Coracobrachialis is a muscle of the anterior compartment of the arm, found in the upper and medial part of the arm. It is also called Musculus Coracobrachialis; this muscle is a useful landmark in the arm for locating other structures in the arm such as identifying the musculocutaneous nerve which pierces this muscle in the axilla and this can be explained with knowledge of comparative anatomy whereby the muscle has three heads in some animals but in man, the two heads have fused thereby trapping the nerve between them while the third part has become suppressed. The occasional supratrochlear spur located on the anteromedial aspect of the lower humerus may be continuous with the ligament of Struthers which passes to the medial epicondyle and represents the remains of the third head. The median nerve or brachial artery or both may run beneath it and may become compressed.
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Coracobrachialis Origin and Insertion
Coracobrachialis muscle originates together with the short head of biceps brachii from the tip of the coracoid process of scapula and passes vertically downwards through the axilla to insert at the middle third of medial surface of humerus.
Coracobrachialis Function and Action
The Coracobrachialis muscle functions as a weak flexor and adductor of the arm (because the main adductors of the shoulder joint are the pectoralis major and latissimus dorsi) and also stabilizes the glenohumeral joint (shoulder joint). Another function is in its use a landmark structure for identifying other structures of the arm. As a useful landmark the distal part of attachment of Coracobrachialis muscle indicates the location of the nutrient foramen of the humerus, because the nutrient branch of the brachial artery runs along the lower border of me muscle. The musculocutaneous nerve pierces this muscle on its medial surface in the axilla.
Coracobrachialis Nerve Supply
Coracobrachialis muscle is innervated by the musculocutaneous nerve which pierces it (from C5, C6 and C7 cervical segments of the spinal cord; C6 being the main supply).
Coracobrachialis Blood Supply
The arterial blood supply of Coracobrachialis is from the brachial artery.
Clinical importance of Coracobrachialis
Coracobrachialis can become hardened by too much use of the muscle during activities such as carrying heavy loads with hanging arms leading to signs and symptoms such as pain in the arm and shoulder that radiates to the back of the hand this is typical of Coracobrachialis. When this muscle becomes severely overused, it could cause nerve entrapment of musculocutaneous nerve and since this nerve also supplies biceps brachii and brachialis muscles, its entrapment could lead to weak flexion of the elbow. The clinical signs and symptoms of entrapment are altered skin sensation on the radial part of the forearm as well as the weakened flexion of the elbow.