The parasympathetic nervous system, PNS, is the branch of the autonomic nervous system that supports relaxation and recovery. It works mainly through cholinergic fibers and reduces the activity of cardiac muscle, while in smooth muscle it increases tone and contractility.

Autonomic Nervous System is divided in two main branches, the sympathetic and the parasympathetic nervous system. The sympathetic system activates the body for action, it increases heart rate, breathing, and energy output. The parasympathetic system brings the body back to rest, it slows the heart, supports digestion, and restores balance.

It is known as the “rest and digest” response and leads to clear changes in the body:

• Decrease in stress hormone levels
• Slower heart rate, with reduced blood flow to muscles
• Slower breathing due to lower oxygen demand
• Increased blood flow to the digestive system
• Pupils constrict
• Organs return to regular maintenance functions

In this system, acetylcholine is the main neurotransmitter, released by both preganglionic and postganglionic fibers. It binds to nicotinic receptors in the ganglia and to muscarinic receptors in the target tissues. Structurally, it includes preganglionic and postganglionic fibers connected through ganglia. Preganglionic fibers are long, while postganglionic fibers are short.

The parasympathetic nervous system, PNS, supports relaxation and recovery. It works through acetylcholine, slows the heart rate, reduces stress hormones, and shifts the body toward digestion and restoration, while increasing tone in smooth muscle. This state creates the conditions for release and regulation in the body, which is why, during somatic shaking, parasympathetic activation often follows or alternates with activation phases, allowing the system to settle, integrate, and return to balance.