GENERAL INFORMATION
The Sternocleidomastoid (SCM) muscle is a prominent and vital component of the neck’s anatomy, easily recognisable due to its distinctive V-shape. This muscle is crucial not only for various movements of the head but also for respiratory mechanics. As a superficial muscle, it significantly influences neck contour and aesthetics. The SCM’s function and visibility make it an important muscle in both health and disease, impacting everything from physical posture to conditions affecting cervical mobility.
ORIGIN
The Sternocleidomastoid has two heads of origin:
- The sternal head originates from the top of the manubrium of the sternum.
- The clavicular head originates from the upper surface of the medial third of the clavicle.
INSERTION POINT
The Sternocleidomastoid muscle inserts at the mastoid process of the temporal bone and the lateral portion of the superior nuchal line of the occiput. This dual insertion enables the SCM to coordinate complex movements of the head and neck effectively.
MAJOR ARTERIES
The SCM receives its blood supply primarily from the occipital artery and branches of the external carotid artery. This robust vascularisation supports the muscle’s active role in neck movement and posture maintenance.
NEURAL INNERVATION
Innervated by the accessory nerve (cranial nerve XI), with sensory fibres from the cervical plexus (C2-C3), the SCM exhibits a wide range of movements from head rotation to slight flexion, essential for many daily activities and expressive gestures.
TRIGGER POINT
Trigger points in the Sternocleidomastoid can be a source of significant discomfort, causing symptoms such as headaches, dizziness, and peculiar sensations like a sore throat or fullness in the ear. These symptoms are often misleading, leading to challenges in diagnosis.
CONCENTRIC FUNCTION
When contracting concentrically, the SCM rotates the head to the opposite side and flexes the neck laterally to the same side. It also plays a role in elevating the sternum during deep inhalation, assisting the respiratory process.
ECCENTRIC FUNCTION
Eccentrically, the SCM helps to slow or control the movement as the head returns to a central position from being rotated or tilted. This modulation is crucial for activities that involve quick head movements, providing stability and preventing injury.
ISOMETRIC FUNCTION
Isometrically, the sternocleidomastoid stabilises the head and neck, supporting the cervical spine during activities that require a fixed head position, such as driving or working at a computer. This stabilisation is vital for maintaining a healthy neck posture and preventing strain.
RELATED MUSCLE-SCIENTIFIC NAMES
- Trapezius: Supports the neck and shoulders, working synergistically with the SCM.
- Scalenes: Assist in neck flexion and lateral rotation, complementing the actions of the SCM.
- Levator Scapulae: Elevates the scapula, coordinating with the SCM for neck and shoulder movements.
- Splenius Muscles: Act as antagonists to the SCM during certain neck movements.
ANTAGONIST
- Trapezius: Particularly during neck extension, where it opposes the SCM.
- Scalenes: Counteract the sternocleidomastoid’s actions during opposite-side neck rotation.
- Deep Neck Flexors: Oppose the SCM during forward neck flexion.
COMMON INJURIES
- Muscle Strain: Common in activities involving sudden head turns or impacts.
- Torticollis (Wry Neck): Involuntary contraction of the sternocleidomastoid causing head tilt, often painful.
- Myofascial Pain: Due to trigger points within the SCM leading to referred pain and tension.
- Compression Syndromes: These include carotid artery compression or cervical nerve compression due to the muscle’s proximity to critical neck structures.
EXERCISES
- Neck Rotation Exercise: Rotate the head slowly to each side, holding for a few seconds to strengthen and mobilise the sternocleidomastoid.
- Resistance Band Neck Rotation: Attach a band to a stationary object at head height and gently pull the band by turning the head, increasing sternocleidomastoid strength.
- Shoulder Shrugs: Lift and lower the shoulders to engage the lower fibres of the sternocleidomastoid, enhancing neck and shoulder stability.
- Upright Rows: Perform with a barbell or dumbbell to indirectly work the SCM and improve upper back and neck posture.
STRETCHES
- SCM Stretch: Gently stretch the muscle by turning the head to one side and tilting it backwards, targeting the sternocleidomastoid for increased flexibility.
- Lateral Neck Stretch: Bend the neck laterally away from the shoulder to stretch the sternocleidomastoid on the opposite side, enhancing muscle length and reducing tension.
- Diagonal Neck Stretch: Combine rotation and lateral flexion to stretch the sternocleidomastoid thoroughly, improving range of motion and relieving tightness.
- Dynamic Neck Warm-Up: Perform gentle neck rotations, side bends, and forward flexions to warm up the sternocleidomastoid before engaging in more strenuous activities.