Sympathetic and Parasympathetic Nerve Fibres | Pharmacology

This article will help you to differentiate between sympathetic and parasympathetic nerve fibres.

Difference # Sympathetic Nerve Fibre:

1. They arise from thoraco-lumber (T₁ to L₃) region of the spinal cord.

2. Ganglia are nearer to CNS. The ratio of pre and postganglionic fibres is generally 1: 20 or more. So, the post ganglionic fibers are longer.

3. Neurotransmitters are ACh (in ganglia) and norepinephrine (at neuro-effector junc­tions).

4. Sympathetic activity increases in stress and emergency.

Difference # Parasympathetic Nerve Fibre:

1. They arise from the craniosacral (III, VII, IX, X, S₂ – S₄) region of the CNS.

2. Ganglia are away from CNS, and on or close to the organs. The ratio is gener­ally 1: 1. So, the postganglionic fibres are shorter.

3. Neurotransmitters are ACh in both the ganglia and nouro-effector junctions.

4. Parasympathetic activity predominates during rest.

In most of the places (e.g., in smooth muscles of the gut, bladder, and heart) the sympathetic and parasympathetic systems produce opposite effects; but in some other organs only one system operates.

The sweat glands and most blood vessels, for example, have only a sympathetic innervation and the ciliary muscle of the eye has only a parasympathetic innervation. On the other hand, the two systems may produce similar, rather than opposite effects in an organ (e.g., salivary glands).