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Posterior Division of Middle Trunk of Brachial Plexus
Nervous System

Posterior Division of Middle Trunk of Brachial Plexus

Divisio posterior trunci medii plexus brachialis

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Quick Facts

Origin: Middle trunk of the brachial plexus.

Course: From posterior to the mid-clavicle inferolaterally to a position posterior to the first segment of the axillary artery.

Branches: No branches. Contributes to two of the nerves derived from the posterior cord.

Supply: Sensory and motor innervation. Supplies sensory innervation for the skin of the posterolateral surface of the hand, and the posterior and lateral skin of the arm and forearm. Motor innervation is to the posterior compartment muscles of the arm and forearm, and the latissimus dorsi.

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Origin

The origin of the posterior 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 posterior division of the middle trunk forms on the border of the posterior triangle and the axilla, roughly posterior to the mid-clavicle. It runs inferolaterally, assuming a position posterior to the first segment of the axillary artery.

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

Branches

The posterior division of the middle trunk itself has no branches as it generally does not give rise to any nerves. However, it merges with the posterior divisions of the superior and inferior trunks to form the posterior cord. The contribution of the posterior division of the middle trunk to this cord gives rise to the following nerves:

—thoracodorsal nerve;

—radial nerve.

The posterior division of the middle trunk merges to form the posterior cord, it gives either little or no contribution to the upper and lower subscapular nerves, and no contribution to the axillary nerve.

Supplied Structures

The posterior division of the middle trunk supplies some of the structures innervated by the posterior cord. This includes posterior and lateral surfaces of the arm forearm, and hand (sensory) and the muscles of the posterior compartment of the arm and forearm (motor). Broken down by nerve, the structures supplied by the posterior division of the middle trunk are:

—thoracodorsal nerve supplies motor innervation of the latissimus dorsi muscle;

—radial nerve supplies sensory to skin of the posterolateral arm, posterior forearm, and posterolateral hand and motor innervation to the muscles of the posterior compartment of the arm and forearm.

Minor contributions to the following structures can occur:

—upper subscapular nerve supplies motor innervation of the subscapularis muscle;

—lower subscapular nerve supplies motor innervation of the subscapularis muscle.

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