Parasympathetic nerves are part of the autonomic nervous system, which controls involuntary bodily functions. They help the body relax and conserve energy by slowing the heart rate, increasing digestion, and promoting rest. This system is often referred to as the "rest and digest" system, counteracting the effects of the sympathetic nervous system, which prepares the body for stressful situations. These nerves originate in the brain and spinal cord, specifically from the brainstem and the sacral spinal cord. They release neurotransmitters like acetylcholine, which signal various organs to perform functions that support relaxation and recovery.