Which nervous system division is involved in involuntary actions, such as heart rate and digestion?

The autonomic nervous system is the correct answer because it is responsible for regulating involuntary physiological processes, including heart rate, blood pressure, respiration, digestion, and sexual arousal. This system operates largely below the level of consciousness and allows the body to maintain homeostasis without the need for conscious effort.

The autonomic nervous system is further divided into two main branches: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system prepares the body for "fight or flight" responses during stressful situations, while the parasympathetic nervous system is involved in "rest and digest" functions that promote relaxation and conservation of energy.

In contrast, the central nervous system comprises the brain and spinal cord and is primarily involved in processing sensory information and coordinating responses. The somatic nervous system, on the other hand, controls voluntary movements by innervating skeletal muscles. Thus, the autonomic nervous system specifically addresses involuntary actions, making it the best fit for the question regarding heart rate and digestion.