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These three muscles act as flexors at the elbow joint. [5] The extensor carpi radialis brevis and longus are both weak flexors at the elbow joint. Brevis moves the arm from ulnar abduction to its mid-position and flexes dorsally. Longus is a weak pronator in the flexed arm and a supinator in the outstretched arm.
The intrinsic muscles of the forearm act on the forearm, meaning, across the elbow joint and the proximal and distal radioulnar joints (resulting in pronation or supination), whereas the extrinsic muscles act upon the hand and wrist. In most cases, the extrinsic anterior muscles are flexors, while the extrinsic posterior muscles are extensors.
The median nerve enters the forearm between the two heads of the muscle, and is separated from the ulnar artery by the ulnar head. The muscle passes obliquely across the forearm, and ends in a flat tendon, which is inserted into a rough impression at the middle of the lateral surface of the body of the radius , just distal to the insertion of ...
This nerve continues in the arm, travelling in a plane between the biceps and triceps muscles. At the cubital fossa, this nerve is deep to the pronator teres muscle and is the most medial structure in the fossa. The nerve passes into the forearm. The ulnar nerve, origin C8-T1, is a continuation of the medial cord of the brachial plexus.
Despite the bulk of the muscle body being visible from the anterior aspect of the forearm, the brachioradialis is a posterior compartment muscle and consequently is innervated by the radial nerve. [5] Of the muscles that receive innervation from the radial nerve, it is one of only four that receive input directly from the radial nerve.
There are generally twelve muscles in the posterior compartment of the forearm, which can be further divided into superficial, intermediate, and deep. Most of the muscles in the superficial and the intermediate layers share a common origin which is the outer part of the elbow, the lateral epicondyle of humerus.
The lateral intermuscular septum extends from the lower part of the crest of the greater tubercle of the humerus, along the lateral supracondylar ridge, to the lateral epicondyle; it is blended with the tendon of the deltoid muscle, gives attachment to the triceps brachii behind, and to the brachialis, brachioradialis, and extensor carpi radialis longus muscles in front.
On a person's distal forearm, just before the wrist, there are either two or three tendons. The tendon of the flexor carpi ulnaris is the most medial (closest to the little finger) of these. The most lateral one is the tendon of flexor carpi radialis muscle, and the middle one, not always present, is the tendon of palmaris longus.