The musculocutaneous nerve arises from the

lateral cord The lateral cord is the part of the brachial plexus formed by the anterior divisions of the upper (C5-C6) and middle trunks (C7). Its name comes from it being lateral to the axillary artery as it passes through the axilla. The other cords of the br ...

of the

brachial plexus The brachial plexus is a network () of nerves formed by the anterior rami of the lower four cervical nerves and first thoracic nerve ( C5, C6, C7, C8, and T1). This plexus extends from the spinal cord, through the cervicoaxillary canal in th ...

, opposite the lower border of the

pectoralis major The pectoralis major () is a thick, fan-shaped or triangular convergent muscle, situated at the chest of the human body. It makes up the bulk of the chest muscles and lies under the breast. Beneath the pectoralis major is the pectoralis minor, a ...

, its fibers being derived from C5, C6 and C7.

Structure

The musculocutaneous nerve arises from the lateral cord of the brachial plexus, courses through the anterior part of the arm, and terminates at 2 cm above elbow as the

lateral cutaneous nerve of the forearm The lateral antebrachial cutaneous nerve (or lateral cutaneous nerve of forearm) (branch of musculocutaneous nerve, also sometimes spelled "antebrachial") passes behind the cephalic vein, and divides, opposite the elbow-joint, into a volar and a ...

. Musculocutaneous nerve arises from the lateral cord of the brachial

plexus In neuroanatomy, a plexus (from the Latin term for "braid") is a branching network of vessels or nerves. The vessels may be blood vessels (veins, capillaries) or lymphatic vessels. The nerves are typically axons outside the central nervous syste ...

with root value of C5 to C7 of the spinal cord. It follows the course of the third part of the

axillary artery In human anatomy, the axillary artery is a large blood vessel that conveys oxygenated blood to the lateral aspect of the thorax, the axilla (armpit) and the upper limb. Its origin is at the lateral margin of the first rib, before which it is c ...

(part of the axillary artery distal to the

pectoralis minor Pectoralis minor muscle () is a thin, triangular muscle, situated at the upper part of the chest, beneath the pectoralis major in the human body. Structure Attachments Pectoralis minor muscle arises from the upper margins and outer surfaces ...

) laterally and enters the frontal aspect of the arm where it penetrates the

coracobrachialis The coracobrachialis muscle is the smallest of the three muscles that attach to the coracoid process of the scapula. (The other two muscles are pectoralis minor and the short head of the biceps brachii.) It is situated at the upper and medial part ...

muscle. It then passes downwards and laterally between the biceps brachii (above) and the brachialis muscles (below), to the lateral side of the arm; at 2 cm above the elbow it pierces the

deep fascia Deep fascia (or investing fascia) is a fascia, a layer of dense connective tissue that can surround individual muscles and groups of muscles to separate into fascial compartments. This fibrous connective tissue interpenetrates and surrounds the m ...

lateral to the tendon of the biceps brachii and is continued into the forearm as the

. In its course through the arm it innervates the coracobrachialis, biceps brachii, and the greater part of the brachialis. Its terminal branch, the lateral cutaneous nerve of the forearm, supplies the sensation of the lateral side of the forearm from the elbow to the wrist. Besides, the musculocutaneous nerve also gives articular branches to the elbow joint and to the humerus.

Variations

The musculocutaneous nerve presents frequent variations and communications with the median nerve. #It may adhere for some distance to the median and then pass outward, beneath the biceps brachii, instead of through the coracobrachialis. #Some of the fibers of the median may run for some distance in the musculocutaneous and then leave it to join their proper trunk; less frequently the reverse is the case, and the median sends a branch to join the musculocutaneous. #The nerve may pass under the coracobrachialis or through the biceps brachii. #Occasionally it gives a filament to the pronator teres, and it supplies the dorsal surface of the thumb when the superficial branch of the radial nerve is absent.

Nerve injuries

Injury to the musculocutaneous nerve can be caused by three mechanisms: repeated microtrauma, indirect trauma or direct trauma on the nerve. Overuse of coracobrachialis, biceps, and brachialis muscles can cause the stretching or compression of musculocutaneous nerve. Those who have it can complain of pain, tingling or reduced sensation over the lateral side of the forearm. This symptom can be reproduced by pressing over the region below the

coracoid process The coracoid process (from Greek κόραξ, raven) is a small hook-like structure on the lateral edge of the superior anterior portion of the scapula (hence: coracoid, or "like a raven's beak"). Pointing laterally forward, it, together with the ...

(positive

Tinel's sign Tinel's sign (also Hoffmann-Tinel sign) is a way to detect irritated nerves. It is performed by lightly tapping ( percussing) over the nerve to elicit a sensation of tingling or " pins and needles" in the distribution of the nerve. Percussion is u ...

). Pain can also be reproduced by flexing the arm against resistance. Other differential diagnoses that can mimick the symptoms of musculocutaneous palsy are: C6 radiculopathy (pain can be produced by movement of the neck), long head of biceps tendinopathy (no motor or sensory deficits), pain of the

bicipital groove The bicipital groove (intertubercular groove, sulcus intertubercularis) is a deep groove on the humerus that separates the greater tubercle from the lesser tubercle. It allows for the long tendon of the biceps brachii muscle to pass. Structure ...

(relieved by shoulder joint injection). Electromyography test shows slight neural damage at the biceps and the brachialis muscles with slower motor and sensory conduction over the Erb's point. In indirect trauma, violent abduction and retroposition of the shoulder can stretch the nerve and result tension of the

with musculocutaneous nerve lesion. Those with this type of lesion is presented with pain, reduced sensation, and tingling of the lateral part of forearm (lateral antebrachial cutaneous nerve - terminal sensory only branch of Musculocutaneous nerve) with reduced strength of elbow flexion. Tinel's sign can be positive. Differential diagnosis includes C5 and C6 nerve root lesions of the brachial plexus where the abduction, external rotation, and elbow flexion is lost. On the other hand, rupture of the biceps can cause the loss of flexion of the elbow without sensory deficits. Rupture of the SHORT HEAD of the biceps can decrease elbow flexion strength, where the brachialis muscle is intact. Rupture of the LONG HEAD of the biceps results in mild weakening of forearm supination as long as the supinator muscle is intact.

Electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyog ...

test is negative. In direct trauma, fracture of the humerus, gun shot, glass pieces injuries and more, can cause the musculocutaneous nerve lesion. Iatrogenic nerve injuries (for example during orthopedic surgery involving an internal fixation of the humerus) are relatively common and in a certain percentage of cases probably inevitable, though an adequate knowledge of the surgical anatomy can help to reduce its frequency.

Neurolysis Neurolysis is the application of physical or chemical agents to a nerve in order to cause a temporary degeneration of targeted nerve fibers. When the nerve fibers degenerate, it causes an interruption in the transmission of nerve signals. In the med ...

and nerve grafting are the treatment options for the above lesions.

References

External links

* * {{DEFAULTSORT:Musculocutaneous Nerve Nerves of the upper limb