Posterior division of superior trunk of brachial plexus

At a glance

English

Posterior division of superior trunk of brachial plexus

Latin (TA2)

Divisio posterior trunci superioris plexus brachialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the posterior division of superior trunk of brachial plexus

The superior trunk of the brachial plexus is formed by the ventral rami of the fifth and sixth cervical nerves at the lateral edge of scalenus medius. After giving the suprascapular nerve and the nerve to subclavius, it splits behind the middle of the clavicle into two divisions. The posterior division carries fibres destined for the muscles on the back, or extensor, side of the limb.

It passes behind the axillary artery and unites with the posterior divisions of the middle and inferior trunks to form the posterior cord. Through that cord its C5 and C6 fibres reach the upper and lower subscapular nerves, the axillary nerve and the radial nerve. In this way it contributes to subscapularis, teres major, the deltoid and teres minor, and through the radial nerve to brachioradialis, supinator and the upper extensors of the wrist. Its sensory fibres pass to the skin over the deltoid and the back of the arm and forearm through the cutaneous branches of the same nerves.

When the upper trunk is stretched, for example by a fall that drives the head away from the shoulder, loss of this division adds to that of the anterior division. The deltoid and teres minor no longer abduct and laterally rotate the arm, and brachioradialis and supinator no longer help bend the elbow and turn the palm up. Together with the loss of the elbow flexors from the anterior division, this gives the arm hanging at the side and turned inwards, typical of an upper plexus palsy.

Course and supply

Arises from

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

Ends in

Joins the posterior divisions of the middle and inferior trunks to form the posterior cord, whose branches are the subscapular, thoracodorsal, axillary and radial nerves.

Supplies

Carries motor fibres to subscapularis, teres major, the deltoid, teres minor, brachioradialis, supinator and the upper wrist extensors, and sensory fibres from the shoulder and back of the limb.