Parasympathetic control of smooth muscle

The parasympathetic nervous system is the part of the autonomic nervous system that prepares the “relaxation response” in the body. It is mainly formed by cholinergic fibers and tends to increase the tone and contractility of smooth muscle.

It consists of preganglionic and postganglionic fibers, both connected in the ganglia. The preganglionic fibers are long, while the postganglionic ones are short.

Figure 1: Schematic representation of smooth muscle parasympathetic control. There is only one neurotransmitter released in the parasympathetic nervous system: 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.