Muscles of the Pectoral Region and Shoulder

Muscles of the Pectoral Region and Axilla

• Pectoralis major originates from the medial half of the clavicle and sternum; inserts on the humerus; innervated by lateral and medial pectoral nerves; responsible for flexing, adducting, and medially rotating the arm.
• Pectoralis minor originates from the third to fifth ribs; inserts on the coracoid process of the scapula; innervated by medial pectoral nerve; depresses the scapula and elevates the ribs.
• Subclavius arises from the junction of the first rib and its costal cartilage; attaches to the inferior surface of the clavicle; innervated by the nerve to subclavius.

Muscles of the Shoulder

• Deltoid muscle originates from the lateral third of the clavicle, acromion, and spine of the scapula; inserts at the deltoid tuberosity of the humerus; innervated by the axillary nerve; performs a variety of arm movements including abduction, adduction, flexion, extension, and rotation.
• Supraspinatus originates from the supraspinous fossa of the scapula; inserts on the greater tubercle of the humerus; innervated by suprascapular nerve; primarily abducts the arm.
• Infraspinatus originates from the infraspinous fossa; attaches to the middle facet of the greater tubercle of the humerus; innervated by suprascapular nerve; laterally rotates the arm.
• Subscapularis arises from the subscapular fossa; inserts on the lesser tubercle of the humerus; innervated by upper and lower subscapular nerves; adducts and medially rotates the arm.
• Teres major originates from the inferior angle of the scapula; inserts on the medial lip of the intertubercular groove of the humerus; innervated by lower subscapular nerve; adducts and medially rotates the arm.
• Teres minor originates from the lateral border of the scapula; inserts at the lower facet of the greater tubercle of the humerus; innervated by axillary nerve; performs lateral rotation of the arm.
• Latissimus dorsi originates from the spines of T7-T12, thoracolumbar fascia, iliac crest, and lower ribs; inserts at the floor of the bicipital groove of the humerus; innervated by the thoracodorsal nerve; adducts, extends, and medially rotates the arm.

Triangular Space and Interval

• The triangular space is located between the teres minor (superior), teres major (inferior), and the long head of the triceps (lateral); contains the circumflex scapular vessels.
• The triangular interval is formed by the teres major (superior), long head of triceps (medially), and medial head of triceps (laterally); contains the radial nerve and profunda brachii artery.

Muscles of the Arm

• Coracobrachialis originates from the coracoid process; inserts on the middle third of the medial surface of the humerus; innervated by the musculocutaneous nerve; flexes and adducts the arm.
• Biceps brachii has a long head from the supraglenoid tubercle and a short head from the coracoid process; inserts on the radial tuberosity; innervated by the musculocutaneous nerve; flexes the arm and forearm, and supinates the forearm.

Muscles of the Posterior Forearm

• Brachioradialis originates from the lateral supracondylar ridge of the humerus; inserts at the base of the radial styloid process; innervated by the radial nerve; flexes the forearm.
• Extensor muscles arise mainly from the lateral epicondyle and perform movements such as extending the wrist (Ext. carpi radialis longus and brevis) and fingers (Ext. digitorum, Ext. indicis, etc.) with radial nerve innervation.
• Supinator muscle originates from the lateral epicondyle and ulna; inserts on the radius; innervated by the radial nerve; supinates the forearm.

Interosseous Membrane

• A dense connective tissue sheet between the radius and ulna; its gap allows passage for posterior interosseous vessels.
• Serves as attachment for hand muscles; divides the forearm into anterior and posterior compartments.

Characteristics of the Arm and Forearm

• The carrying angle causes forearm deviation (5°-15°) laterally from a straight arm and is more pronounced in women; not visible when the forearm is flexed or pronated.
• Pronation and supination occur at proximal and distal radioulnar joints; biceps brachii primarily contributes to supination.

Muscles of the Hand

• Abductor pollicis brevis and Flexor pollicis brevis innervated by the median nerve; involved in thumb movements such as abduction and flexion.
• Adductor pollicis is innervated by the ulnar nerve; adducts the thumb.
• Lumbricals and interossei muscles (dorsal and palmar) assist in finger flexion and extension; innervated by median and ulnar nerves.

Clinical Correlates

• Carpal tunnel syndrome results from median nerve compression, causing pain, paresthesia, and potential thenar muscle atrophy; treated with bracing or surgical release.
• The palmar side of the hand experiences skin wrinkles due to the action of palmaris brevis, innervated by the ulnar nerve.

Test your knowledge on the anatomy of the pectoral region, axilla, and shoulder muscles. This quiz covers the origin, insertion, innervation, and functions of key muscles such as the pectoralis major, minor, deltoid, and others. Perfect for students studying human anatomy or related fields.