Neurons are nerve cells and the basic building blocks of our entire nervous systems. The neurons act as sensors for all types of stimuli and communicate the stimuli throughout the body. For example, neurons communicate to the brain that you should not leave your hand on a hot stove. In addition, the neurons are composed of 3 main components, the axon (the tail), the soma (the body), and the dendrites (the branch-like arms that stem from the soma).
You can see an example of a neuron at: http://www.alleydog.com/images/2neurons.gif