On the other hand, if we are examining a collection or a group of cell bodies a group of neurons inside the peripheral nervous system this is known as a ganglia. So ganglia are those cells inside our peripheral nervous system and nucleus refers to our groups of neurons inside the central nervous system. Now, what about the pre ganglionic neuron and the post ganglionic neurons? So these are the two types of neurons that exist within the autonomic nervous system. So in the autonomic division of the peripheral nervous system the neurons that begin at the central nervous system the brain or the spinal cord and extend into the ganglia of our peripheral nervous system remember, the ganglia are simply the groups of cell bodies found inside the peripheral nervous system. These types of cells are known as pre ganglionic neurons.