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The sternocleidomastoid (SCM) is a two-headed neck muscle that originates at two separate points and then converges to insert at one point. It is one of the largest and most superficial cervical muscles, and its primary actions include rotation of the head to the opposite side and flexion of the neck. The SCM plays an important role in tilting the head and turning the neck, and it also acts as an accessory muscle of respiration. The SCM is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3). It is closely related to certain neurovascular structures in the neck and serves as a primary landmark of the neck, dividing it into anterior and posterior cervical triangles.
| Characteristics | Values |
|---|---|
| Muscle Name | Sternocleidomastoid (SCM) |
| Muscle Type | Two-headed muscle |
| Muscle Location | Neck |
| Muscle Shape | Cylindrical, strap-like |
| Muscle Functions | Rotation of the head, head tilt, pointing the chin toward the breastbone, assisting in breathing, maintaining neck posture, helping the temporomandibular joint (TMJ) function, flexing the neck |
| Innervation | Accessory nerve (Cranial nerve XI), direct branches of the cervical plexus (C2-C3) |
| Blood Supply | Superior thyroid artery, a branch of the external carotid artery |
| Related Injuries | Torticollis, whiplash, sternocleidomastoid syndrome |
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What You'll Learn
The sternocleidomastoid is a two-headed neck muscle
The sternocleidomastoid is one of the largest and most superficial cervical muscles. It is thick and narrow at its centre and broader and thinner at its ends. The muscle is easily visible and palpable, and the carotid pulse may be felt in the middle third of its front edge. It serves as a primary landmark of the neck, dividing it into anterior and posterior cervical triangles.
The muscle originates at the manubrium of the sternum and the clavicle and inserts at the mastoid process of the temporal bone of the skull. The two heads are separated at their origins by a triangular interval (lesser supraclavicular fossa) but blend together below the middle of the neck into a thick, rounded muscle.
The sternocleidomastoid is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3). It receives blood supply through the superior thyroid artery, a branch of the external carotid artery. The muscle plays a central role in the formation of the triangles of the neck and is involved in various complex physiological movements.
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It is innervated by the accessory nerve
The sternocleidomastoid muscle is a two-headed neck muscle, which bears attachments to the manubrium of the sternum, the clavicle, and the mastoid process of the temporal bone. It is one of the largest and most superficial cervical muscles. The primary actions of the muscle are the rotation of the head to the opposite side and the flexion of the neck.
The sternocleidomastoid muscle is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3). The accessory nerve is the eleventh paired cranial nerve, and it has a purely somatic motor function. It innervates the sternocleidomastoid and trapezius muscles. The nerve has a double origin and always exits the skull through the jugular foramen. The spinal portion arises from neurons of the upper spinal cord, specifically C1-C5/C6 spinal nerve roots. These fibres then combine to form the spinal part of the accessory nerve, which then travels upward to enter the cranial cavity through the foramen magnum.
The accessory nerve is essential for neck and shoulder movement, as well as the intrinsic musculature of the larynx and the sensitive afferences of the trapezius and sternocleidomastoid musculature. It is also involved in the correct movement of the vocal cords. The nerve can be damaged by daily movements or behaviours that exceed its elastic capacity, such as excessive stretching or carrying heavy weights. These types of injuries are generally benign. However, more serious injuries can occur if a patient undergoes extensive tumour mass-removal surgery in the neck area, resulting in a lack of blood nutrition or partial removal of the nerve.
The sternocleidomastoid muscle can be examined by asking the patient to rotate their head and shrug their shoulders, both normally and against resistance. This examination can reveal signs of muscle wasting in the sternocleidomastoid and trapezius in cases of long-standing nerve damage.
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It originates at the manubrium of the sternum and the clavicle
The sternocleidomastoid muscle is a two-headed neck muscle that gets its name from its points of attachment: the manubrium of the sternum (sterno-), the clavicle (-cleido-), and the mastoid process of the temporal bone (-mastoid). It is a long, bilateral muscle of the neck that is easily visible and palpable.
The sternocleidomastoid muscle originates from two locations: the manubrium of the sternum and the clavicle. The sternal head, which is tendinous in front and fleshy behind, arises from the upper part of the front of the manubrium sterni. It travels superiorly, laterally, and posteriorly. The clavicular head, on the other hand, is composed of fleshy and aponeurotic fibres and arises from the upper, frontal surface of the medial third of the clavicle. It is directed almost vertically upward.
