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    Related Topics

    From Musculoskeletal System

    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.
    Obliques (External and Internal)
    Muscles responsible for torso rotation.
    Saddle Joints
    e.g., thumb joint
    Interspinous Ligament
    Spinal ligament between adjacent vertebral spinous processes.
    Temporalis
    Muscle involved in closing the jaw.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Zygomaticus
    Muscle that raises the corners of the mouth.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Metatarsals (5 bones)
    5 bones forming the mid-foot.
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Achilles Tendon
    Tendon connecting the calf muscle to the heel bone.
    Vomer Bone
    Bone forming the nasal septum.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Tibia
    Shin bone, the larger bone in the lower leg.
    Ischium
    Part of the pelvis that supports weight while sitting.
    Sphenoid Bone
    Bone forming part of the base of the skull and sides of the orbits.
    Phalanges (14 bones)
    14 bones forming the toes.
    Clavicle
    Collarbone connecting the arm to the body.
    Cranial Bones
    Bones of the skull that protect the brain.
    Symphyses
    Cartilaginous joints where bones are connected by fibrocartilage.
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Sesamoid Bones
    e.g., patella, some found in hands/feet.

    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? The humerus is the largest bone in the arm.