Final answer:
The brachial plexus is a nerve network responsible for the arm's motor and sensory functions, with its trunks formed by the lower cervical and first thoracic spinal nerves. These trunks lead to the division of nerves that provide the necessary control over the arm's movements and sensations.
Step-by-step explanation:
The brachial plexus is a nerve plexus associated with the lower cervical spinal nerves (C4 through C8) and the first thoracic spinal nerve (T1). It reorganizes these spinal nerves to give rise to the nerves that control the muscles and provide sensation to the arms. Specifically, the brachial plexus has trunks that are formed by the union of the anterior rami of these spinal nerves. These trunks then divide into divisions and further form cords that give rise to various important nerves such as the radial nerve, the axillary nerve, the ulnar nerve, and the median nerve. The radial nerve and its branches, such as the axillary nerve, are responsible for motor and sensory functions in the arm, with the radial nerve being important for cutaneous sensation and motor control.
The trunks of the brachial plexus play a crucial role as they form the basis for the organization and branching of nerves that control arm functions. This plexus contains fibers serving both sensory and motor functions, highlighting the complexity and significance of this network in the human body's nervous system.