Final answer:
The brachial plexus is a nerve plexus formed by the lower cervical and upper thoracic spinal nerves, which branches out to form the radial, ulnar, and median nerves, providing motor and sensory functions to the arms.
Step-by-step explanation:
The brachial plexus is a network of nerves that originates from the lower cervical and upper thoracic spinal nerves (C4 through T1). It reorganizes these nerves to give rise to the nerves that supply the arms. The radial nerve is a significant nerve from this plexus, which then gives off the axillary nerve heading to the armpit area. The radial nerve also runs through the arm alongside other major nerves such as the ulnar nerve and the median nerve. Each of these nerves, derived from the brachial plexus, provides motor and sensory functions to different parts of the arm, enabling movements and sensations.