Parasympathetic nervous system postganglionic fibers

In contrast, the parasympathetic nervous system(PNS) is our vegetative system, that is, it controls automatic processes such as digestion. Its main purposes are energy conservation and restoration. The preganglionic fibers in the PNS are long and the postganglionic are short. The ratio of pre- to post- is low which means the PNS is not as diffuse as the SNS. 

Acetylcholine is the endogenous neurotransmitter of the parasympathetic nervous system. The parasympathetic nerve fibers are found in both the autonomic and central nervous systems. These fibers are classified into those that are stimulated by muscarine and those that are stimulated by nicotine. Nicotine, an alkaloid Uom Nicotiana tabacum, stimulates preganglionic fibers in both the parasympathetic and sympathetic systems as well as the somatic motor fibers of the skeletal system. Muscarine, an alkaloid from the poisonous mushroom Amanita muscaria, stimulates postganglionic parasympathetic fibers with receptors found on autonomic effector... 

Summary of the neurotransmitters released and the types of receptors found within the autonomic and somatic nervous systems. [Note This schematic diagram does not show that the parasympathetic ganglia are close to or on the surface of the effector organs and that the postganglionic fibers are usually shorter than the preganglionic fibers.]... 

D. The postganglionic fibers of the parasympathetic division are long, compared to those of the sympathetic nervous system. 

The autonomic nervous system guides the electrical and mechanical functions of the heart. The heart is innervated by both the sympathehc and parasympathetic systems, which have opposite effects and are activated reciprocally. They play important roles in arrhythmia susceptibility. Sympathetic shmulation originates from the intermediolateral column of the thoracic spinal cord. Its neurotransmitter, norepinephrine, is released from neurons of postganglionic fibers of stellate ganglia and epinephrine is released from the adrenal medulla. Both of these act on cardiac p-adrenergic receptors. Sympathetic nerves are predominantly on... 

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