Which part of the autonomic nervous system is primarily responsible for stimulating involuntary functions?

The parasympathetic nervous system is primarily responsible for stimulating involuntary functions. Its main role is to promote a "rest and digest" response, which includes activities necessary for conserving energy, such as slowing the heart rate, increasing intestinal and gland activity, and relaxing sphincter muscles in the gastrointestinal tract. This system helps to maintain homeostasis by supporting functions that occur when the body is in a relaxed state.

This contrasts with the sympathetic nervous system, which prepares the body for "fight or flight" responses and activates functions that occur during stressful situations. The central nervous system is not specifically tied to involuntary function but is involved in processing information and responding to stimuli, while the peripheral nervous system encompasses nerves that extend beyond the central nervous system and includes both voluntary and involuntary nervous function. Therefore, the correct answer highlights the specific involuntary aspects managed by the parasympathetic division.