13/01/2026
Sternocleidomastoid is a large, superficial neck muscle that plays a key role in head movement, posture, breathing assistance, and clinical assessment. Because it is easily visible and palpable, it is also one of the most examined neck muscles in practice.
Origin
√The SCM has two heads:
√Sternal head: anterior surface of the manubrium of the sternum
√Clavicular head: medial one third of the clavicle
Insertion
√Mastoid process of the temporal bone
√Lateral half of the superior nuchal line of the occipital bone
Structure
√The two heads merge and run obliquely upward and backward
√Forms a clear surface landmark dividing the neck into anterior and posterior triangles
Supply
√Spinal accessory nerve (CN XI) for motor function
√Sensory input from C2–C3 via cervical plexus
√Injury to CN XI leads to weakness in head rotation and difficulty maintaining head posture.
Supply
√Branches of:
√Occipital artery
√Superior thyroid artery
√Unilateral Contraction
√Ipsilateral lateral flexion of the neck
√Contralateral rotation of the head
Example: Right SCM rotates the head to the left and bends it to the right.
√Bilateral Contraction
√Neck flexion
√Assists in head extension when acting from flexed position
√Elevates sternum and clavicle during forced inspiration
Role
√Maintains head posture against gravity
√Assists visual and vestibular orientation
√Acts as an accessory muscle of respiration in COPD, asthma, and labored breathing
and Surface Anatomy
√Ask the patient to rotate the head against resistance
√The SCM becomes prominent and easy to palpate
√Runs from behind the ear to the sternum and clavicle
Significance
1. Postural Dysfunction
√Commonly overactive and tight in forward head posture
√Often associated with upper crossed syndrome
2. Neck Pain and Headache
√Trigger points can refer to pain:
√Head and temple
√Behind the eye
√Ear and jaw
3. Torticollis
√Congenital torticollis: unilateral SCM
