The brain stem and spinal cord are recognized to be discrete parts of the body, but they are related both structurally and functionally. Located at the posterior end of the brain, the brain stem links the spinal cord to the rest of the brain. The spinal cord itself consists of 31 pairs of nerves as well as support cells in the spine. Both the brain stem and spinal cord have distinct roles as part of the central nervous system, but they depend on one another to accomplish their unique tasks.
Several different structures are contained within the brain stem, including some cranial nerve nuclei, the pons, the medulla, and the midbrain. The vasomotor and respiratory centers are located within the brain stem, which regulate breathing and blood pressure. Nerves travel through the brain stem to relay sensory information to the brain, and convey motor signals from the brain to the rest of the body.
The reticular activating system, which allows the body to be alert, is also found in the brain stem. Damage to this area can cause significant health issues, including a coma, or even death. The midbrain has several unique structures within its boundaries, some of which have important functions such as pain perception, some regulation of motor activity, and emotional regulation.
The spinal cord mostly lacks structures like those in the brain stem, but its nervous tissue allows information to be sent to and from the brain. One side of the spinal cord contains the dorsal root ganglia. These are responsible for sending sensory information, such as touch, to the brain.
Ventral roots deliver motor-related signals from the brain to mixed nerves, which then convey these signals to motor neurons. There is a small nerve coordinating center in the spinal cord. This allows for the execution of reflex actions, such as moving the body in response to pain.
The functions of the brain stem and spinal cord are linked in important ways. Signals to the central and peripheral nervous systems that arise in the brain stem often travel via the spinal cord to their destinations. These signals include such life-sustaining information as impulses that cause breathing. The spinal cord essentially allows the brain to communicate with the rest of the body. Even when signals to the body do not arise in the brain stem itself, it plays a necessary role by conveying information from the forebrain to the spinal cord.