Brachialis muscle

Template:Short description Template:Infobox muscle The brachialis (also brachialis anticus or Casserio muscle) is a muscle in the upper arm that flexes the elbow. It lies beneath the biceps brachii, and makes up part of the floor of the region known as the cubital fossa (elbow pit). It originates from the anterior aspect of the distal humerus;<ref name="Saladin, Kenneth S 2015" /> it inserts onto the tuberosity of the ulna. It is innervated by the musculocutaneous nerve,<ref name="GRAYS2005">Template:Cite book</ref> and commonly also receives additional innervation from the radial nerve.<ref name=":0">"Brachialis Muscle." Kenhub. Kenhub, Aug. 2001</ref> The brachialis is the prime mover of elbow flexion generating about 50% more power than the biceps.Template:Dubious<ref name="Saladin, Kenneth S 2015">Saladin, Kenneth S, Stephen J. Sullivan, and Christina A. Gan. Anatomy & Physiology: The Unity of Form and Function. 2015. Print.Template:Pn</ref>

Structure

Origin

The brachialis originates from the anterior surface of the distal half of the humerus,<ref name="Saladin, Kenneth S 2015" /> 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.<ref name="GRAYS2005" />

Insertion

Its fibers converge to a thick tendon which is inserted into the tuberosity of the ulna,<ref name="GRAYS2005" /> and the rough depression on the anterior surface of the coronoid process of the ulna.<ref>Template:Cite book Template:Pn</ref>

Innervation

The brachialis muscle is innervated by the musculocutaneous nerve (also Casserio nerve), which runs on its superficial surface, between it and the biceps brachii.<ref name="GRAYS2005" /> 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.<ref name=":0" />

Blood supply

The brachialis is supplied by muscular branches of the brachial artery and by the recurrent radial artery.<ref>"Brachialis." UW Department of Radiology. University of Washington, Nov. 2005</ref>

Variation

The muscle is occasionally doubled; additional muscle slips to the supinator, pronator teres, biceps brachii, lacertus fibrosus, or radius are more rarely found.Template:Citation needed

Function

The brachialis flexes the arm at the elbow joint.<ref name=GRAYS2005 /> Unlike the biceps, the brachialis does not insert on the radius, and does not participate in pronation and supination of the forearm.<ref name=GRAYS2005 />

History

Etymology

The brachialis muscle<ref name="Dirckx1997">Dirckx, J.H. (Ed.) (1997).Stedman’s concise medical dictionary for the health professions. (3rd edition). Baltimore: Williams & Wilkins.</ref> and brachial muscle<ref name="Dorland">Anderson, D.M. (2000). Dorland’s illustrated medical dictionary (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.Template:Pn</ref> can be considered as the anglicized variant of the Latin expression musculus bracchialis.<ref name="Triepel1910b">Triepel, H. (1910). Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit einem Anhang: Biographische Notizen.(Dritte Auflage). Wiesbaden: Verlag J.F. Bergmann.Template:Pn</ref> In classical Latin bracchialis means of or belonging to the arm,<ref name="Lewis & Short">Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.Template:Pn</ref> and is derived from classical Latin bracchium,"arm".<ref name="Lewis & Short"/> The expression musculus brachialis is used in the current official anatomic nomenclature Terminologia Anatomica.<ref name="FCAT">Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme.Template:Pn</ref>

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)