The neurons in all five have axons and dendrites. Synaptic complexity accounts for individual differences in ability. All five communicate through the synapse. Neurotransmitters are similar in all five. Neurons all receive, store, and transmit impulses.
Hormonal relationships are similar.
The brains of all five are immature at birth. Brain development differs by sex for all five. Most of what we know about the human nervous system originated in animal research.