Which nerve roots make up the brachial plexus?

The brachial plexus is a complex network of nerves that innervates the upper limb and is formed by the ventral rami of specific cervical and thoracic nerve roots. In particular, the brachial plexus is comprised of nerve roots from C5 to T1.

These specific nerve roots combine to form trunks, divisions, cords, and ultimately the peripheral nerves that supply motor and sensory functions to the arm. C5 and C6 typically contribute to innervating muscles around the shoulder and upper arm, while C7 plays a crucial role in extending the arm, and C8 and T1 are essential for the muscles of the forearm and hand.

The other options incorrect because they either include nerve roots that are not part of the brachial plexus—such as C3 and C4, which are involved in the cervical plexus—or they exclude essential roots like T1.