Which part of the nervous system includes the brain stem?

The brain stem is an essential component of the central nervous system (CNS), which consists of the brain and spinal cord. The brain stem itself is located at the base of the brain and connects the brain to the spinal cord, playing a crucial role in regulating vital functions such as heartbeat, breathing, and blood pressure. Additionally, it serves as a pathway for signals traveling between different parts of the nervous system.

In contrast, the other options represent different aspects of the nervous system that do not include the brain stem. The peripheral nervous system refers to the network of nerves outside the brain and spinal cord, which connects the CNS to limbs and organs. The somatic nervous system controls voluntary movements of skeletal muscles, while the autonomic nervous system regulates involuntary functions such as heart rate and digestion. Neither of these systems encompasses the brain stem, which is strictly part of the CNS.