Arm Muscles and Nerve – Anatomy, Nerve Supply, Functions

Arm Muscles and Nerve /Brachium is a Latin word meaning the upper arm. This part of the upper limb contains powerful muscles that carry a considerable portion of the upper limb function. Also, vital peripheral nerves pass through the upper limb, namely the brachial plexus neurons. The brachial artery is the single most important blood vessel that gives branches to supply the whole upper limb. Because of the previously mentioned valuable structures, injury to the upper arm can cause severe problems in the entire upper limb.[rx]

Structure of Arm Muscles and Nerve

The upper limb can be divided anatomically into the shoulder, arm, elbow, forearm, wrist, and hand, respectively. The hand muscles can also divide into two compartments separated by two fascial septa, one on the medial side and the other on the lateral side. Muscles of the anterior fascial compartment contain biceps brachii, coracobrachialis, brachialis. The muscle of the posterior fascial compartment contains the three head of the triceps muscle.[rx]

The subdivision into compartments and fascial planes, in reality, is a didactic approach, as we know that in vivo, the muscular, vasculonervous, and purely connective structures are a continuum.

Blood Supply of Arm Muscles and Nerve

Blood Supply

The brachial artery is the main arterial supply to the arm. It starts from the lower border of teres major muscle as a continuation of the axillary artery, and it ends opposite to the neck of the radius by dividing it to ulnar and radial arteries. The brachial artery branches are the nutrient branch to the humerus, the profunda artery and ulnar collateral arteries that supply the posterior fascial compartment.[rx] The venous return of the arm is guaranteed in particular by the cephalic, basilica, and brachial veins.

Lymphatics

The superficial lymphatic vessels drain the superficial tissue upward to the axilla, those from the lateral side of the arm follow the cephalic vein to the infraclavicular nodes; those from the medial side the arm follow basilic vein to the lateral group of axillary nodes. Whereas the deep lymphatic vessels drain the muscles and deeper structures to the lateral group of axillary nodes.[rx]

Nerves of Arm Muscles and Nerve

Most of the brachial plexus branches pass through the arm; the following nerves pass through the upper arm[4][5]:

Musculocutaneous nerve: which innervates the biceps, coracobrachialis, and brachialis muscles. Plus, it gives a sensory branch to the lateral forearm and articular branch to the elbow. Its origin is the lateral cord of the brachial plexus (C5,6,7). The nerve runs downward and laterally piercing the coracobrachialis muscle then runs between the biceps and brachialis muscles. It terminates as the lateral cutaneous nerve of the forearm.

Median nerve: originates from the medial and lateral cord of the brachial plexus. It runs downward and lateral to the brachial artery in the upper arm halfway its course crosses the artery to reside on its medial side. The median nerve gives no branches to the arm except for small vasomotor branches to the brachial artery.

Ulnar nerve: this nerve gives no branches in the arm, mainly innervates the hand. The origin of the ulnar nerve is from the eighth cervical and first thoracic roots of the brachial plexus. The ulnar nerve runs downward at the medial side of the brachial artery. At the level of the insertion of the coracobrachialis, it pierces the medial fascial septum to enter the posterior compartment then the nerve runs posteriorly to the medial epicondyle of the humerus.

Radial nerve: originates from the posterior cord of the brachial plexus. The nerve rotates around the humerus in the spinal groove accompanied by the profunda artery, and it lies directly in contact with the humerus shaft. It goes through the lateral fascial septum downward and in front of the cubital fossa between the brachialis and brachioradialis. It gives cutaneous branches as the posterior cutaneous nerve of the arm, inferior lateral cutaneous nerve of the arm and posterior cutaneous nerve of the forearm. And muscular branches to triceps brachii, anconeus, brachioradialis, and extensor carpi radialis longus.

Muscles of Arm Muscles and Nerve

The anterior compartment of the arm contains (biceps brachii, coracobrachialis, brachialis)[rx]:

The biceps brachii: the long head originates from the supraglenoid tubercle of the scapula, and the short head originates from the tip of the coracoid process of the scapula. The insertion of this muscle will be on the posterior part of the radius tuberosity and by the bicipital aponeurosis to the medial aspect of the forearm. It serves as a powerful supinator of the forearm and flexion of the elbow joint and plays a minimal role in flexion of the shoulder. Innervated by the musculocutaneous nerve.

The coracobrachialis: the name of the muscle explains it very well; it starts from the coracoid process and inserts into the middle of the medial side of the humerus. It flexes the arm and serves as a weak adductor. The musculocutaneous nerve innervates it.

The brachialis: it started from the front of the lower half of the humerus and inserted in the anterior aspect of the coronoid process of the ulna. It is a strong elbow flexor. Innervated by musculocutaneous nerve and a small part of the muscle by the radial nerve.[rx]

The posterior fascial compartment contains ( three heads of the triceps muscle)[rx]:

The triceps muscle: long head from infraglenoid tubercle, the lateral head from the upper half of the posterior surface of humerus shaft above the spiral grove, and the medial from the lower half of the shaft of the humerus at the posterior surface below the spiral grove. They all inserted into the ulna olecranon as a common tendon. The action of this muscle is the extension of the elbow joint and supplied by the radial nerve.