Definition

Noun 1. A major neck muscle: The sternocleidomastoideus is one of a pair of large, thick, superficial muscles located on each side of the neck. It originates from the sternum (breastbone) and clavicle (collarbone) and inserts into the mastoid process of the temporal bone and the occipital bone of the skull. 2. A muscle with specific functions: Its primary actions are to rotate the head obliquely to the opposite side and to tilt the head toward the same side. When both muscles (the left and right) contract together, they flex the neck forward and can assist in extending the head at the atlanto-occipital joint.

Usage Examples

• The sternocleidomastoideus is easily visible and palpable when the head is turned to one side against resistance.
• Pain in the sternocleidomastoideus is a common cause of tension headaches and neck stiffness.
• To examine the sternocleidomastoideus, the clinician asks the patient to turn their head to the opposite side while applying gentle resistance.

Advanced Usage

• Clinical significance: The sternocleidomastoideus is a key landmark for anatomical divisions of the neck (e.g., the anterior and posterior triangles). It is also clinically important in conditions like torticollis (wry neck), where spasm or shortening of this muscle causes an abnormal head posture.
• In anatomical description: The muscle is often referenced by its full name in formal medical and anatomical contexts to specify its precise origins and insertions.

Variants and Related Words

• Sternocleidomastoid (SCM): This is the more common and abbreviated term used in both clinical practice and general anatomy. It is functionally synonymous with "sternocleidomastoideus."
  • Example: The physiotherapist massaged the patient's tight sternocleidomastoid muscle.

Synonyms

• Sternomastoid: An older, less precise term that references only the sternal origin.
• SCM muscle: A standard clinical abbreviation.

Related Phrases

• To palpate the sternocleidomastoid: To examine the muscle by feeling it with the fingers.
  • The doctor palpated the sternocleidomastoid to check for tenderness or swelling.
• Sternocleidomastoid region: The area of the neck where this muscle is located.

Noun

1. one of two thick muscles running from the sternum and clavicle to the mastoid and occipital bone; turns head obliquely to the opposite side; when acting together they flex the neck and extend the head