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    From Musculoskeletal System

    Levator Ani
    Pelvic floor muscle responsible for lifting the anus.
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Lumbar Vertebrae (L1 - L5)
    Vertebrae in the lower back (L1-L5).
    Palatine Bones
    Bones forming part of the hard palate and nasal cavity.
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Cranial Bones
    Bones of the skull that protect the brain.
    Coccyx
    Tailbone, the remnant of the tail in humans.
    Diaphragm
    Primary muscle for breathing.
    Sternum
    Breastbone located in the center of the chest.
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Skull
    Bony structure of the head that encases the brain.
    Ischium
    Part of the pelvis that supports weight while sitting.
    Occipital Bone
    Bone forming the back and base of the skull.
    Thoracic Cage
    Ribs and sternum forming the protective cage for the heart and lungs.
    Ellipsoidal (Condyloid) Joints
    e.g., wrist
    Ulna
    Forearm bone on the pinky side.
    Patella
    Knee cap, protecting the knee joint.
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Vertebral Column
    Spinal column consisting of vertebrae.
    Ilium
    Uppermost and largest part of the hip bone.
    Facial Bones
    Bones forming the structure of the face.

    Sternocleidomastoid

    Reviewed by our medical team

    Muscle that rotates and flexes the neck.

    1. Overview

    The sternocleidomastoid (SCM) is a prominent, paired muscle located in the anterolateral aspect of the neck. It plays a vital role in head and neck movement and serves as an important anatomical landmark for clinical examination and surgical procedures. The name of the muscle reflects its attachments: sternum (sterno), clavicle (cleido), and mastoid process (mastoid).

    2. Location

    The sternocleidomastoid is found in the superficial layer of the neck, spanning from the base of the skull to the thorax:

    • Superiorly: Inserts on the mastoid process of the temporal bone and the lateral half of the superior nuchal line of the occipital bone.

    • Inferiorly: Arises from two heads:

      • Sternal head: Manubrium of the sternum.

      • Clavicular head: Medial third of the clavicle.

    • Deep to: External jugular vein and superficial cervical fascia.

    3. Structure

    The sternocleidomastoid is a thick, fusiform muscle with two heads that blend to form a single belly:

    • Muscle type: Skeletal, voluntary muscle.

    • Innervation: Spinal accessory nerve (cranial nerve XI) for motor function, with sensory input from C2 and C3 (cervical plexus).

    • Blood supply: Branches of the occipital artery, superior thyroid artery, and suprascapular artery.

    • Orientation: Oblique, running upward and laterally from the thoracic region to the base of the skull.

    4. Function

    The sternocleidomastoid muscle controls several important head and neck movements:

    • Unilateral contraction:

      • Rotates the head to the opposite side.

      • Tilts the head to the same side (lateral flexion).

    • Bilateral contraction:

      • Flexes the neck and brings the chin toward the chest.

      • Assists in elevation of the sternum and clavicle during forced inspiration.

    5. Physiological role(s)

    Beyond basic movement, the SCM contributes to several physiological and postural roles:

    • Head and neck stabilization: Helps maintain balance and proper orientation of the head.

    • Breathing assistance: Acts as an accessory muscle during labored or deep breathing.

    • Proprioception: Contains receptors that relay information on head position, aiding in balance and spatial orientation.

    • Surface landmark: Defines important triangles of the neck—anterior and posterior triangles—used in clinical and surgical assessments.

    6. Clinical Significance

    The sternocleidomastoid is involved in various clinical scenarios:

    • Torticollis (wry neck):

      • Condition characterized by abnormal, involuntary contraction of the SCM, causing head tilt and rotation.

      • Can be congenital (due to fibrous shortening of SCM) or acquired (due to muscle spasm or nerve injury).

    • Accessory nerve injury:

      • Damage to cranial nerve XI can impair SCM function, leading to weakness in head rotation and shoulder elevation (trapezius involvement).

    • Muscle strain:

      • Common in whiplash injuries or poor posture, resulting in pain and stiffness along the side of the neck.

    • Palpation landmark:

      • Useful in locating carotid pulse, internal jugular vein, and cervical lymph nodes during physical examination.

    • Referred pain:

      • Trigger points in the SCM can refer pain to the jaw, ear, or around the eye, mimicking other conditions.

    Did you know? Your spinal cord is protected by the vertebral column.