The parasympathetic nervous system (PNS) is the part of theautonomic nervous systemthat prepares the“relaxation response”in the body. It is mainly formed by cholinergic fibers and tends todecreasecontractility of cardiac muscle. But in smooth muscle, parasympathetic stimulation willincreasetone and contractility.

This“rest and digest”response has various possible effects on your body:

• 减少压力荷尔蒙勒vels
• The resting heart rate decreases, so less blood is being pumped into the muscles
• Respiration slows down due to low oxygen demand
• The digestive system is prioritized, so the blood flow to the gastrointestinal tract increases
• Pupils shrink
• Organs perform essential day-to-day functions

It consists of preganglionic and postganglionic fibers, both connected in the ganglia. The preganglionic fibers are long, while the latter is short (Figure 1).

Figure 1. Schematic representation of smooth or cardiac muscle parasympathetic control.There is only oneneurotransmitterpn的发布:acetylcholine(ACh)from both preganglionic and postganglionic fiber to the end organ. However, ACh binds to different receptors in this case: nicotinic receptors in the postganglionic fiber and muscarinic receptors in the end tissue.