The (upper) arm muscles are a group of five muscles located in the region between the shoulder and elbow joints. They are divided into two distinct compartments of the arm. The anterior (flexor) compartment contains the biceps brachii, coracobrachialis and brachialis muscles. The posterior (extensor) compartment contains mainly the triceps brachii muscle. Even though the anconeus muscle is not anatomically located in the arm region, it is often considered to be a part of this muscle group. This is mainly due to the fact that its function is closely related to the triceps brachii muscle.
The prime function of the muscles in the anterior compartment is flexion of the forearm at the elbow joint and adduction of the arm at the shoulder joint. Additional actions of these muscles include flexion of the arm at the shoulder joint and forearm supination. The triceps brachii muscle is the prime extensor of the forearm at the elbow joint, with assistance from the anconeus muscle, but is also capable of weak arm extension and adduction. The muscles in the flexor compartment are mainly innervated by the musculocutaneous nerve, while the extensors are innervated by the radial nerve.
This article will introduce you to the anatomy and function of the arm muscles.
|Definition and function||Group of muscles located around the humerus in the upper limb, which primarily flex and extend the forearm|
|Muscles||Biceps brachii, coracobrachialis, brachialis, triceps brachii and anconeus|
|Innervation||Flexors: musculocutaneous nerve, radial nerve (brachialis only)
Extensors: radial nerve
Biceps brachii is one of the three muscles found in the anterior compartment of the arm. It gets its name from its two heads, each of which has a separate origin. The long head originates from the supraglenoid tubercle of scapula, while the short head shares its origin with the coracobrachialis muscle at the coracoid process of scapula.
The muscle fibers from both heads converge to a single tendon that inserts on the radial tuberosity of radius. It is innervated by the musculocutaneous nerve (C5-C6) and receives its blood supply from the brachial artery. Its actions include strong flexion and supination of the forearm, as well as week flexion of the arm at the shoulder joint. Additionally, the long head of the biceps has an important stabilizing role on the shoulder joint.
Coracobrachialis is the most medial muscle in the anterior compartment of the arm. Its attachments at the coracoid process of the scapula and the anterior surface of the shaft of humerus make coracobrachialis a strong adductor of the arm. Additionally, this muscle is also a weak flexor of the arm at the shoulder joint.
It receives its innervation from the musculocutaneous nerve (C5-C6), while its blood supply comes from the muscular branches of the brachial artery.
Brachialis is the last of the three muscles forming the anterior compartment of the arm. It originates from the distal half of the anterior surface of the humerus and inserts into the coronoid process and the tuberosity of ulna.
Brachialis receives innervation from the musculocutaneous (C5,C6) and radial nerves (C7) and its vascular supply from the brachial, radial recurrent arteries and branches of the inferior ulnar collateral arteries. Brachialis is the main flexor of the forearm at the elbow joint.
Triceps brachii is a large muscle found in the posterior (extensor) compartment of the arm. It consists of three distinct muscle bellies (heads) each of which has a different origin but share the same insertion point. The long head arises from the infraglenoid tubercle of scapula, the medial head from the posterior surface of the humerus (inferior to radial groove), while the lateral head originates from the posterior surface of the humerus (superior to radial groove). All three heads join to form a single tendon, which inserts onto the olecranon of ulna and fascia of the forearm.
Triceps brachii is innervated by the radial nerve (C6-C8) and receives its blood supply from the deep brachial and superior ulnar collateral arteries. Triceps brachii is the prime extensor of the forearm at the elbow joint. Additionally, due to its attachment on the scapula, it can also act as a weak extensor and adductor of the arm at the shoulder joint.
Feeling like all these muscles are a bit much for you? Learn the attachments, innervations and functions of the arm muscles faster and easier with our upper extremity muscle charts!
Anconeus is a small muscle located at the posterior aspect of the elbow. It stretches between the lateral epicondyle of humerus and the lateral surface of the olecranon of ulna. It assists the triceps brachii in elbow extension and stabilizes the elbow joint. Its innervation comes from the radial nerve (C7-C8) and blood supply from the posterior interosseous recurrent artery.
To further your learning on the anconeus and arm arm anatomy in general check out the following article and study units.
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