Lecture 7 Brachium (Arm) Anatomy

The Brachium (Arm)

• The brachium, also known as the arm, is the upper limb region between the shoulder and the elbow, containing the humerus.
• Divided into anterior and posterior compartments by medial and lateral muscular septa, which are bands of connective tissue thicker than typical epimysium.
• Both septa provide transit for vessels and nerves traveling between the axilla and antebrachium.
• The neurovascular compartment is located medially, housing a large collection of vessels and nerves embedded in loose areolar and adipose tissue, protecting them from the humerus.

Anterior Compartment

• Located anterior to the humerus and contains muscles responsible for flexing the shoulder and elbow joints.
• All muscles in this compartment are innervated by the musculocutaneous nerve.
• Muscles include: coracobrachialis, biceps brachii, and brachialis.

Coracobrachialis

• A fusiform muscle, running from the coracoid process to the medial shaft of the humerus, that flexes and adducts the shoulder.
• Stabilizes the shoulder joint by resisting inferior displacement of the humerus (gravity, carried load).

Biceps Brachii

• A fusiform muscle with two heads converging on a single insertion point.
• The long head runs through the intertubercular groove, attaching to the supraglenoid tubercle of the scapula; its tendon is surrounded by a synovial sheath to reduce friction.
• A ruptured biceps tendon (usually the long head) is caused by tearing of the tendon due to excessive wear; unopposed muscle bunches up in the anterior compartment, resulting in "Popeye's deformity" with minimal loss of function due to the short head's action.
• Surgical repair of a ruptured biceps tendon in young and athletic individuals involves reattaching the long head to the proximal shaft of the humerus.
• The short head originates directly from the coracoid process.
• A thick, round tendon inserts on the radial tuberosity with the bicipital aponeurosis being a broad, flat portion that curves medially and is continuous with the antebrachial fascia protecting deep neurovascular structures.
• A three joint muscle, flexing the shoulder and elbow joints and strongly supinating the superior radioulnar joint.

Brachialis

• A fusiform muscle originating from the anterior shaft of the humerus.
• It crosses anterior to the elbow joint and inserts on the proximal portion of the anterior ulna.
• The prime elbow flexor, working strongly at all joint angles

Posterior Compartment

• This muscular compartment is located posterior to the humerus.
• Muscles in this compartment are responsible for extending the shoulder and elbow, and are innervated by the radial nerve.
• Includes the triceps brachii and anconeus muscles.

Triceps Brachii

• A fusiform muscle with three heads converging on a single insertion point.
• The long head originates off the infraglenoid tubercle, extending the shoulder and elbow while stabilizing the shoulder joint by resisting inferior displacement of humerus (gravity, carried load).
• The lateral head originates off the proximal posterior shaft of the humerus and is the strongest elbow extensor.
• The medial head originates off the distal posterior shaft of the humerus (deep to the long head) and is the most active elbow extensor.

Anconeus

• Runs medially from the lateral epicondyle to the olecranon.
• An accessory extensor that tenses the joint capsule to prevent pinching.

Cubital Fossa

• A depression on the anterior elbow containing variable amounts of fat and neurovascular structures.
• It’s a triangular space bordered by an imaginary line connecting the epicondyles, the lateral border of the pronator teres, and the medial border of the brachioradialis.
• The median cubital vein, connecting the basilic and cephalic veins, is found in the subcutaneous tissue here.
• The median cubital vein is a common site for blood draws due to its superficial location and ease of access.

Brachial Artery

• The main artery of the brachium and a continuation of the axillary artery past the inferior border of the teres major.
• Runs in the neurovascular compartment with veins, nerves, and lymphatics.
• It starts medially, crosses anterior to the coracobrachialis, then travels posterior to the medial border of the biceps brachii to the cubital fossa.
• Terminates at the cubital fossa, splitting into radial and ulnar arteries.
• Numerous branches are given off, including unnamed muscular branches.
• Several branches anastomose (merge) with inferior branches in the forearm, forming collateral circulation for rerouting blood flow if the brachial artery is compressed (e.g. in elbow flexion).

Profunda Brachii (Deep Artery of the Arm)

• Branches off the brachial artery just past teres major and runs with the radial nerve through the spiral groove in the posterior compartment.
• It provides vascular supply for the posterior compartment.
• It divides at a variable level along shaft into the radial collateral branch (anterior to epicondyle, anastomoses with recurrent radial artery) and the middle collateral branch (posterior to epicondyle, anastomoses with recurrent interosseus artery).

Humeral Nutrient Artery

• A small branch just distal to the coracobrachialis.
• Penetrates the nutrient foramen of the humerus to supply bone tissue.

Superior Ulnar Collateral Artery

• Branches mid-brachium to run with the ulnar nerve.
• Runs posterior to the medial epicondyle and anastomoses with the posterior ulnar recurrent artery.

Inferior Ulnar Collateral Artery

• Branches just proximal to the medial epicondyle.
• Crosses the elbow joint anterior to the medial epicondyle and anastomoses with the anterior ulnar recurrent artery.

Veins of the Brachium

• More numerous and complex than the arteries.
• Typically follow the same path and share names with corresponding arteries.

Brachial Vein

• Accompanies the brachial artery, draining blood into the axillary vein.
• Observed as venae comitantes, typically two paired vessels on either side of the artery.
• The arrangement is common in the appendages, and the veins commonly exist with complex branching.

Basilic Vein

• A subcutaneous vessel on the medial aspect of the arm.
• Dives through the fascia of the brachium to fuse with the brachial vein, forming the axillary vein.

Cephalic Vein

• A subcutaneous vessel on the lateral aspect of the arm.
• Runs superiorly in the deltopectoral groove and pierces the clavipectoral fascia to drain into the axillary vein.

Nerves of the Brachium

• Four terminal branches from the brachial plexus pass through the arm, but only two innervate brachial structures.
• Additional cutaneous branches also pass through the brachium.
• Nerves include: musculocutaneous, radial, median, and ulnar.

Musculocutaneous Nerve

• A terminal branch from the brachial plexus.
• Pierces the coracobrachialis to enter the anterior compartment.
• Provides innervation to the biceps brachii, brachialis, and coracobrachialis.

Radial Nerve

• A terminal branch from the brachial plexus.
• Can be viewed in the triangular interval between the long and lateral heads of the triceps brachii.
• Travels along the spiral groove, piercing the lateral muscular septum to emerge anterior to the lateral epicondyle and continue into the forearm.
• Gives off extensive branches to the triceps brachii in the posterior compartment.
• Provides numerous cutaneous branches to the skin along the back of the arm.

Median Nerve

• Travels in the neurovascular compartment with the brachial artery/vein.
• Passes with the brachial artery in the middle of the cubital fossa.
• No direct innervation in the brachium; it continues to the antebrachium to innervate the anterior compartment and hand.

Ulnar Nerve

• Travels in the neurovascular compartment posterior to the brachial artery/vein and median nerve.
• Passes posterior to the medial epicondyle to enter the antebrachium.
• Sits in a wedge-shaped depression between the epicondyle and olecranon; perturbation can cause transient paresthesia ("pins and needles"); commonly referred to as the "funny bone".
• No direct innervation in the brachium; it continues to the antebrachium to innervate the anterior compartment and hand.

Overview of the brachium, the upper limb region between the shoulder and elbow. Includes the anterior compartment and muscles such as the coracobrachialis and biceps brachii. Covers neurovascular components and muscle functions.