Logan Steele
The sternocleidomastoid muscle is a neck muscle that helps with head rotation, head tilt, and pointing the chin towards the breastbone. It originates from the sternal manubrium and medial aspect of the clavicle and attaches to the mastoid process of the temporal bone and superior nuchal line. It is innervated by the accessory nerve, which arises within the spinal column from the ventral roots of the motor fibres of the upper five cervical segments. The sternocleidomastoid is one of the largest and most superficial cervical muscles and is an important landmark of the neck.
| Characteristics | Values |
|---|---|
| Location | The neck |
| Shape | Cylindrical, strap-like |
| Appearance | Thick and narrow in the centre, broader and thinner at the ends |
| Composition | Two heads, separated by a triangular interval |
| Blood Supply | Overlying skin paddle |
| Artery | Occipital, Superior Thyroid |
| Nerve | Accessory, Spinal Accessory |
| Functions | Rotation of the head, flexion of the neck, assists breathing, maintains neck posture, helps the temporomandibular joint function |
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What You'll Learn
Sternocleidomastoid muscle origin
The sternocleidomastoid muscle is a two-headed neck muscle that is easily visible and palpable. It is one of the largest and most superficial cervical muscles. The muscle is thick and broad at the ends and narrow in the centre. The sternocleidomastoid muscle is named so because it 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. The muscle is attached above by a short tendon into the lateral surface of the mastoid process and to the lateral half of the superior nuchal line of the occipital bone.
The sternocleidomastoid has two heads that originate from two locations: the manubrium of the sternum and the clavicle. The sternal head is the medial and more superficial division of the muscle, while the clavicular head is the lateral and deeper division. The clavicular head originates from the medial third of the superior border of the anterior surface of the clavicle. The sternal head originates from the upper part of the front of the manubrium sterni. The two heads are separated from one another at their origins by a triangular interval (lesser supraclavicular fossa) but gradually blend, below the middle of the neck, into a thick, rounded muscle.
The sternocleidomastoid muscle plays an important role in tilting and rotating the head, as well as other movements. It is also an accessory muscle of inspiration. The motor component of the muscle is from the accessory nerve and the sensory innervation is from the cervical plexus. The SCM becomes chronically shortened in cases of torticollis, a movement disorder in which the head is persistently turned to one side.
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Sternocleidomastoid muscle insertion
The sternocleidomastoid muscle (SCM) is a two-headed neck muscle that binds the skull to the sternum and clavicle. It is a bilateral muscle of the neck, which functions to flex the neck both laterally and anteriorly, as well as rotate the head contralaterally to the side of contraction. The SCM is a unique muscle, in terms of variations at its origin.
The SCM is a large, easily recognisable, and palpable muscle. It is an important landmark in the neck which divides it into an anterior and a posterior triangle. The muscle originates from the upper edge of the sternal manubrium and the medial quarter of the upper face of the clavicle. The two muscle heads merge into a single muscle belly that is directed upwards and laterally.
The SCM has dual innervation and multiple functions. It is innervated by the accessory nerve (cranial nerve XI) and direct branches of the cervical plexus (C2-C3). The SCM is supplied by the occipital artery and superior thyroid artery. It functions to flex the neck (when both sides are activated), extends the head, and rotates the head. It is also an accessory muscle of inspiration. The motor component of the muscle is from the accessory nerve and the sensory innervation is from the cervical plexus.
The SCM can also have inspiratory muscle action by taking a fixed point on the temporal bone and then lifting the sternum and the clavicles. It plays an important role in the posture of the neck and the body. It has been shown that vestibular stimulation electrically activates the sternocleidomastoid, with evidence of a close connection between the vestibular area and the motoneurons of the SCM.
The insertion of the SCM is at the mastoid process of the temporal bone of the skull. The muscle is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone.
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Sternocleidomastoid muscle function
The sternocleidomastoid muscle is a two-headed neck muscle that originates from the manubrium of the sternum and the clavicle, and attaches to the mastoid process of the temporal bone and the superior nuchal line of the occipital bone. It is a thick, strap-like muscle that emerges from the side of the neck and is easily visible and palpable. The sternocleidomastoid muscle has multiple functions, including:
Head Rotation and Tilt
The primary function of the sternocleidomastoid muscle is to rotate the head to the opposite side and tilt the head. When acting unilaterally, it tilts the head toward the same side and rotates the face to the opposite side.
Neck Flexion and Extension
The muscle also contributes to neck flexion, particularly when both sides of the muscle act together. In this case, it also extends the head. Additionally, when acting together with the upper trapezius muscle, it laterally bends the neck, drawing the ear toward the same side.
