Anterior division of superior trunk of brachial plexus

At a glance

English

Anterior division of superior trunk of brachial plexus

Latin (TA2)

Divisio anterior trunci superioris plexus brachialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the anterior division of superior trunk of brachial plexus

The superior trunk of the brachial plexus forms when the ventral rami of the fifth and sixth cervical nerves unite near the lateral edge of scalenus medius, at a spot on the side of the neck known as Erb's point. Before it divides, the trunk gives the suprascapular nerve and the small nerve to subclavius. Behind the clavicle it then splits into anterior and posterior divisions, the anterior one carrying fibres for the flexor compartments of the limb.

This anterior division joins the anterior division of the middle trunk to form the lateral cord, which lies lateral to the axillary artery behind pectoralis minor. Its fibres reach their targets through the branches of that cord: the lateral pectoral nerve, the musculocutaneous nerve and the lateral root of the median nerve.

Its fifth and sixth cervical fibres are the main supply of the elbow flexors, biceps and brachialis, through the musculocutaneous nerve, and of coracobrachialis. They also give pectoralis major its clavicular fibres and add to the median nerve, mainly for pronator teres and flexor carpi radialis. The sensory fibres carried end in the skin of the lateral forearm and the thumb side of the hand.

Injury to the upper trunk is the commonest pattern of brachial plexus damage. A fall onto the shoulder or a motorcycle crash can force the head and shoulder apart and stretch the C5 and C6 roots, producing Erb palsy. Loss of the anterior division's targets explains why the elbow cannot bend and the forearm stays pronated, while loss of the posterior division and suprascapular nerve leaves the arm hanging in medial rotation, the waiter's tip posture. Nerve transfers to the musculocutaneous nerve are a common repair.

Course and supply

Arises from

Superior trunk of the brachial plexus (C5 and C6), dividing behind the clavicle.

Ends in

Joins the anterior division of the middle trunk to form the lateral cord, which gives the lateral pectoral, musculocutaneous and lateral root of the median nerve.

Supplies

Carries motor fibres to biceps, brachialis, coracobrachialis, pectoralis major and some forearm flexors, and sensory fibres from the lateral forearm and thumb side of the hand.