Arm Anatomy: Muscles and Compartments

• The lecture aims to explain the anatomy of the arm, covering muscles, blood vessels, and nerves.
• The arm region is the part of the upper limb located between the shoulder and elbow joints.

Compartments of the Arm

• The deep fascia of the arm is known as the brachial fascia.
• The brachial fascia sends out two strong intermuscular septa: medial and lateral.
• Along with the humerus, these septa divide the arm into two compartments: anterior and posterior.
• The anterior compartment is the flexor compartment.
• The posterior compartment is the extensor compartment.

Muscles of the Arm

• Anterior compartment muscles: Biceps brachii, Coracobrachialis, and Brachialis.
• Posterior compartment muscle: Triceps brachii.
• Muscle study should include origin, insertion, nerve supply, and action.

Biceps Brachii Muscle

• The biceps brachii has two heads: a long head and a short head.

Biceps Brachii Muscle Origin

• Short head originates from the apex of the coracoid process.
• Long head originates from the supraglenoid tubercle.

Biceps Brachii Muscle Insertion

• Inserts on the radial tuberosity.

Biceps Brachii Muscle Features

• The tendon of the long head passes through the shoulder joint, superior to the head of the humerus.
• The tendon of the long head runs through the bicipital groove.
• The bicipital aponeurosis is a flat sheet of connective tissue that extends from the medial side of the biceps tendon, fusing with the deep fascia of the forearm.

Biceps Brachii Muscle Innervation

• The musculocutaneous nerve provides nerve supply.

Biceps Brachii Muscle Action

• The biceps brachii is a powerful supinator of the forearm.
• The biceps brachii is a powerful flexor of the forearm at the elbow joint.

Coracobrachialis Muscle

• The origin is the apex of the coracoid process.
• It inserts on the medial side of the mid-shaft of the humerus.

Coracobrachialis Muscle Innervation

• The musculocutaneous nerve penetrates the coracobrachialis muscle.

Coracobrachialis Muscle Action

• Flexes the arm at the shoulder joint.

Brachialis Muscle

• The brachialis muscle lies deep to the biceps muscle.
• Originates from the anterior aspect of the humerus (medial and lateral surfaces) and the intermuscular septa.
• Inserts on the ulnar tuberosity.

Brachialis Muscle Innervation

• Supplied by the musculocutaneous nerve.
• The lateral part is innervated by the radial nerve.

Brachialis Muscle Action

• The brachialis is a powerful flexor of the forearm at the elbow joint.

Triceps Muscle

• Only muscle in the posterior compartment.
• The triceps has three heads: long, medial, and lateral.

Triceps Muscle Origin

• Long head originates from the infraglenoid tubercle.
• Medial head originates from the posterior surface of the humerus (inferior to the radial groove).
• Lateral head originates from the posterior surface of the humerus (superior to the radial groove).

Triceps Muscle Insertion

• Inserts on the superior surface of the olecranon process of the ulna.

Triceps Muscle Innervation

• The triceps is supplied by the radial nerve.

Triceps Muscle Action

• Extension of the forearm at the elbow joint.

Intermuscular Spaces

• Quadrangular space contains the axillary nerve and posterior circumflex humeral artery and vein.
• Triangular space (Upper) contains the circumflex scapular artery.
• Triangular interval (Lower) contains the radial nerve and profunda brachii artery.

Brachial Artery

• The major artery of the arm, located in the anterior compartment.
• The brachial artery is palpable along its length.

Brachial Artery Origin

• The brachial artery is a continuation of the axillary artery at the lower border of the teres major.

Brachial Artery Termination

• The brachial artery terminates just distal to the elbow joint, dividing into radial and ulnar arteries.

Brachial Artery Course

• In the proximal arm, it lies on the medial side.
• In the distal arm, it runs midway between the medial and lateral epicondyles of the humerus.
• The brachial artery crosses anterior to the elbow joint in the cubital fossa.

Brachial Artery Branches

• Profunda brachii artery, nutrient artery, superior ulnar collateral artery, inferior ulnar collateral artery, radial artery, and ulnar artery.

Profunda Brachii Artery

• Largest branch of the brachial artery.
• It passes through the triangular interval to the posterior compartment with the radial nerve.
• The profunda brachii artery with the radial nerve pass along the radial groove, deep to the lateral head of the triceps muscle.
• The profunda brachii artery supplies the adjacent muscles.
• The profunda brachii artery gives off branches to anastomose with the posterior circumflex humeral artery and shares in the anastomosis around the elbow.

Brachial Veins

• Two veins pass along the medial and lateral sides of the brachial artery.
• They join the basilic vein or the axillary vein.