Anatomy of the brachial plexus

Have you ever fallen asleep with your shoulder in a weird position only to wake up to your arm completely asleep? Or hit the inside of your elbow, or the famous ‘funny bone’, and cause part of your hand to go numb?

This happens when we compress or bang the nerves found in our arms, all of which originate in the brachial plexus. The brachial plexus is a vast network of nerves originating from the anterior rami of C5 to T1, which extends through the axilla into the shoulder, arm, and hand, providing afferent, or sensory, nerve fibers from the skin, as well as efferent, or motor, nerve fibers to the muscles.

Alright, so, the brachial plexus is divided into five roots, three trunks, six divisions, three cords, and five terminal branches. The order can be remembered using the mnemonic. “Remember To Drink Cold Beer.”

Additionally, there are branches that leave the brachial plexus at various points along its length. Since the branches that come off of the roots and trunks are located above the clavicle, they are sometimes called the supraclavicular branches of the brachial plexus.

And since the branches that come off of the cords as well as the terminal branches are located below the clavicle, they are sometimes called the infraclavicular branches of the brachial plexus.

Okay, so starting with the roots, the five roots come from the anterior rami of the last four cervical nerves, C5-C8, as well as the anterior ramus of the first thoracic nerve or T1. These roots usually travel between the anterior and middle scalene muscles along with the subclavian artery.

These five roots give off some branches: the long thoracic nerve, which arises from C5-C7, and gives motor innervation to the serratus anterior muscle, the dorsal scapular nerve from C5, which gives motor innervation to the rhomboid and levator scapulae muscles, and a contribution to the phrenic nerve from C5, which gives motor and sensory innervation to the diaphragm.

At the inferior part of the neck, the five roots combine to form three trunks: C5 and C6 merge to form the superior or upper trunk, C7 remains as the middle trunk, and C8 and T1 merge to form the inferior or lower trunk.