Section 01 of 20
Introduction
Sternocleidomastoid, often called SCM, is a thick, prominent muscle that runs diagonally across each side of the front of the neck, from the breastbone and collarbone up to the skull behind the ear. It is one of the most visible neck muscles and stands out clearly when the head turns.
It has two heads at its lower attachment, a rounded sternal head and a flatter clavicular head, which merge into a single muscle belly. The two sternocleidomastoid muscles, left and right, work together and separately to move the head and neck in several directions.
Section 02 of 20
Origin
| Origin | Sternal head: the front of the manubrium of the sternum. Clavicular head: the medial third of the clavicle. |
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Section 03 of 20
Insertion
| Insertion | The mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone. |
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Section 04 of 20
Actions
| Primary action | Opposite-side rotation of the head. |
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| Secondary actions | Same-side lateral flexion, neck flexion (both sides), and assisting forceful inhalation. |
| Movement at the joint | Cervical spine and the atlanto-axial and atlanto-occipital joints. |
| Heads / fiber groups | Two heads: sternal and clavicular. |
| Functional examples | Turning to look over the shoulder; tilting the head; lifting the head from lying down; forceful breathing during exercise. |
Rotation of the head
One side turns the face toward the opposite side.
Lateral flexion of the neck
One side tilts the head toward the same shoulder.
Flexion of the neck
Both sides together flex the lower neck and can help flex the head, depending on the starting position.
Assisting inhalation
With the head fixed, both sides help raise the sternum during forceful or labored breathing.
Section 05 of 20
Nerve Innervation
| Nerve | The accessory nerve (cranial nerve XI), with sensory and proprioceptive contributions from the anterior rami of C2–C3. |
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The accessory nerve travels through the upper part of the muscle before continuing to the trapezius, and the internal jugular vein, carotid artery, and cervical lymph nodes lie just beneath and beside it. Neck swelling, hoarseness, or shoulder-shrug weakness may reflect nerve, vascular, or lymphatic involvement, not only muscle tightness.
Section 06 of 20
Blood Supply
| Blood | The occipital artery and the superior thyroid artery, both branches of the external carotid artery. |
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Section 07 of 20
Pictures and Visual Anatomy
Section 08 of 20
Functional Movement
Sternocleidomastoid is used constantly for turning the head to look around, tilting the head, and lifting the head from a lying position. Both sides working together also assist forceful breathing during exercise or respiratory illness.
Section 09 of 20
Synergists and Antagonists
Synergists: the scalenes and the opposite-side sternocleidomastoid (rotation), and the deep neck flexors (longus colli and longus capitis) for neck flexion. Antagonists: the splenius and semispinalis capitis and cervicis muscles (extension and opposite rotation), and the opposite-side sternocleidomastoid for lateral flexion and rotation.
Section 10 of 20
Palpation and Location
Client position and technique
Position the client supine with the head slightly turned to the opposite side. Ask the client to lift the head slightly off the table or gently turn the head against light resistance to make the muscle stand out, then follow it from behind the ear down to the sternum and clavicle with a gentle pincer grip.
Protect nearby structures
The carotid artery, jugular vein, vagus nerve, and lymph nodes lie deep to and beside the muscle. Never press on the front of the neck near the carotid pulse, use light to moderate pressure only, avoid sustained bilateral pressure, and stop if the client reports dizziness, difficulty swallowing, or tingling.
Section 11 of 20
Massage Therapy Relevance
Sternocleidomastoid is commonly involved in neck and headache complaints, particularly with forward head posture, whiplash, and stress-related tension. Because of the sensitive structures nearby, technique and consent are especially important in this area.
Section 12 of 20
Dysfunction: What Happens When Movement Goes Wrong
Changes in how a muscle works can change how a joint moves. The points below describe possibilities that may be associated with altered muscle function; they are not diagnoses, and one muscle is never assumed to be the sole cause of a problem.
When the muscle is weak
Weakness may reduce head rotation control and may be associated with compensatory use of the scalenes and upper trapezius.
When it is tight or shortened
Tightness may be associated with a head tilt, limited rotation to the opposite side, and tension headaches.
When it is overused
Prolonged screen use, stress-related tension, and repetitive rotation may overload the muscle and may contribute to neck and head pain.
When it is strained
A strain, such as from whiplash, may cause neck pain, stiffness, and sometimes dizziness or headache; vestibular and cervical spine problems can look similar.
