Anterior division of inferior trunk of brachial plexus

At a glance

English

Anterior division of inferior trunk of brachial plexus

Latin (TA2)

Divisio anterior trunci inferioris plexus brachialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the anterior division of inferior trunk of brachial plexus

The brachial plexus is built in stages: roots, trunks, divisions, cords and branches. The inferior trunk forms from the ventral rami of the eighth cervical and first thoracic nerves, which unite behind the subclavian artery as they arch over the first rib. Near the lateral border of the rib, behind the clavicle, the trunk splits into an anterior and a posterior division. The anterior division carries fibres for the front (flexor) compartments of the limb, the posterior division fibres for the back.

Unlike the anterior divisions of the upper two trunks, which merge, this division does not join any other. It runs on alone, lying behind and then medial to the axillary artery, and becomes the medial cord as it enters the axilla. Its fibres therefore end in the branches of that cord: the medial pectoral nerve, the medial cutaneous nerves of the arm and forearm, the ulnar nerve and the medial root of the median nerve.

Through these branches the division supplies most of the small muscles of the hand, the flexors on the ulnar side of the forearm, the long finger flexors in part and pectoralis minor and part of pectoralis major. Its sensory territory includes the medial side of the arm, forearm and hand. Sympathetic fibres reaching the limb also travel through the lower roots.

Because the inferior trunk lies low over the first rib, it is most often involved in compression and traction injuries. A cervical rib or fibrous band can press on it in thoracic outlet syndrome, causing pain and wasting of the hand. Forceful upward pulling of the arm injures the lower roots and trunk, producing Klumpke palsy with a clawed hand. A tumour at the lung apex can invade the lower plexus from below.

Course and supply

Arises from

Inferior trunk of the brachial plexus (C8 and T1), dividing behind the clavicle near the lateral border of the first rib.

Ends in

Continues as the medial cord, giving the medial pectoral, medial cutaneous, ulnar and part of the median nerve.

Supplies

Carries motor fibres to the anterior forearm flexors on the ulnar side, most of the intrinsic hand muscles and the pectorals, and sensory fibres from the medial arm, forearm and hand.