Neurotransmitter Usage - ANS Parasymp. vs Symp


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7+ Year Member
Jan 26, 2011
  1. Medical Student
So we know that the somatic nervous system uses acetylcholine as its neurotransmitter. We also know that all preganglionic neurons of the ANS use acetylcholine....also the postganglionic neuron of the parasympathetic. The difference is the postganglionic fibers of the sympathetic neuron. It uses N or NE (adrenergic).

The thing I see in common with somatic and parasympathetic is that they synapse close to their effector whereas sympathetic postganglionic neurons lie far away from their effector (relatively speaking).

In the grand scheme of things, does NT usage depend on the proximity to the effector? Perhaps acetylcholine has a shorter half-life than epinephrine and must be used only when synapsing close to the effector? I am beginning my neuro study for the MCAT and just thought I would ask. Thanks.
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5+ Year Member
Jan 28, 2008
  1. Pre-Medical
The length between the axon terminal and its target (synaptic cleft) is the same for pretty much throughout the nervous system.

Sympathetic preganglionic neurons referred to as "short" meaning travel a short distance to their target sympathetic postganglionic neurons. Therefore, sympathetic postganglionic neurons are "long" meaning that their axons are travel a long distance in order to synapse with its effectors.

In contrast, the parasympathetic system is the opposite: long axons in preganglionic neurons and short axons in postganglionic neurons.

This website has an adequate diagram of the two systems.

Regardless of the which system, the length of the synapses are the same. Why a neuron uses Ach or NE is beyond the scope of the MCAT.
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