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The sympathetic Nervous system is one half of the autonomic nervous sysetm.
The majority of it's effects are excitatory and therefore understandably the majority of the neurotransmitters used in the postganlionic synapses is noradrenaline. However there are a few cases where acetlycholine is use just to confuse you.
The autonomic nervous system neurones are divided into two identifiable sections. Preganglionic and Postganglionic - as the name suggests the neurones are either side of a autonomic ganglion! These autonomic ganglia run down either side of the spine in a structure known as the sympathetic trunk. The preganglionic neurones exit via the ventral root and synapse with the ganglia - the area seen macroscopically containing preganglionic neurones is known as the white rami communicantes because of the myelin present around the neurones (preganglionic autonomic neurones are a class B neurone).
The post ganglionic neurones of the sympathetic system then travel to the organ/structure they elicit their effect on and synapse with them. The macroscopic area you see containing post ganglionic neurones is the grey rami communicantes because of the lack of myelin around the neurones here (postganglionic autonomic neurones are a class C neurone).
There are a few ganglia that lie further away from the spine such as the coeliac ganglion - this is the ganlgion where as you would expect the sympathetic nervous system transmisses its signal to effect the stomach and duodenum.
The parasympathetic nervous system differs majorly in its structure.