When it is inhibited or others compensate
Reduced activation may be associated with less controlled head rotation and more work by the scalenes and upper trapezius.
When it does not coordinate well with synergists and antagonists
Poor coordination with the scalenes, splenius, and deep neck flexors may alter head and neck control and may be associated with neck and head symptoms.
Section 13 of 20
Conditions, Pathologies, and Pain Relationships
Whiplash-associated strain
Sudden neck movement, as in a vehicle collision, can strain sternocleidomastoid and cause neck pain, stiffness, and sometimes headache or dizziness.
Tension-type headache and trigger points
Tender points in the muscle may refer pain to the forehead, around the eye, and the top of the head, though headache has many possible causes.
Torticollis
A shortened or spasming sternocleidomastoid can hold the head tilted and rotated to one side; congenital torticollis in infants needs medical assessment.
Differential considerations
Cervical disc and facet joint problems, vestibular (inner ear) disorders, thyroid or lymph node conditions, and vascular problems can all cause similar neck and head symptoms.
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Example Clinical Relationship
A client involved in a low-speed car collision reports neck pain, stiffness, and an occasional dull headache over the following days. Sternocleidomastoid may be involved, and the pattern may be associated with a whiplash-related strain, but cervical spine, vestibular, and vascular problems can look similar and need assessment. Gentle work along the muscle may support comfort once cleared, while dizziness, vision changes, or difficulty swallowing needs referral.
Section 15 of 20
Massage and Treatment Approaches
For healthy, non-acute tissue, position the client supine with the head supported and slightly turned away. Use a very light pincer grip along the muscle belly, avoiding the front of the neck near the trachea and carotid pulse, and consider gentle neck rotation and side-bending within comfort.
| Movement | Use gentle, slow neck rotation and side-bending within comfort; never force the neck or hold pressure while the client swallows. |
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| Regional work | Consider the scalenes, upper trapezius, splenius capitis, and the suboccipitals when assessment supports it. |
| Avoid | Direct pressure over the carotid pulse or trachea, prolonged pressure on both sides at once, and any point that reproduces dizziness or swallowing difficulty. |
Section 16 of 20
Precautions and Contraindications
Precautions and contraindications
- Recent neck injury or whiplash, suspected fracture, or instability.
- Use caution with known carotid or vertebral artery disease, thyroid conditions, or swollen lymph nodes.
- Never apply sustained pressure to both sides of the neck at the same time.
- Stop if pressure causes dizziness, difficulty swallowing or breathing, or tingling.
Section 17 of 20
Red Flags and When to Refer
Red flags and referral
- Sudden severe headache or neck pain, dizziness, vision changes, slurred speech, or facial numbness.
- Difficulty swallowing or breathing, or a rapidly swelling neck.
- A hard, painless lump in the neck, or unexplained weight loss.
- Neck pain with fever and stiffness, or after significant trauma.
Section 18 of 20
Study Summary
Attachments
Origin: manubrium of the sternum and medial clavicle. Insertion: mastoid process and lateral superior nuchal line.
Actions
Rotates the head to the opposite side; laterally flexes to the same side; flexes the neck; assists inhalation.
Supply
Accessory nerve (CN XI), with C2–C3 sensory fibers; occipital and superior thyroid arteries.
Section 19 of 20
Instructor Narration
Open narration transcript
Sternocleidomastoid is the prominent, two-headed muscle that crosses diagonally from the front of the chest to the base of the skull.
The sternal head arises from the manubrium and the clavicular head from the medial clavicle; together they insert on the mastoid process and the lateral superior nuchal line.
One side turns the face to the opposite side and tilts the head to the same side; both sides flex the neck and assist forceful breathing. The scalenes help it, and splenius and semispinalis oppose it.
The accessory nerve, cranial nerve eleven, supplies it, with sensory fibers from C2 and C3, and the occipital and superior thyroid arteries provide its blood.
Palpate with the client supine, turning the head slightly to make the muscle stand out, then use a gentle pincer grip from behind the ear to the sternum and clavicle. Never press on the carotid pulse, and avoid pressure on both sides at once.
Whiplash strain, tension headache, and torticollis are common, and disc, vestibular, thyroid, and vascular problems can overlap. Refer sudden severe headache with dizziness or vision changes, difficulty swallowing or breathing, a hard painless neck lump, or neck pain with fever and stiffness.
Remember: sternum and clavicle to the mastoid process; opposite-side rotation with same-side lateral flexion; accessory nerve.
Section 20 of 20