The two heads of the muscle are separated from each other at their origins by a triangular interval (lesser supraclavicular fossa) but gradually blend below the middle of the neck into a thick, rounded muscle. This muscle then inserts by a strong tendon into the lateral surface of the mastoid process and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone.
The sternocleidomastoid muscle is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3). It plays a central role in the formation of the triangles of the neck, dividing it into anterior and posterior cervical triangles. It is also involved in the flexion of the neck and rotation of the head to the opposite side.
The sternocleidomastoid muscle is an important landmark in the neck region and is associated with various neuromuscular pathologies such as torticollis. It is also used as an anatomical reference for certain medical procedures, such as central venous catheterization.
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It has an insertion at the mastoid process of the temporal bone
The sternocleidomastoid muscle is a two-headed neck muscle that gets its name from its points of attachment: the manubrium of the sternum ("sterno-"), the clavicle ("-cleido-"), and the mastoid process of the temporal bone ("-mastoid"). The muscle is easily visible and palpable, and it plays a crucial role in neck posture and movement.
The sternocleidomastoid muscle has an insertion at the mastoid process of the temporal bone. This insertion point is a key structural feature that contributes to the muscle's function in neck movement and posture. The mastoid process is a prominent bony landmark located behind the ear on the skull. It is part of the temporal bone, which is one of the bones that make up the skull.
The insertion of the sternocleidomastoid muscle at the mastoid process allows for the muscle's bilateral contraction, which results in the elevation of the head and dorsal extension of the upper cervical joints. This bilateral contraction also causes a flexion of the lower cervical column, leading to an overall bending of the neck towards the chest. This movement is essential for maintaining neck posture and facilitating various physiological movements.
The sternocleidomastoid muscle's insertion at the mastoid process of the temporal bone is also crucial for its role in rotating the head to the opposite side of the contracting muscle. This unilateral contraction of the sternocleidomastoid muscle flexes the cervical vertebral column to the same side while rotating the head to the opposite side. This movement is often observed when a person moves their head to the opposite side, and it is an important aspect of the muscle's function in neck rotation.
The insertion of the sternocleidomastoid muscle at the mastoid process is facilitated by a strong tendon and a thin aponeurosis. This insertion point is essential for the muscle's ability to function as an inspiratory muscle. By taking a fixed point on the temporal bone, the sternocleidomastoid muscle can lift the sternum and clavicle, expanding the thoracic cavity and aiding in respiration. This demonstrates the muscle's versatility and importance in maintaining respiratory function.
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It is an important landmark in the neck
The sternocleidomastoid muscle is a two-headed neck muscle that is easily visible and palpable. It is innervated by the accessory nerve and is one of the largest and most superficial cervical muscles. It originates at the manubrium of the sternum and the clavicle and has an insertion at the mastoid process of the temporal bone of the skull.
The muscle is an important landmark in the neck as it divides the neck into anterior and posterior cervical triangles. These triangles help 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 sternocleidomastoid 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. The common carotid artery, accessory nerve, and brachial plexus are some of the important structures related to the sternocleidomastoid. The carotid pulse can be felt in the middle third of the front edge of the sternocleidomastoid.
The muscle also plays a role in the posture of the neck and the body. It has been shown that vestibular stimulation electrically activates the sternocleidomastoid, indicating a close connection between the vestibular area and the motoneurons of the SCM. The lateral inclination is the movement with which the SCM expresses its maximum capacity for speed and force.
The sternocleidomastoid is also important in 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 triangle formed by the clavicle and the sternal and clavicular heads of the sternocleidomastoid muscle is used as a landmark in identifying the correct location for central venous catheterization.
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Frequently asked questions
The sternocleidomastoid (SCM) is a muscle in the neck region, often classified with the lateral cervical muscles. It is a two-headed neck muscle that originates at the manubrium of the sternum and the clavicle.
The SCM helps with functions such as head rotation, head tilt, and pointing the chin toward the breastbone. It also assists in breathing, maintaining neck posture, and helping the temporomandibular joint (TMJ) function.
The sternocleidomastoid muscle originates from two locations: the manubrium of the sternum and the clavicle.
The SCM converges into one point and inserts on the lateral surface of the mastoid process and the nuchal line of the occipital bone.
The SCM's main function is to move the vertebral column and head. It also acts as an accessory muscle of respiration, along with the scalene muscles of the neck.
