Brachialis muscle
| Brachialis | |
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| Deep muscles of the chest and front of the arm, with the boundaries of the axilla. (Brachialis visible at bottom right.) | |
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| Cross-section through the middle of upper arm. (Brachialis labeled at center left.) | |
| Latin | musculus brachialis |
| Gray's | subject #124 444 |
| Origin | anterior surface of the humerus, particularly the distal half of this bone |
| Insertion | coronoid process and the tuberosity of the ulna |
| Artery | radial recurrent artery |
| Nerve | musculocutaneous nerve (C5, C6) |
| Actions | flexion at elbow joint |
The brachialis (brachialis anticus) is a muscle in the upper arm that flexes the elbow joint. It lies deeper than the biceps brachii, and is a synergist that assists the biceps brachii in flexing at the elbow. It makes up part of the floor of the region known as the cubital fossa.
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[edit] Origin and insertion
The brachialis originates from the lower half of the front of the humerus, near the insertion of the deltoid muscle, which it embraces by two angular processes. Its origin extends below to within 2.5 cm of the margin of the articular surface of the humerus at the elbow joint. It also arises from the intermuscular septa of the arm, but more extensively from the medial than the lateral; it is separated from the lateral below by the brachioradialis and extensor carpi radialis longus muscles.
Its fibers converge to a thick tendon, which is inserted into the tuberosity of the ulna and the rough depression on the anterior surface of the coronoid process of the ulna.
[edit] Innervation
The brachialis muscle is innervated by the musculocutaneous nerve, which runs on its superficial surface, between it and the biceps brachii. Part of it is also innervated by the radial nerve (proprioceptive branch) which allows it to be split during certain approaches to the arm. The divide between the two innervations is at the insertion of the deltoid.
[edit] Actions
Unlike the biceps, the brachialis does not insert on the radius, and therefore cannot participate in pronation and supination of the forearm.
[edit] Variations
The muscle is occasionally doubled; additional slips to the supinator, pronator teres, biceps brachii, lacertus fibrosus, or radius are more rarely found.
[edit] Additional images
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Left humerus. Anterior view.
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Bones of left forearm. Anterior aspect.
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Nerves of the left upper extremity.
[edit] External links
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.
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