Coracobrachialis muscle

Structure

Origin

Coracobrachialis muscle arises from the (deep surface of the) apex of the coracoid process of the scapula (a common origin with the short head of the biceps brachii****). It additionally also arises from the proximal portion of tendon of origin of the biceps brachii muscle.

Insertion

It is inserted (by means of a flat tendon) into an impression at the middle of the medial border of the body of the humerus (shaft of the humerus) between the attachments of the medial head of the triceps brachii and the brachialis.

Innervation

Coracobrachialis muscle is perforated by and innervated by the musculocutaneous nerve, which arises from the anterior division of the upper trunk (C5, C6) and middle trunk (C7) of the brachial plexus.

Variation

The coracobrachialis muscle has been classified into distinct superficial and deep layers. In 16% of individuals the muscle is fully divided into these layers, in 8% of individuals there is incomplete separation, and in the 76% there is no discernible separation of the layers.

Function

The coracobrachialis is functionally insignificant. It is a weak**** flexor and adductor of the arm at the glenohumeral joint (shoulder joint).****

It additionally also resists deviation of the arm from the frontal plane during abduction.

Clinical significance

The overuse of the coracobrachialis can lead to stiffening of the muscle. Common causes of injury include chest workouts or activities that require one to press the arm very tight towards the body, e.g. work on the rings in gymnastics.

Symptoms of overuse or injury are pain in the arm and shoulder, radiating down to the back of the hand. In more severe cases, the musculocutaneous nerve can get trapped, causing disturbances in sensation to the skin on the radial part of the forearm and weakened flexion of the elbow, as the nerve also supplies the biceps brachii and brachialis muscles.

Rupture of the coracobrachialis muscle is extremely rare. Very few case reports exist in the literature, and it is reported to be caused by direct trauma to the contracted muscle. Avulsion of the muscle's origin from the coracoid as a result of indirect forces is even more unusual.

References

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Additional images

File:Coracobrachialis muscle - animation01.gif|Position of coracobrachialis muscle (shown in red). Animation. File:Coracobrachialis muscle - animation05.gif|Close up. Seen from below. Ribs are not shown. File:Coracobrachialis muscle07.png|Still image. Lateral view. File:Gray1231.png|Front of right upper extremity. (Coracobrachialis labeled at right, fourth from the bottom.) File:Slide7n.JPG|Coracobrachialis muscle (shown in green text) File:Slide5B.JPG|Coracobrachialis muscle (shown in green text). Horizontal section of arm. File:Slide1HHH.JPG|Coracobrachialis muscle (shown in green text) File:Slide1JJJ.JPG|Coracobrachialis muscle (shown in green text) File:Slide3OOO.JPG|Coracobrachialis muscle (shown in green text)

References

1. Sinnatamby, Chummy S.. (2011). "Last's Anatomy". Elsevier Australia.
2. Standring, Susan. (2020). "Gray's Anatomy: The Anatomical Basis of Clinical Practice".
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4. Spinner, Robert J.. (2018-01-01). "72 - Nerve Entrapment Syndromes". Elsevier.
5. (2016-07-05). "Bergman's Comprehensive Encyclopedia of Human Anatomic Variation". Wiley.
6. Mori, Masaru. (1964). "Statistics on the Musculature of the Japanese". Okajimas Folia Anatomica Japonica.
7. Saladin, Kenneth S. "The Muscular System." Anatomy & Physiology: The Unity of Form and Function. New York, NY: McGraw-Hill, 2012. 346. Print.
8. "Coracobrachialis Muscle And Pain" paintopia.com
9. "Coracobrachialis Muscle." Anatomy, Function and Pathology. KenHub.
10. Iannotti, Joseph P. and Gerald R. Williams. ''Disorders of the Shoulder: Diagnosis & Management, Volume 1'' Philadelphia: Lippincott Williams and Wilkins, 2007. 271–73. Print.