Accessory Muscle of Inspiration
The sternocleidomastoid muscle is also involved in inspiration or breathing. When the head is fixed, it lifts the sternum and clavicle, expanding the thoracic cavity and facilitating inspiratory breathing.
Maintaining Neck Posture
It plays a role in maintaining neck posture and helping the temporomandibular joint (TMJ) function correctly.
Landmark Structure
The muscle serves as a primary landmark of 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 regions.
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Sternocleidomastoid muscle anatomy
The sternocleidomastoid muscle is a two-headed neck muscle that originates from two locations: the manubrium of the sternum (sterno-) and the clavicle (cleido-). It is a long, bilateral muscle that is easily visible and palpable. It functions to flex the neck both laterally and anteriorly, as well as rotate the head to the opposite side.
The sternocleidomastoid has a cylindrical, strap-like shape that emerges from the side of the neck and tapers at the ends. It runs diagonally from both the collarbone and the breastbone to the back of the head, dividing the neck musculature into anterior (front) and posterior (back) triangles. This muscle is innervated by the spinal accessory nerve (CN XI) or cranial nerve 11, which arises from the ventral roots of the upper five cervical segments within the spinal column. The motor nerve fibres then ascend through the foramen magnum and descend through the jugular foramen, uniting with sensory fibres from the anterior primary division of the second and sometimes third cervical nerves.
The sternocleidomastoid has two heads: the sternal (or medial) head and the clavicular (or lateral) head. The sternal head originates from the manubrium of the sternum, while the clavicular head originates from the clavicle along its superior surface. A small triangular space, the lesser supraclavicular fossa, separates these two attachments. The two heads gradually blend below the middle of the neck into a thick, rounded muscle, which is inserted into the lateral surface of the mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone.
The sternocleidomastoid is covered by the superficial investing cervical fascia, with the external jugular vein and platysma muscle lying superficial to it. Cutaneous nerves from the anterior rami of the cervical plexus, including the greater auricular and transverse cervical nerves, sit over the sternocleidomastoid muscle. The posterior border of the parotid gland overlaps the muscle near its superior attachment, and the muscle conceals much of the carotid sheath and its contents. The accessory nerve (CN XII) passes deep to the sternocleidomastoid muscle before turning posteriorly towards the trapezius muscle.
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Sternocleidomastoid muscle innervation
The sternocleidomastoid muscle is a two-headed neck muscle that 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. It is one of the largest and most superficial cervical muscles, and is easily visible and palpable. The sternocleidomastoid muscle has a cylindrical, strap-like shape that emerges from the side of the neck and tapers at the ends.
The sternocleidomastoid muscle is innervated by the accessory nerve (cranial nerve XI), which arises from the ventral roots of the motor fibres of the upper five cervical segments within the spinal column. The motor nerve fibres ascend through the foramen magnum and then descend through the jugular foramen, where they unite with sensory fibres from the anterior primary division of the second and sometimes third cervical nerves. The accessory nerve supplies only motor fibres, while the cervical plexus (C2-C3) supplies sensation, including proprioception.
The sternocleidomastoid muscle has dual innervation and multiple functions. It is involved in head rotation, head tilt, pointing the chin towards the breastbone, and assisting in breathing. When acting unilaterally, the sternocleidomastoid muscle tilts the head towards the ipsilateral side while rotating the face to the contralateral side. When acting together with the upper trapezius, it laterally bends the neck, drawing the ear towards the ipsilateral shoulder. It also acts in conjunction with the scalene and trapezius muscles to compensate for head tilt due to postural distortion.
The sternocleidomastoid muscle can become chronically shortened in cases of torticollis, a movement disorder characterised by the persistent turning of the head to one side. Impairment or injury to the spinal accessory nerve can result in weakness or paralysis of the sternocleidomastoid muscle, leading to atrophy and difficulty in turning the head and bending the neck. Treatment for this condition involves strengthening exercises for the muscle and, if possible, repair of the nerve.
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Frequently asked questions
The sternocleidomastoid muscle is located in the neck. 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 sternocleidomastoid muscle has two heads. One originates from the collarbone/clavicle and the other from the breastbone/manubrium. The muscle is thick and narrow at its centre, and broader and thinner at either end.
The sternocleidomastoid muscle helps with head rotation, head tilt, and pointing the chin towards the breastbone. It also assists in breathing, maintaining neck posture, and helping the temporomandibular joint (TMJ) function.
The sternocleidomastoid muscle is innervated by the accessory nerve (cranial nerve XI). It receives a signal from the accessory nerve nucleus in the anterior horn of the spinal cord, which causes an action potential to travel along the muscle fibre, resulting in a contraction of the muscle.
