The brachialis (also brachialis anticus or Casserio muscle) is a skeletal muscle in the upper arm that Elbow flexion. 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;["Brachialis Muscle." Kenhub. Kenhub, Aug. 2001] The brachialis is the agonist muscle of elbow flexion generating about 50% more power than the biceps.[Saladin, Kenneth S, Stephen J. Sullivan, and Christina A. Gan. Anatomy & Physiology: The Unity of Form and Function. 2015. Print.]
Structure
Origin
The brachialis originates from the anterior surface of the distal half 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.
Insertion
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.
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.
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.
Blood supply
The brachialis is supplied by muscular branches of the
brachial artery and by the recurrent
radial artery.
["Brachialis." UW Department of Radiology. University of Washington, Nov. 2005]
Variation
The muscle is occasionally doubled; additional
to the
supinator,
pronator teres,
biceps brachii, lacertus fibrosus, or radius are more rarely found.
Function
The brachialis flexes the arm at the elbow joint.
Unlike the biceps, the brachialis does not insert on the radius, and does not participate in
pronation and
supination of the forearm.
History
Etymology
The
brachialis muscle[Dirckx, J.H. (Ed.) (1997). Stedman’s concise medical dictionary for the health professions. (3rd edition). Baltimore: Williams & Wilkins.] and
brachial muscle[Anderson, D.M. (2000). Dorland’s illustrated medical dictionary (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.] can be considered as the anglicized variant of the
Latin expression
musculus bracchialis.
[Triepel, H. (1910). Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit einem Anhang: Biographische Notizen.(Dritte Auflage). Wiesbaden: Verlag J.F. Bergmann.] In
classical Latin bracchialis means
of or belonging to the arm,
[Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.] and is derived from classical Latin
bracchium,"arm".
The expression
musculus brachialis is used in the current official anatomic nomenclature
Terminologia Anatomica.
[Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme.]
Additional images
File:Brachialis muscle - animation03.gif|Position of brachialis (shown in red). Animation.
File:Brachialis muscle01.png|Still image.
File:Gray413 color.png|Horizontal section through the middle of upper arm. (Brachialis labeled at center left.)
File:Muscles of upper limb.(cross section - human cadaver).jpg|Muscles of forearm, including insertion of brachialis tendon. Cross section. (Brachialis labeled at bottom left.)
File:Gray207.png|Left humerus. Anterior view.
File:Gray213.png|Bones of left forearm. Anterior aspect.
File:Nerves_of_the_left_upper_extremity.gif|Nerves of the left upper extremity.
File:Slide10zzz.JPG|Brachialis muscle (labeled in green text)
See also
External links
