Question

What substances do the neurotransmitters in the sympathetic nervous system contain at the first and second synapses?

Answer 1

Preganglionic neurons of the sympathetic nervous
system release acetylcholine while the postganglionic
neurons release norepinephrine.

Explanation:

Excellent resource and graphics here:
https://www.triton.edu/uploadedFiles/Content/Resources_and_Services/Services/Academic_Success_Center/Student_Resources/Nervous_System.pdf

The sympathetic nervous system is used in fight
or flight situations

A sensory pathway is divided into three sections.
First order neuron – carries the sensory impulse from
the sensory receptor to the central nervous system.

Second order neuron – carries the information from
the central nervous system to the thalamus.

Information traveling along second order neurons
deccussates from one side of the CNS to the other side
of the CNS.

Third order neuron – carries sensory information from
the thalamus to the cerebral cortex.

See also:
http://www.cerebromente.org.br/n12/fundamentos/neurotransmissores/neurotransmitters2.html

For good animations and chemical processes involved and a list of the 60+ specific neurotransmitters involved in the Nervous System.
Neurotransmitters are chemicals made by neurons and used by them to transmit signals to the other neurons