Brachialis muscle

The brachialis (brachialis anticus) is a muscle in the upper arm that flexes the elbow joint. It lies deeper than the biceps brachii, and makes up part of the floor of the region known as the cubital fossa. The brachialis is the prime mover of elbow flexion. While the biceps brachii appears as a large anterior bulge on the arm and commands considerable interest among body builders, the brachialis underlying it actually generates about 50% more power and is thus the prime mover of elbow flexion.[1]

Brachialis
Deep muscles of the chest and front of the arm, with the boundaries of the axilla. (Brachialis visible at bottom right.)
Position of brachialis (shown in red).
Details
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, brachial artery
Nerve	musculocutaneous nerve (C5-C7) and radial nerve (C5, C6)
Actions	flexion at elbow joint
Identifiers
Latin	musculus brachialis
TA	A04.6.02.018
FMA	37667
Anatomical terms of muscle

Structure

The brachialis originates from the anterior surface of the distal half of the humerus,[1] 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. Its fibers converge to a thick tendon, which is inserted into the tuberosity of the ulna[2] and the rough depression on the anterior surface of the coronoid process of the ulna.

Blood supply

The brachialis is supplied by the Muscular branches of brachial artery and the recurrent radial artery.[3]

Nerve supply

The brachialis muscle is innervated by the musculocutaneous nerve, which runs on its superficial surface, between it and the biceps brachii.[2] However, in 70-80% of people, the muscle has double innervation with the radial nerve (C5-T1). The divide between the two innervations is at the insertion of the deltoid.[4]

Variation

The muscle is occasionally doubled; additional slips to the supinator, pronator teres, biceps brachii, lacertus fibrosus, or radius are more rarely found. (A "slip" in this context refers to an accessory or variant part of a muscle that has an unusual trajectory in growth relative to the normal fibers' direction of growth.)

Function

The brachialis flexes the arm at the elbow joint.[2] Unlike the biceps, the brachialis does not insert on the radius, and does not participate in pronation and supination of the forearm.[2]

History

Etymology

The brachialis muscle[5] In classical Latin bracchialis means of or belonging to the arm,[6] and is derived from classical Latin bracchium,"arm".[6] The expression musculus brachialis is used in the current official anatomic nomenco[Terminologia Anatomica]].[7]

Additional images

• 
  Position of brachialis (shown in red). Animation.
• 
  Still image.
• 
  Horizontal section through the middle of upper arm. (Brachialis labeled at center left.)
• 
  Muscles of forearm, including insertion of brachialis tendon. Cross section. (Brachialis labeled at bottom left.)
• 
  Left humerus. Anterior view.
• 
  Bones of left forearm. Anterior aspect.
• 
  Nerves of the left upper extremity.
• 
  Brachialis muscle (labeled in green text)

See also

This article uses anatomical terminology.

References

This article incorporates text in the public domain from page 444 of the 20th edition of Gray's Anatomy (1918)

1. Saladin, Kenneth S, Stephen J. Sullivan, and Christina A. Gan. Anatomy & Physiology: The Unity of Form and Function. 2015. Print.
2. Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. p. 662,672. ISBN 978-0-8089-2306-0.
3. "Brachialis." UW Department of Radiology. University of Washington, Nov. 2005
4. "Brachialis Muscle." Kenhub. Kenhub, Aug. 2001
5. Di J.H. (Ed.) (1997).Stedman’s concise me10b">Triepel, H. (1910). Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit eitte Auflage). Wiesbaden: Verlag J.F. Bergmann.
6. Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.
7. Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme

External links

• Illustration: brachialis from The Department of Radiology at the University of Washington