Final answer:
The autonomic nervous system is responsible for regulating involuntary functions like heart rate and breathing, allowing them to occur without conscious effort.
Step-by-step explanation:
The autonomic nervous system (ANS) is responsible for involuntary control of the body, usually for the sake of homeostasis (regulation of the internal environment). It controls activities such as heart rate, blood flow, and digestion without conscious awareness or voluntary participation. For example, when Stephanie walks to class, her heart pumps on its own and she does not have to think about breathing because these functions are regulated by the autonomic nervous system.