MCAT Q

[RiPSTONE]

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So I recently read about the pre-ganglionic and post-ganglionic nerve fibers for the sympathetic and parasympathetic system, and I was wondering what's the reasoning behind the difference in the lengths of the two for the different systems (i.e. The pre-ganglionic nerve fiber is shorter in the sympathetic system). Also I was wondering why the sympathetic uses norepinephrine as its neurotransmitter rather than acetylcholine at both the pre- and post- for the parasympathetic. Thanks!

 

[orangetea]

So as far as the length of the preganglionic fibers go the reason the Sympathetic is shorter is because the sympathetic effects are fast and less precise(just think fight or flight) Those fibers need to be as close as they can be to spinal chord so the message is transmitted to effector organs ASAP. Parasympathetic on the other hand has a lot more time to direct messages to it's specific organs hence why the fibers can be longer.

I am not sure about the difference in neurotransmitters but I am sure google can help 🙂

 

[sillyjoe]

@orangetea has it right. It also has a lot to do with divergence. The sympathetic response needs to be an amplified response since it is used in times of danger/stress etc. Therefore, having sympathetic synapses at the paravertebral ganglia allows for many divergent signals (1 preganglionic fiber --> multiple postganlionic fibers) and thus an amplification-type response.

In contrast, parasympathetic responses are generally, "rest/digest/breed" and therefore, you want to minimize resources as well as have a much more targeted and efficient response at the end organ. Therefore, the parasympathetic preganglionic fibers tend to be longer having synapses very close to the effector organ.