The nervous system is the body's communication system. It sends information to and from the brain and allows it to control the rest of the body and its actions. It is made up of individual neurons, which are the cells that transmit information within the nervous system.
The nervous system consists of two systems:
The first--and most important---part of the nervous system is the central nervous system (CNS). This is the area of the body which acts as the control center for the rest of the nervous system. It collects information from the rest of the body and everything outside of it, then sends out information and causes the body's various responses.
The most recognizable part of the central nervous system is the brain. The brain is housed inside of your head and is the central processing unit of the nervous system and the rest of the body.
The CNS is where everything that we think of as being a person and being human is housed. All of the things that involve personality and mental states in thinking and deciding and planning--all of those things are housed directly within the brain. As you can see, it's the most important thing in psychology, and the most important organ in the body.
The other main part of the central nervous system is the spinal cord, which is a thick bundle of neurons that connects directly to the brain and runs along your back. This is also where you'll find the vertebrae, which protect the spinal cord.
When the spinal cord is damaged, it can lead to paralysis of different parts of the body. Because it acts as a conductor for all of this information, if a certain part is damaged, then none of those messages can be sent to the corresponding parts of the body.
The spinal cord also acts as a control for certain reflexes, which don't go directly to the brain, but rather simply go to the spinal cord and cause a quick involuntary response by the body.
The second part of the nervous system is the peripheral nervous system (PNS). The PNS essentially includes the rest of the neurons that are within the body--everything outside of the brain and spinal cord.
The peripheral nervous system acts to control muscles and to carry sensory information from the outside world. It also controls involuntary behaviors, like the functioning of our organs.
EXAMPLEThe peripheral nervous system tells your stomach when to digest and when to grumble, as well as telling your heart how to beat.
The PNS also controls involuntary reactions. Sweating, for example, is a result of the PNS responding to the outside environment.
Source: This work is adapted from Sophia author Erick Taggart.