Brachial plexus: the upper limb’s nerve network

Focused anatomy lesson

One network, many routes

A plexus is a joined network of nerves. The brachial plexus is part of the peripheral nervous system and links spinal nerve roots with the nerves serving much of the upper limb.

Location

The brachial plexus begins in the lower part of the neck and continues towards the axilla, the space beneath the shoulder. Its roots pass between the scalene muscles alongside the subclavian artery before joining into larger pathways.

From the axilla, the network gives rise to nerves that travel into the shoulder, arm, forearm, and hand. Other branches reach nearby muscles in the neck and thorax.

Formation

The arrangement is often remembered as roots, trunks, divisions, cords, and branches. Each stage combines or separates nerve fibres into routes that can reach different parts of the upper limb.

Roots

The roots are the anterior rami of spinal nerves C5, C6, C7, C8, and T1. These five roots form the starting point of the plexus.

Trunks and divisions

Three trunks are formed from the roots:

• Superior trunk: C5 and C6.
• Middle trunk: C7.
• Inferior trunk: C8 and T1.

Each trunk separates into an anterior and a posterior division. This creates routes that will later join to form the cords.

Cords and branches

The divisions form three cords named in relation to the axillary artery:

• Lateral cord: formed by the anterior divisions of the superior and middle trunks.
• Posterior cord: formed by the posterior divisions of all three trunks.
• Medial cord: formed by the anterior division of the inferior trunk.

Important terminal branches include the musculocutaneous, axillary, radial, median, and ulnar nerves. Additional branches include the long thoracic, dorsal scapular, suprascapular, and subclavian nerves.

Distribution

The branches of the brachial plexus carry motor instructions to muscles and sensory information back from skin and deeper tissues. Together, they support movement and sensation across most of the upper limb.

• The musculocutaneous nerve serves major muscles that bend the elbow and carries sensation from part of the lateral forearm.
• The axillary nerve serves the deltoid region and nearby skin.
• The radial nerve serves many extensor muscles and areas of skin on the posterior arm and forearm.
• The median and ulnar nerves serve different muscle and skin territories in the forearm and hand.
• The long thoracic, dorsal scapular, suprascapular, and subclavian nerves serve muscles around the shoulder and chest.

Clinical importance

Because the brachial plexus contains pathways for both movement and sensation, an injury can affect several functions at once. Stretching, compression, or direct injury near the neck, shoulder, or axilla may cause pain, altered sensation, weakness, or reduced movement.

The pattern depends on which roots, trunks, cords, or branches are affected. A problem involving the upper roots can affect shoulder and elbow movement, while pressure on lower pathways may alter function farther down the arm and hand.

Summary

The brachial plexus is a network formed by spinal nerves C5–T1. Its roots join into three trunks, divide into anterior and posterior pathways, and then form lateral, posterior, and medial cords. These cords and related branches supply much of the shoulder and upper limb.

Learning the sequence from roots to branches makes this complex network easier to map and helps explain why the location of an injury influences the symptoms that follow.