The autonomic system, a complex subset of the peripheral nervous system, controls involuntary activities, such as heart rate, temperature, and the smooth muscle activity of the vascular and digestive systems.
The brain stem is an automatic control center for many such important involuntary actions of the body. ... The brain stem helps serve this purpose. It regulates heartbeat and respiration. It helps to wake up the rest of the brain from sleep by activating the other areas.
