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    Related Topics

    From Musculoskeletal System

    Femur
    Thigh bone, the longest and strongest bone in the body.
    Fibula
    Smaller bone in the lower leg, located alongside the tibia.
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Metacarpals (5 bones)
    5 bones forming the palm of the hand.
    Brachioradialis
    Muscle responsible for forearm flexion.
    Ethmoid Bone
    Bone forming part of the nasal cavity and the orbit.
    Sphenoid Bone
    Bone forming part of the base of the skull and sides of the orbits.
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Sacrum
    Triangular bone at the base of the spine.
    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.
    Acromioclavicular Joint
    The acromioclavicular joint connects the clavicle and scapula at the top of the shoulder, enabling smooth scapular motion and stability during arm movements.
    Pubis
    Part of the pelvis that joins with the opposite side to form the pubic symphysis.
    Palatine Bones
    Bones forming part of the hard palate and nasal cavity.
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Tibialis Anterior
    Muscle that dorsiflexes and inverts the foot.
    Posterior Longitudinal Ligament
    Spinal ligament running along the back of the vertebral column.
    Symphyses
    Cartilaginous joints where bones are connected by fibrocartilage.
    Triceps Brachii
    Muscle responsible for elbow extension.
    Coccygeus
    Pelvic floor muscle supporting the coccyx.
    Ball-and-Socket Joints
    e.g., shoulder, hip
    Rectus Abdominis
    Abs muscle that flexes the trunk.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Flexor and Extensor Groups
    Muscles responsible for flexing and extending the hand and wrist.
    Temporal Bones
    Bones forming the lower sides of the skull and housing the ears.

    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 sacrum is the foundation of the spine and the pelvis.