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    From Musculoskeletal System

    Hinge Joints
    e.g., elbow, knee
    Nasal Bones
    Bones forming the bridge of the nose.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Diaphragm
    Primary muscle for breathing.
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Vertebral Column
    Spinal column consisting of vertebrae.
    Brachioradialis
    Muscle responsible for forearm flexion.
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Cervical Vertebrae (C1 - C7)
    Vertebrae in the neck region (C1-C7).
    Anterior Scalene Muscle
    The anterior scalene muscle is a deep neck muscle that elevates the first rib during inspiration and aids in neck flexion and stability, located between key neurovascular structures.
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Parietal Bones
    Bones forming the sides and roof of the skull.
    Abductor Digiti Minimi Muscle
    The abductor digiti minimi muscle is a hypothenar muscle that abducts and flexes the little finger, aiding grip and precision in hand movements.
    Ilium
    Uppermost and largest part of the hip bone.
    Gomphoses
    Fibrous joints where a peg fits into a socket (e.g., teeth in jaw).
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Clavicle
    Collarbone connecting the arm to the body.
    Gluteus Maximus
    Largest muscle in the buttocks responsible for hip extension.
    Temporal Bones
    Bones forming the lower sides of the skull and housing the ears.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Radius
    Forearm bone on the thumb side.
    Skull
    Bony structure of the head that encases the brain.

    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? Tendons attach muscles to bones.