Anterior division of middle trunk of brachial plexus

At a glance

English

Anterior division of middle trunk of brachial plexus

Latin (TA2)

Divisio anterior trunci medii plexus brachialis

System

Nerve

Region

Upper limb

Side

Paired, left and right

About the anterior division of middle trunk of brachial plexus

The middle trunk of the brachial plexus is formed by the ventral ramus of the seventh cervical nerve alone. It runs laterally between the scalene muscles and across the posterior triangle of the neck, and behind the clavicle it splits into an anterior and a posterior division. As in the other trunks, the anterior division takes fibres destined for the flexor compartments of the limb, and the posterior division those for the extensors.

The anterior division of the middle trunk joins the anterior division of the superior trunk, usually just below or behind the clavicle, to form the lateral cord. This cord lies lateral to the second part of the axillary artery, behind pectoralis minor. Its fibres reach the arm through the lateral cord's branches: the lateral pectoral nerve, the musculocutaneous nerve and the lateral root of the median nerve. Some seventh cervical fibres also cross from the lateral cord to the ulnar nerve.

By these routes the division contributes motor supply to pectoralis major, to the flexor muscles of the forearm through the median nerve, and to coracobrachialis and the elbow flexors through the musculocutaneous nerve, together with sensory fibres to the lateral forearm and the radial side of the hand. The seventh cervical root is a major source of fibres for the median nerve.

Isolated injury to the middle trunk is uncommon; it is usually involved with the upper trunk in severe traction injuries, adding weakness of the forearm flexors to the classic upper-plexus pattern. In some operations to restore function after plexus injury, the healthy seventh cervical root from the opposite side is transferred as a donor nerve. The divisions are a target for local anaesthetic in supraclavicular and infraclavicular blocks.

Course and supply

Arises from

Middle trunk of the brachial plexus (C7), dividing behind the clavicle.

Ends in

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

Supplies

Carries motor fibres to pectoralis major and the anterior arm and forearm muscles, and sensory fibres from the lateral forearm and radial side of the hand.