Anterior Division of Middle Trunk of Brachial Plexus

Origin

The origin of the anterior division of the middle trunk is from the middle trunk itself. This occurs when the trunk bifurcates into anterior and posterior divisions. It carries fibers from the C7 spinal segment.

Course

The anterior division forms roughly posterior to the mid-clavicle. It runs inferolaterally, posterior to the first segment of the axillary artery. Here, the anterior division of the middle trunk merges with the anterior division of the superior trunk to become the lateral cord.

The divisions of the brachial plexus run within the prevertebral fascia or its inferior extension, the axillary sheath.

Branches

The anterior division of the middle trunk itself has no branches as it generally does not give rise to any nerves. However, it merges with the anterior division of the superior trunk to form the lateral cord, and this cord gives rise or contributes to the following nerves:

—lateral pectoral nerve;

—musculocutaneous nerve;

—median nerve.

Supplied Structures

The anterior division of the middle trunk supplies the structures innervated by the lateral cord. In general, this represents anterior and lateral surfaces of the forearm, hand, and fingers (sensory) and the muscles of the hand and anterior compartments of the arm and forearm (motor). Broken down by nerve, the structures supplied by the anterior division of the middle trunk are:

—lateral pectoral nerve supplies motor innervation to the pectoralis major muscles and, through the ansa pectoralis, a minor contribution to the pectoralis minor muscle;

—musculocutaneous nerve supplies sensory innervation to the skin of the lateral forearm. Motor innervation of the muscles of the anterior compartment of the arm;

—median nerve innervates skin of the lateral palmar surface of the hand and finger tips and all intrinsic muscles of the hand and forearm flexors not innervated by the ulnar nerve.