The parasympathetic nervous system (PNS) is a crucial part of the body's autonomic nervous system, which controls involuntary functions. It helps the body relax and recover after stress. The PNS regulates heart rate, digestion, breathing, and other bodily functions. It uses a neurotransmitter called acetylcholine to send signals. For example, it slows down the heart rate, helps with digestion by contracting bowel muscles, and regulates breathing after stress. The PNS also manages mucus production in the lungs and constricts pupils to help us see close objects. Four cranial nerves in the PNS help with senses like smell and taste, and the vagus nerve, which makes up about 75% of the PNS, connects to many organs, including the heart and digestive tract. Keeping the PNS healthy involves reducing stress and maintaining a healthy lifestyle. If you notice issues with heart rate, digestion, or other functions, it's important to see a doctor.