Parasympathetic

The parasympathetic system, the other half of the autonomic nervous system, is structured differently to the sympathetic system.

In some ways it is far more simple (thankfully) to understand as postganglionic neurones use acetlycholine 100% of the time to bring about their effect and in most cases has a inhibitory effect. At least this system isn't attempting to confuse us!

The parasympathetic preganglionic neurones (mouthful!) stem from the top of the CNS (brainstem) and from S2 - S4 in the pelvis. More specifically in the brain the nerves involved are the cranial nerves 3 (III), 7 (VII), 9 (IX) and to some extent 10 (X - who uses roman numerals these days?).
Now we can all recite that well known mnemonic (yes i had to look up how to spell that!). For those that can't be bothered here is the four involved:
3 - Oculomotor
7 - Facial
9 - Glossopharyngeal
10 - Vagus

Anyway, the preganglionic neurones travel all the way to just outside the organ they intend to effect and then synapse with a parasympathetic ganlgion. This therefore makes the postganglionic neurones of the parasympathetic nervous system very short. Because of the way this is structured you could say that the parasympathetic nervous system delivered signals ever so slighlty more quickly than the sympathetic nervous system (10 points for the theory here... ok its because of myelin distribute between postganglionic and preganglionic neurones). However it is ever so insignificant its probably not worth mentioning!

More soonish..