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The sternocleidomastoid (SCM) muscle is a prominent structure in the neck, with important functions and anatomical relationships. It is a two-headed muscle, originating from the sternum and clavicle, and inserting into the mastoid process of the temporal bone. The SCM is a large and superficial muscle, easily visible and palpable, serving as a primary landmark in the neck. It divides the neck into anterior and posterior triangles, aiding in the location of structures like lymph nodes. The SCM has multiple functions, including rotating the head, flexing the neck, and assisting in respiration. It is also associated with various pathologies, such as torticollis and temporomandibular joint disorders. The SCM's complexity and size make it susceptible to injuries and tension, which can be managed through treatments such as physical therapy, osteopathic manipulation, and stress reduction.
| Characteristics | Values |
|---|---|
| Type | Two-headed neck muscle |
| Location | Front and sides of the neck |
| Appearance | Thick and narrow at its center, broader and thinner at either end |
| Functions | Rotation of the head to the opposite side, flexion of the neck, accessory muscle of respiration, stabilizes the neck |
| Innervation | Accessory nerve (Cranial nerve XI) |
| Blood supply | Superior thyroid artery |
| Susceptible to | Strain, injury, sprains, atrophy, tumors |
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What You'll Learn
The sternocleidomastoid muscle is a prominent landmark in the neck
The sternocleidomastoid muscle plays a central role in the formation of the triangles of the neck. It divides the neck into anterior and posterior cervical triangles (in front and behind the muscle, respectively), which helps define the location of structures such as the lymph nodes for the head and neck. The anterior triangle is further divided into the submental, submandibular, carotid, and muscular triangles. The posterior border of the SCM, the inferior border of the mandible, and the medial line of the neck delimit the anterior triangle.
The SCM has multiple functions, including rotation of the head to the opposite side and flexion of the neck. When acting unilaterally, it rotates the neck to the opposite side and flexes laterally to the same side (ipsilaterally). When acting bilaterally, it flexes the neck and extends the head. In addition to these movements, the SCM also serves to stabilize the neck and maintain its healthy alignment with the torso. It is also an accessory muscle of respiration, working with other neck muscles to lift the breastbone and collarbone during inhalation, creating space for the lungs to take in air.
The SCM is susceptible to various conditions, such as injuries, sprains, strains, atrophy, and tumors, which can lead to neck stiffness, pain, and other symptoms. One such condition is sternocleidomastoid syndrome, which can be acute or chronic and is characterized by tightened, sensitive areas, or trigger points within the muscle. Another condition is torticollis (wryneck), where short, tightened SCM muscles cause the head to naturally turn or tilt to one side. This disorder can result in difficulties swallowing, extreme immobility of the throat, facial asymmetries, and scoliosis.
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It is a large, powerful muscle
The sternocleidomastoid muscle is one of the largest and most prominent muscles in the front of the neck. It is a two-headed muscle, with one head originating at the manubrium of the sternum and the other at the clavicle. The two heads join to form a thick, rounded muscle that inserts at the mastoid process of the temporal bone of the skull. This muscle is easily visible and palpable, and it serves as a primary landmark of the neck.
The sternocleidomastoid muscle is a powerful muscle that plays a crucial role in neck movement and stability. It is responsible for flexion of the neck, allowing the neck to bend both laterally and anteriorly. It also enables the rotation of the head to the opposite side of the contracting muscle. This muscle works bilaterally, with both sides contracting simultaneously to flex the neck, and unilaterally, with one side contracting to rotate the head.
The muscle's powerful action is facilitated by its attachment to multiple bones, including the sternum, clavicle, and temporal bone of the skull. Its thick and rounded structure provides the necessary force to perform neck flexion and head rotation. The muscle's broad origin and insertion points also contribute to its strength, allowing for a greater range of motion and stability during movement.
The sternocleidomastoid muscle is closely associated with the neck's neurovascular structures. It helps protect the vertical neurovascular bundle, branches of the cervical plexus, deep cervical lymph nodes, and soft tissues of the neck from damage. The muscle's proximity to these structures highlights its importance in maintaining neck health and stability.
The size and complexity of the sternocleidomastoid muscle make it susceptible to various conditions, such as torticollis or wryneck, which can cause neck stiffness, pain, and trigger points. It is important to maintain good posture and manage stress to prevent injuries and tension in this muscle. Overall, the sternocleidomastoid muscle's large size and powerful functions make it a prominent and essential structure in the neck region.
