The arterial supply to the upper limb is a continuous pathway of blood flow. Anatomists use different names for this single vessel based on the region it traverses. The axillary artery and the brachial artery are sequential names for the same major blood vessel, distinguished purely for anatomical clarity and surgical reference. This naming convention allows medical professionals to precisely locate and discuss specific segments of the artery.
Defining the Axillary Artery’s Borders
The axillary artery begins as a continuation of the subclavian artery at the lateral border of the first rib. This marks the vessel’s entrance into the axilla, or armpit region. The artery is encased within the axillary sheath, a fibrous covering that also encloses the cords of the brachial plexus, the network of nerves that supplies the upper limb.
The artery’s path through the axilla is not straight and changes depending on arm position. It is flanked medially by the axillary vein for its entire length. The cords of the brachial plexus surround the artery, creating a close relationship with major nerves of the arm, including the median nerve.
The Anatomical Landmark for the Name Change
The transition from the axillary artery to the brachial artery is defined by a specific muscle boundary. The axillary artery officially becomes the brachial artery when it crosses the inferior border of the Teres Major muscle. This large shoulder muscle connects the scapula to the humerus and forms the lower boundary of the axilla.
The adoption of a new name at this point serves as a standardized reference for clinicians. It indicates that the artery has left the confines of the armpit and entered the upper arm. The inferior margin of the Teres Major muscle is a fixed landmark, preventing ambiguity when discussing injury location or surgical procedures.
At this boundary, the artery is closely associated with the median nerve. As the vessel passes this border, it is accompanied by the radial nerve and the profunda brachii artery, its first major branch in the new segment. The Teres Major muscle acts as a clear dividing line, marking the end of the axillary artery and the beginning of the brachial artery.
The Course of the Brachial Artery
Once the vessel transitions, the brachial artery becomes the main blood supply for the upper extremity. It travels down the anteromedial side of the arm, running along the humerus and lying deep to the Biceps Brachii muscle. Throughout its course, it remains close to the median nerve, which crosses over from the lateral to the medial side as they descend toward the elbow.
The brachial artery continues its path until it reaches the cubital fossa, the triangular depression on the anterior side of the elbow. Here, it is protected anteriorly by the bicipital aponeurosis. The artery’s journey ends in the cubital fossa, where it divides into its two terminal branches.
This bifurcation marks the end of the main trunk. The brachial artery splits into the radial artery, which runs down the thumb-side of the forearm, and the ulnar artery, which travels down the little-finger side. These two vessels continue the blood supply to the forearm, wrist, and hand.
Major Blood Vessel Offshoots in the Upper Limb
The main arterial trunk gives rise to several offshoots that supply the surrounding muscles and joints. A significant branch off the proximal brachial artery is the profunda brachii artery, or deep artery of the arm. This vessel travels with the radial nerve and supplies the posterior compartment of the arm, including the Triceps Brachii muscle.
The profunda brachii artery wraps around the humerus in the radial groove, supplying deep structures before contributing to a network around the elbow joint. Closer to the elbow, the brachial artery also gives off the superior ulnar collateral artery and the inferior ulnar collateral artery. These two vessels travel toward the medial side of the elbow joint.
All these branches contribute to an elaborate network of connected blood vessels called an anastomosis, particularly around the shoulder and elbow. This system of collateral circulation is a biological safeguard. It ensures that blood can still reach the forearm and hand even if the main brachial artery is temporarily compressed or blocked.