Musculocutaneous nerve

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Nerve: Musculocutaneous nerve
Nerves of the left upper extremity.
Cutaneous nerves of right upper extremity. Anterior view.
Latin nervus musculocutaneus
Gray's subject #210 935
Innervates Biceps brachii
Brachioradialis
Coracobrachialis
From lateral cord

The musculocutaneous nerve arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis minor, its fibers being derived from the fifth, sixth, and seventh cervical nerves.

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[edit] Path

It pierces the Coracobrachialis muscle and passes obliquely between the Biceps brachii and the Brachialis, to the lateral side of the arm; a little above the elbow it pierces the deep fascia lateral to the tendon of the Biceps brachii and is continued into the forearm as the lateral antibrachial cutaneous nerve.

In its course through the arm it innervates the Coracobrachialis, Biceps brachii, and the greater part of the Brachialis.

The branch to the Coracobrachialis is given off from the nerve close to its origin, and in some instances as a separate filament from the lateral cord of the plexus; it is derived from the seventh, cervical nerve.

The branches to the Biceps brachii and Brachialis are given off after the musculocutaneous has pierced the Coracobrachialis; that supplying the Brachialis gives a filament to the elbow-joint.

The nerve also sends a small branch to the bone, which enters the nutrient foramen with the accompanying artery.

[edit] Irregularities

The musculocutaneous nerve presents frequent irregularities.

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.

[edit] Damage

Although rare, the musculocutaneous n. can be affected through compression due to hypertrophy or entrapment between the biceps aponeurosis & brachialis fascia or it may be injured through stretch as occurs in dislocations & sometimes in surgery

Isolated injury, causes weakness of elbow flexion & supination of the forearm

A discrete sensory disturbance is present on the radial side of the forearm

The nerve is usually involved in an upper brachial plexus palsy

Injury can occur before entering the coracobrachialis due to dislocation or apparently due to stretch due to throwing injury

Heavy backpacks can cause damage to the upper trunk of the brachial plexus – dysfunction can be severe & prolonged with similar injury as occurs with Erb’s palsy from breech deliveries. Early detection is important – the combination of time, avoidance of wearing a backpack, & strengthening of the shoulder muscles will probably be effective.

Distal to the coracobrachialis, the MC cause appears to be weight lifting – either through compression due to hypertrophy or entrapment between the biceps & brahcialis, the nerve may lead to a painless loss of muscle strength in flexion & supination of the forearm. ® Initial treatment should include avoidance of biceps curls or other biceps exercises.

Initial treatment should include avoidance of biceps curls or other biceps exercises.

[edit] Additional images

[edit] External links

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.

Brachial plexus

supraclavicular: dorsal scapular - suprascapular - to the subclavius - long thoracic

infraclavicular: lateral cord: musculocutaneous (lateral cutaneous of forearm) - lateral pectoral - lateral head of median

medial cord: medial pectoral - medial cutaneous of forearm - medial cutaneous cutaneous of arm - ulnar (palmar branch - dorsal branch) - medial head of median

posterior cord: upper subscapular - lower subscapular - thoracodorsal - axillary (superior lateral cutaneous of arm) - radial (muscular - posterior cutaneous of arm - posterior cutaneous of forearm - superficial branch - deep branch)

median: anterior interosseous - palmar - proper palmar digital - common palmar digital

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