Which division has a single preganglionic neurons with many axon collaterals that forms 20 or more synapses with postganglionic neurons? sympathetic motor division?

The sympathetic division of the Autonomic Nervous System. The ganglia and synapses within that division are responsible for delivering information to the body regarding stress and impending danger. This is more commonly known as the fight-or-flight response.

Mg is used to measure mass