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The muscle has multiple functions
The sternocleidomastoid muscle has multiple functions. Firstly, it is responsible for rotating the head to the opposite side and flexing the neck. This means that it allows you to bend your neck and turn or tilt your head. When acting together, the muscles on both sides of the neck flex the neck and extend the head. When acting alone, the muscle rotates the head to the opposite side and slightly flexes to the same side.
Secondly, the sternocleidomastoid muscle acts as an accessory muscle of respiration. It is an inspiratory breathing muscle, as it lifts the sternum and clavicle, expanding the thoracic cavity. It also works with other neck muscles to lift the breastbone and collarbone when inhaling, creating space for the lungs to take in air.
Thirdly, the muscle plays a role in maintaining posture and stabilising the neck. It helps to support the temporomandibular joint (TMJ), which is the joint that connects the jaw to the skull and allows the mouth to open and close.
Lastly, the muscle serves as an important anatomical landmark in the neck. It divides the neck into anterior and posterior cervical triangles, which helps to define the location of structures such as the lymph nodes for the head and neck.
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It is susceptible to strain and injury
The sternocleidomastoid (SCM) muscle is the largest neck muscle in the front of your neck. It is a two-headed muscle that runs down the front of your neck and splits to attach to the top of your sternum and collarbone. SCM pain can be caused by muscle tension, performing repeated motions, or certain health conditions such as asthma or pneumonia.
The SCM muscle’s size and complexity make it susceptible to strain and injury. The SCM is a long, thick muscle that is easily visible and palpable. It is thick and narrow at its center, and broader and thinner at either end. The SCM is also a primary landmark of the neck, dividing it into anterior and posterior cervical triangles, which helps define the location of structures such as the lymph nodes for the head and neck. Its length and complexity make it vulnerable to strain and injury, especially when performing repeated motions or activities that require maintaining an uncomfortable posture for long periods.
Occupations such as violinists, painters, and carpenters can strain the SCM muscle over time due to the nature of their work. Additionally, activities such as weightlifting, swimming with an incorrect style, and performing sit-ups too abruptly can also strain the SCM. Poor posture, aging, pillow height, frequent sleeping on the stomach, neck trauma (whiplash), anxiety, and stress can also contribute to SCM strain and injury.
SCM syndrome is a condition that can develop due to the SCM muscle's tightness, sensitivity, or trigger points. This condition can cause neck stiffness, pain, and other symptoms such as headaches, dizziness, and balance problems. To prevent SCM strain and injury, it is important to maintain good posture, practice daily neck stretches, and manage stress through techniques such as meditation, relaxation, yoga, and light exercises.
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The muscle is closely related to important neurovascular structures
The sternocleidomastoid muscle is a two-headed neck muscle that attaches to the manubrium of the sternum, the clavicle, and the mastoid process of the temporal bone. It is a long, bilateral muscle of the neck that can be easily seen and felt. It functions to flex the neck both laterally and anteriorly, as well as rotate the head to the opposite side of contraction.
The sternocleidomastoid muscle also has a significant relationship with the cervical plexus, which supplies sensation, including proprioception, to the muscle. The cervical plexus merges dorsally to the muscle at Erb's point (punctum nervosum), which is an important landmark for medical procedures such as local anaesthesia and central venous catheterization. Additionally, the superior thyroid artery, a branch of the external carotid artery, provides blood supply to the sternocleidomastoid muscle.
Furthermore, the sternocleidomastoid muscle acts as a protective barrier for vital structures in the neck. It safeguards the vertical neurovascular bundle, branches of the cervical plexus, deep cervical lymph nodes, and soft tissues of the neck from potential damage. This muscle also serves as a primary landmark for the neck, dividing it into anterior and posterior cervical triangles. This division helps define the location of structures such as the lymph nodes in the head and neck region.
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Frequently asked questions
The sternocleidomastoid (SCM) muscle is a two-headed neck muscle that allows you to bend your neck and turn or tilt your head.
The sternocleidomastoid muscle helps you bend your neck, rotate your head to the opposite side, and flex your neck laterally and anteriorly. It also aids in respiration and helps maintain posture.
The sternocleidomastoid muscle is one of the largest and most superficial cervical muscles, making it easily visible and palpable. It serves as a primary landmark of the neck.
The sternocleidomastoid muscle originates from two locations: the manubrium of the sternum (sterno-) and the clavicle (cleido-). It inserts at the mastoid process of the temporal bone of the skull (-mastoid).
Injuries, sprains, strains, atrophy, and tumors can affect the SCM muscle. Sternocleidomastoid syndrome is a condition involving neck stiffness, pain, and trigger points. Torticollis, or wryneck, can cause the head to tilt to one side due to shortened SCM muscles.
