The main function of the coracobrachialis muscle is to produce flexion and adduction of the arm at the shoulder joint. Along with the other flexors of the arm (biceps brachii and brachialis muscles), coracobrachialis is innervated by the musculocutaneous nerve.
In this article, we will discuss the anatomy and function of the coracobrachialis muscle.
|Origin||Coracoid process of the scapula|
|Insertion||Anteromedial surface of the humerual shaft|
|Action||Adduction and flexion of the arm at the shoulder joint|
|Innervation||Musculocutaneous nerve (C5- C7)|
|Blood supply||Muscular branches of brachial artery|
Origin and insertion
The coracobrachialis is a slender muscle that originates from the deep surface of the coracoid process of scapula.
The muscle fibers run inferolaterally towards the humerus. They insert onto the anteromedial surface of the humeral shaft, between the brachialis muscle and the medial head of triceps.
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The coracobrachialis muscle lies posterior to the pectoralis major muscle and anterior to the tendons of subscapularis, latissimus dorsi, teres major and the medial head of triceps. The muscle is located medial to the biceps brachii and brachialis muscles. The humeral insertion of coracobrachialis is crossed anteriorly by the median nerve. Along with the humerus, coracobrachialis forms the lateral border of the axilla, where it is also the easiest to palpate the muscle.
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The coracobrachialis muscle is innervated by the musculocutaneous nerve (C5-C7) a branch of the lateral cord of the brachial plexus.
The main actions of the coracobrachialis muscle are bending the arm (flexion) and pulling the arm towards the trunk (adduction) at the shoulder joint. When the arm is abducted and extended, the coracobrachialis muscle acts as a strong antagonist to the deltoid muscle.
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The overuse of the coracobrachialis can lead to a hardening of the muscle. Common causes include, among others, bench pressing with extremely heavy weights and carrying heavy loads with hanging arms. A typical symptom is pain in the arm and shoulder, radiating down to the back of the hand.
In more severe cases the musculocutaneous nerve, which goes through the coracobrachialis, can become trapped (entrapment). Clinically, the affected patients show skin sensation disturbances on the radial part of the forearm and a weakened flexion in the elbow, as the nerve also supplies the biceps brachii and brachialis muscles. In contrast, an actual rupture of the coracobrachialis is extremely rare and almost only occurs in serious accidents.