When you are looking at biology and how it affects behavior you are looking at neurons as these are the base level of how the body communicates and form behavior. A neuron is the basic working unit of the nervous system (which includes the central and peripheral nervous system). The central nervous system (CNS) is comprised of the brain and spine and the peripheral nervous system (PNS) is comprised of nerves that are connected to every other part of the body. Behavior occurs within the body when neurons within the CNS send messages from the brain, down the spine, and to the PNS. This results in muscle movement, and automatic behaviors such as breathing. Information is taken from the PNS and is sent back through the spine to the brain where that information is processed and reactions and emotions are formed. Without the neuron firing within the CNS this sequence of events could not occur and behavior would not be possible.