Logo

    Related Topics

    From Musculoskeletal System

    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Iliolumbar Ligament
    Ligament connecting the ilium and lumbar vertebrae.
    Sesamoid Bones
    e.g., patella, some found in hands/feet.
    Trapezius
    Muscle responsible for moving, rotating, and stabilizing the scapula.
    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Acetabulum
    The acetabulum is the pelvic socket that connects with the femoral head to form the hip joint, vital for stability, movement, and weight-bearing.
    Interspinous Ligament
    Spinal ligament between adjacent vertebral spinous processes.
    Ulna
    Forearm bone on the pinky side.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Carpals (8 bones)
    8 wrist bones.
    Skull
    Bony structure of the head that encases the brain.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Hinge Joints
    e.g., elbow, knee
    Sacroiliac Ligaments
    Ligaments connecting the sacrum to the iliac bones.
    Obliques (External and Internal)
    Muscles responsible for torso rotation.
    Pubis
    Part of the pelvis that joins with the opposite side to form the pubic symphysis.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Anterior Cruciate Ligament (ACL)
    Knee ligament that stabilizes the joint.
    Adductors
    Muscles that bring the thighs toward the midline.
    Vomer Bone
    Bone forming the nasal septum.
    Extensor Tendons
    Tendons that help extend the fingers and toes.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Tarsals (7 bones)
    7 ankle bones.

    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 bones are constantly adapting to the mechanical forces placed on them.