The muscles in your forearm are arranged in two compartments, the anterior and posterior. Flexor muscles are more massive than extensor muscles, and are antigravity muscles. There are 8 flexor muscles in the anterior compartment, five of them superficial. Extensor muscles are arranged in deep and superficial groups. The radial nerve supplies both the extensors and flexors.
The muscles of the forearm control both fine and gross hand and finger movements. They are divided into two compartments based on their anatomical structure and functional role. The posterior group is involved in pronation of the hand and wrist while the anterior group controls finger flexion. The anterior group also acts on the proximal radioulnar joint. These muscles are very important for controlling the pronation of the forearm.
The muscles of the forearm, or the posterior compartment, act on the wrist and elbow. They are divided into three layers: superficial, intermediate, and deep. Each compartment contains one muscle, the extensor carpi ulnaris. The median nerve innervates the anterior compartment. The ulnar nerve innervates the deep layer. The radial nerve innervates the anterior compartment muscles.
The brachialis is a muscle located in the forearm that attaches to the humerus. The brachialis originates on the lower anterior surface of the humerus and inserts into the ulna near the coranoid process. It functions to move the insertion point during contraction. The brachialis muscle is a synergist with the biceps brachii.
Triceps injuries occur most often when the arm is hyperextended, or if the triceps muscle is stretched to an excessive degree. The tendon that attaches to the triceps muscle is also susceptible to injury. Though not commonly imaged, tendon injuries can occur distally or in the olecranon process. They often present as a complete tear, or a partial disruption of the tendon. A partial-thickness tendon tear is most often identified by hypoechoic swelling of the intact fibers. An incomplete disruption of the tendon is a sign of a partial tear, and hyperechoic shadowing suggestive of an avulsion fracture.
The supinator muscles of the forearm are primarily responsible for the flexion and extensor movements of the forearm. These muscles are innervated by the deep branch of the radial nerve that eventually becomes the posterior interosseous nerve. The roots of the supinator muscles are primarily located in the C6 and C5 vertebrae, but can also come from the C7. Generally, the supinator muscles are referred to as brachioradialis, supinator brevis, or supinator longus. However, the two muscles are often confused due to the different names.
The coracobrachialis is a group of muscles in the forearm and shoulder that can cause pain. The name of this group of muscles is derived from the location of their attachments on the body, specifically on the coracoid process of the scapula and the shaft of the humerus. The word “brachialis” derives from the Latin word brachium, which means “arm.”