The brachial plexus is formed by the anterior rami of the spinal nerves C5 to T1. They are also known as the five roots of the brachial plexus. The roots merge to form three trunks of the brachial plexus:

• Superior trunk - formed by the anterior rami or roots of the C5 and C6 spinal nerves;
• Middle trunk - formed by the C7;
• Inferior trunk - formed by the C8 and T1.