What part of the peripheral nervous system controls involuntary actions like heartbeat?

The autonomic nervous system is the correct answer because it is specifically responsible for regulating involuntary bodily functions, such as heartbeat, digestion, and respiratory rate. It operates automatically, without conscious effort, and regulates the activity of internal organs, making it essential for maintaining homeostasis.

The autonomic nervous system is further divided into two main branches: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system generally prepares the body for "fight or flight" responses, which can increase heart rate and blood pressure during stressful situations. In contrast, the parasympathetic nervous system promotes "rest and digest" functions, slowing down the heart rate and allowing for energy conservation and recovery.

The somatic nervous system, on the other hand, is responsible for voluntary movements and controlling skeletal muscles, which is separate from the involuntary actions governed by the autonomic system. Therefore, the autonomic nervous system is the primary controller of involuntary actions like heartbeat.