Sternocleidomastoid (left) (Musculus sternocleidomastoideus)
Educational content only — not medical advice.
Anatomy
The neck’s most prominent muscle: a strong strap running obliquely from sternum and clavicle to the mastoid, dividing the neck into anterior and posterior triangles — the surgeon’s master landmark.
Origin & insertion
Sternal head from the manubrium front; clavicular head from the clavicle’s medial third.
Action
Rotates the head to the opposite side and tilts it to its own; bilateral contraction lifts the head from lying — the classic muscle test.
Innervation
Spinal accessory nerve (CN XI) with sensory branches from C2–C3.
Clinical notes
Congenital shortening (infant torticollis) responds to early stretching; accessory-nerve injury during posterior-triangle node biopsy paralyses the shoulder with a drooping contour.
Related structures
Educational references
FAQ
What is the role of the Sternocleidomastoid (left)?
The neck’s most prominent muscle: a strong strap running obliquely from sternum and clavicle to the mastoid, dividing the neck into anterior and posterior triangles — the surgeon’s master landmark.
Why is the Sternocleidomastoid (left) clinically important?
Congenital shortening (infant torticollis) responds to early stretching; accessory-nerve injury during posterior-triangle node biopsy paralyses the shoulder with a drooping contour.
Source & license
BodyParts3D, © The Database Center for Life Science licensed under CC Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/). license details