head to the opposite side. The SCM muscle is also an important landmark in the neck, dividing it into anterior and posterior triangles.
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SCM muscle anatomy and relation to other structures
The sternocleidomastoid (SCM) muscle is a powerful and large neck muscle that allows you to bend your neck and turn or tilt your head. It is a two-headed neck muscle with attachments to the manubrium of the sternum (sterno-), the clavicle (-cleido-), and the mastoid process of the temporal bone of the skull (-mastoid). The SCM muscle is easily visible and palpable, and it can be felt on both the right and left sides of the neck.
The SCM muscle is an important anatomical landmark within the neck region. It divides the neck into anterior and posterior cervical triangles, helping to define the location of structures such as the lymph nodes for the head and neck. The SCM muscle is closely related to certain neurovascular structures that pass through the neck, including the common carotid artery, accessory nerve, and brachial plexus. It also protects these structures, along with the branches of the cervical plexus, deep cervical lymph nodes, and soft tissues of the neck, from damage.
The SCM muscle is innervated by the accessory nerve (cranial nerve XI), which supplies only motor fibres. The cervical plexus supplies sensation, including proprioception, and the cutaneous branches of the cervical plexus emerge from the posterior edge of the SCM to aid in its proprioceptive functions. The SCM muscle has a variable innervation arrangement, with the "classical anastomotic pattern" observed in 50% of cases.
The SCM muscle is composed of parallel rows of muscular fibres, with about 60% being white anaerobic fibres and 40% being red aerobic fibres. White fibres are generally more powerful and can make stronger contractions, but they fatigue more quickly than red fibres. With age, the relative proportion of red fibres increases. The SCM muscle can be affected by pathological changes, such as muscular torticollis, a tonic spasm of the SCM that can cause difficulties in swallowing, extreme immobility of the throat, facial asymmetries, and scoliosis.
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SCM muscle pulse and visibility
The sternocleidomastoid SCM muscle is a powerful neck muscle that allows you to bend, turn and tilt your head. It is the largest muscle in the front of your neck. The SCM muscle starts at the bottom of your neck, wraps around both sides, and ends at the base of your skull. The SCM muscle borders two neck regions known as triangles. The inner part of the SCM muscle bounds part of the anterior triangle, while the outer part bounds part of the posterior triangle. The SCM muscle is composed of two heads, the sternal head and the clavicular head, which merge to form a thick, rounded muscle.
The SCM muscle is an important anatomical landmark within the neck region. It is easily palpable, and you can feel your pulse through it. The arterial supply of the SCM comes from branches of the external carotid artery, which are palpable with the pulse in the medial-anterior portion of the muscle. Any changes in the SCM muscle can be associated with trigger points, which can cause issues such as ptosis, blurred vision, sinus headaches, and referred pain patterns.
The SCM muscle helps stabilize the neck and maintain posture, even when you are not moving. It also assists in breathing by working with other neck muscles to lift the breastbone and collarbone during inhalation, creating space for the lungs to take in air. Additionally, the SCM muscle supports the temporomandibular joint (TMJ), which connects the jaw to the skull and allows you to open and close your mouth.
Healthcare providers sometimes use the SCM muscle as a reference point to locate important structures within the neck for surgery. The SCM muscle is also associated with SCM syndrome, which can be caused by stress, anxiety, or poor posture. Treatment options for SCM syndrome include stress-relieving techniques, physical therapy, and physiotherapy procedures such as trigger point treatment and neck strengthening exercises.
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SCM muscle variations and surgical importance
The sternocleidomastoid (SCM) muscle is a powerful neck muscle that allows you to bend your neck and turn or tilt your head. It is the largest muscle in the front of your neck and is located just below your skin. SCM has dual innervation and multiple functions. It is a superficially palpable muscle with importance as an anatomical landmark within the neck region.
SCM muscle variations are represented by names such as nutator capitis, mastoideus colli, sternocleidomastoid muscle of Kopfnicker, and sternomastoid muscle. The SCM is unique in terms of variations at its origin. It has a variable innervation arrangement, with the "classical anastomotic pattern" observed in 50% of cases. SCM muscle flaps are used in surgical repair for various conditions, including congenital muscular torticollis, intramuscular hemangioma, pseudosarcomatous proliferative myositis, and pseudotumor of infancy (fibromatosis colli).
The SCM muscle borders two neck regions known as triangles: the anterior triangle and the posterior triangle. These triangles contain important nerves, blood vessels, lymph nodes, and glands. Healthcare providers use the SCM muscle as a reference point to locate these structures for surgery. The SCM acts as an anatomical landmark, protecting the vertical neurovascular bundle of the neck, branches of the cervical plexus, deep cervical lymph nodes, and soft tissues of the neck from damage.
The SCM muscle is also important in maintaining posture and stabilising the neck. It helps lift the breastbone and collarbone during inhalation, creating space for the lungs to take in air. Additionally, it supports the temporomandibular joint (TMJ), which allows the mouth to open and close.
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