Parasympathetic nervous system

German: Parasympathikus
Greek: para - against, contrary to; sympathikos - involvement

1 Definition

The parasympathetic is the antagonist of the sympathetic in the autonomous nervous. It affects functions of the body for regeneration and metabolism for saving energy (trophotropic).Furthermore it tends to create homoiostasis again.

2 Anatomy

The nucleus of the parasympathetic nervous system lies in the brain stem and sacral part of spinal cord. The cranial nerves III(Nervus oculomotorius), VII (Nervus facialis), IX (Nervus glossopharyngeus) and especially X (Nervus vagus) contain parasympathetic fibers, which innervate muscles and glands of the head and neck. The cranial nerve V (Nervus trigeminus) has parasympathetic fibers in some parts, but they originate from Nervus facialis. The inner organs of the thorax and some of the abdomen are innervated by the nervus vagus.
Beside these there are so-called Nervi splanchnici pelvic (Nn. erigentes), which originate from segements S1-S3 of the sacral spinal cord. They affect the aboral part of the colon (behind the left colic flexure) and the structures in the lesser pelvis (eg the urinary bladder).

3 Physiology

Parasympathetic nerves use acetylcholine as pre- and postsynaptic neurotransmitter. It affects the so-called mAChR (muscarine acetylcholine receptors).
==Organotropic effect==

• Heart: negative chronotropic and dromotropic
• Blood vessels: no proof of direct effect
• Genital area: vasodilation (indirect by inihibition of sympathetic)
• Bronchia: constriction, increased production of mucus
• GI tract: increased secretion by glands, increased peristalsis
• Urinary bladder: contraction of Musculus detrusor vesicae, atony of sphincter
• Uterus: contraction
• Eye: constriction of Musculus sphincter papillae whit resulting miosis, constriction of Musculus ciliaris with increased accommodation
• Salivary glands: increased secretion
  

4 Pharmacology

• Medications, which increase the effect of the parasympathetic are called parasympathicomimetics. There are direct ones ( eg acetylcholine, pilocarpin, muscarin, arecolin) which affect acetylcholine receptors and indirect ones which inihibit acetylcholinesterase (examples: physostigmin, neostigmin, pyridostigmin).
• Medications that inihibit the parasympathetic are called parasympathicolytics (eg atropine, scopolamine, tropicamid and its derivates).