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    From Musculoskeletal System

    Pivot Joints
    e.g., atlanto-axial joint
    Hinge Joints
    e.g., elbow, knee
    Synchondroses
    Cartilaginous joints where bones are connected by hyaline cartilage.
    Pelvic Floor Muscles
    Muscles that support pelvic organs.
    Acromioclavicular Ligament
    Ligament that connects the acromion to the clavicle.
    Adductors
    Muscles that bring the thighs toward the midline.
    Occipital Bone
    Bone forming the back and base of the skull.
    Obliques (External and Internal)
    Muscles responsible for torso rotation.
    Lumbar Vertebrae (L1 - L5)
    Vertebrae in the lower back (L1-L5).
    Radius
    Forearm bone on the thumb side.
    Sacrum
    Triangular bone at the base of the spine.
    Patella
    Knee cap, protecting the knee joint.
    Quadriceps Tendon
    Tendon that connects the quadriceps to the patella.
    Coracoacromial Ligament
    Ligament that connects the acromion to the coracoid process.
    Latissimus Dorsi
    Back muscle responsible for arm adduction and extension.
    Masseter
    Muscle that elevates the mandible.
    Glenohumeral Ligaments
    Shoulder ligaments that stabilize the shoulder joint.
    Extensor Tendons
    Tendons that help extend the fingers and toes.
    Posterior Longitudinal Ligament
    Spinal ligament running along the back of the vertebral column.
    Zygomaticus
    Muscle that raises the corners of the mouth.
    Deltoid
    Shoulder muscle responsible for arm abduction.
    Achilles Tendon
    Tendon connecting the calf muscle to the heel bone.
    Vertebral Column
    Spinal column consisting of vertebrae.
    Nasal Bones
    Bones forming the bridge of the nose.
    Ligamentum Flavum
    Spinal ligament connecting the laminae of adjacent vertebrae.

    Pectoralis Major

    Reviewed by our medical team

    Chest muscle responsible for shoulder movement.

    1. Overview

    The pectoralis major is a large, fan-shaped, superficial muscle located on the anterior chest wall. It is one of the most powerful muscles of the upper body and plays a primary role in movements of the shoulder joint, particularly adduction and medial rotation of the humerus. It contributes to the contour of the chest and is significant in both functional movement and aesthetic musculature.

    2. Location

    The pectoralis major is found on the anterior thoracic wall:

    • Medially: Originates from the sternum and the medial portion of the clavicle.

    • Laterally: Inserts into the upper humerus (intertubercular sulcus).

    • Superficial to: The pectoralis minor and the upper ribs.

    • Forms: The anterior wall of the axilla (armpit).

    3. Structure

    The pectoralis major is a thick, triangular muscle composed of two heads:

    • Clavicular head: Originates from the medial half of the clavicle.

    • Sternocostal head: Originates from the anterior surface of the sternum, costal cartilages of ribs 1–6 (or 1–7), and the aponeurosis of the external oblique muscle.

    • Insertion: Both heads converge to insert on the lateral lip of the intertubercular groove (bicipital groove) of the humerus.

    • Innervation: Lateral and medial pectoral nerves (C5–T1).

    • Blood supply: Primarily from the thoracoacromial artery and lateral thoracic artery.

    4. Function

    The pectoralis major has several primary functions involving the upper limb:

    • Adduction of the humerus: Brings the arm toward the midline of the body.

    • Medial (internal) rotation: Rotates the humerus inward.

    • Flexion of the humerus: Especially by the clavicular head; assists in lifting the arm forward.

    • Extension of the flexed humerus: The sternocostal head helps bring the arm back to the anatomical position from a flexed position.

    5. Physiological role(s)

    Beyond basic movement, the pectoralis major supports several functional processes:

    • Assists in respiration: Can act as an accessory muscle of inspiration when the arms are fixed, helping expand the thoracic cage.

    • Stabilizes the shoulder joint: Works with surrounding musculature to hold the humeral head in place.

    • Contributes to posture: Influences scapular and thoracic positioning during static and dynamic activity.

    • Enables pushing strength: Essential for activities like pushing open a door, performing push-ups, or throwing.

    6. Clinical Significance

    The pectoralis major can be involved in a variety of medical and athletic conditions:

    • Muscle tear or rupture:

      • Most commonly occurs in weightlifters during eccentric loading (e.g., bench press).

      • Presents with pain, bruising, weakness in arm adduction, and visible deformity of the chest wall.

      • Complete ruptures often require surgical repair.

    • Poland syndrome:

      • A congenital condition involving underdevelopment or absence of the pectoralis major (usually unilateral), often with ipsilateral hand abnormalities.

    • Pectoral muscle tightness:

      • Shortening of the muscle from poor posture or overuse can lead to shoulder protraction and upper-crossed syndrome.

    • Electromyography (EMG) testing:

      • Used to assess nerve conduction and muscle activity in cases of brachial plexus injuries or thoracic outlet syndrome.

    • Surgical reconstruction:

      • May be used as a flap in reconstructive surgeries (e.g., pectoralis major flap in head and neck surgery).

    Did you know? The sternocleidomastoid muscle helps rotate the head.