Although we use the words ‘arm’ or ‘hand’ loosely in everyday language to mean the whole of the upper limb, these words have very specific meanings in anatomy. Arm means only the part of the upper extremity between the shoulder and elbow joints and ‘hand’ implies the parts beyond the wrist, the palms and fingers.
Arm anatomy, therefore, includes all the structures located between the shoulder and elbow joints. Find out how the arm is divided into compartments, what its contents are and get concise descriptions of the anatomy of arm muscles, the arm bone, arm nerves and veins of the arm.
The arm has intermuscular septa, which are extensions of the deep fasica in between the muscles. These septa divide the arm into compartments and allow the muscles to freely slide over each other when they contract. The lower half of the arm is divided by these septa into anterior (front) and posterior (back) compartments.
Humerus – the Arm Bone
The humerus is the bone in the arm region, the largest of the bones of the upper limb. It is a long bone located in the centre of the arm, completely surrounded by muscles. Its parts are a head, neck, body and a lower end.
The head of the humerus is shaped like a hemisphere that fits into the shallow glenoid cavity of the scapula (the shoulder blade) to form the shoulder joint. The body is a long and sturdy shaft that gives attachment to some of the muscles of the arm. The lower end bears prominent bony projections called epicondyles on either side. The lower end connects with the radius and the ulna, bones of the forearm, to form the elbow joint.
Anatomy of Arm Muscles
While the upper part of the arm is wrapped by some of the shoulder muscles like the deltoid, the muscles that actually occupy the arm are:
- biceps brachii
- coracobrachialis
- brachialis
- triceps brachii
The first three muscles occupy the front of the arm while the triceps forms the bulk of the back of the arm. While the biceps and coracobrachialis cause flexion at the shoulder joint, the triceps cause extension at the elbow. Read all about arm muscle anatomy for details about the origin and insertion, nerve supply and actions of each of these muscles.
Anatomy of Arm Nerves
The entire upper limb is supplied by nerves arising from the brachial plexus, a major nerve network formed by the cervical and first thoracic spinal nerves. Many important nerves run through the arm, some of them to supply the structures of the arm and others on their way to the forearm and hand. The nerves present in the arm are:
- radial nerve
- median nerve
- ulnar nerve
- musculocutaneous nerve
The musculocutaneous nerve comes from the lateral cord of the brachial plexus. After supplying the biceps, coracobrachialis and brachialis muscles of the arm, it ends up as the lateral cutaneous nerve of the forearm, the nerve for sensation of part of the forearm skin. The radial nerve arises from the posterior cord of the brachial plexus and supplies the triceps muscle in the arm before heading towards the hand.
The ulnar nerve only passes through the arm and does not control any structure here. The median nerve, too, mainly supplies the muscles in the palm and fingers, but gives off branches to the arteries in the arm.
Read brachial plexus anatomy for complete details about how this nerve network is formed and what nerves arise from it.
Anatomy of Arm Veins and Arteries
The major blood vessel in the arm is the brachial artery. This vessel is a continuation of the axillary artery and carries nutrition to all the structures in the arm through its branches. You can feel its pulsation in front of the elbow just beside the biceps tendon. In fact, it is the pulsation of this artery that is used while measuring blood pressure with a sphygmomanometer and this is why the nurse places the stethoscope on the front of the elbow.
The branches of the brachial artery in the arm are:
- profunda brachii – that runs along with the radial nerve
- ulnar collateral artery – there are 2, the superior and inferior, supplying the arm muscles
- nutrient artery to the humerus – supplying the arm bone
There are veins accompanying every artery, for example, the brachial artery and the brachial vein, but the arrangement of veins can vary widely. The main veins in the arm are:
- basilic vein
- cephalic vein
The basilic vein runs along the inner side while the cephalic vein is located along the outer edge, especially at the front of the elbow. The two veins are often connected by the median cubital vein in front of the elbow. Both these veins, along with the brachial vein, empty into the axillary vein.
Arm anatomy is an important part of upper limb anatomy and includes the arm bone humerus, arm muscles, nerves of the arm, veins and arteries. Also read upper limb and hand bones for more about the upper limb skeleton.
Sources
Romanes, G.J. “Cunningham’s Manual of Practical Anatomy” (Oxord University Press; 15th Edition, 2003)
Lakshmi Ananth - Lakshmi Ananth is a practising ENT, head and neck surgeon and has faculty position at a medical college. She is specially interested in ...
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