Final answer:
The brachial plexus innervates the regions of the shoulder, arm, forearm, and hand, and is formed by nerve fibers from spinal segments C4 through T1.
Step-by-step explanation:
The brachial plexus innervates the arm and is associated with the lower cervical spinal nerves and the first thoracic spinal nerve. The nerves generated from this plexus specifically innervate regions including the shoulder, arm, forearm, and the hand.
It is comprised of spinal nerves C4 through T1 which reorganize to give rise to several major nerves, such as the radial nerve, the axillary nerve, the ulnar nerve, and the median nerve. The radial nerve, for example, continues through the arm and is paralleled by the ulnar and the median nerves, which also extend and supply various regions within the arm and hand.