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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 central nervous system (CNS) 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.
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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.
EXAMPLE
The 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.
The peripheral nervous system is divided into two parts:
The somatic nervous system includes all of the nerves that connect to the sense organs and the skeletal muscles within the body. It controls all of the voluntary behavior and the motor neurons, which help to move the body. These motor neurons allow for actions like drawing, jumping, running, and anything that we control directly.
Motor neurons can also control involuntary reactions, those called the reflex arc, which are simple, automatic responses to stimuli in the world.
EXAMPLE
When you go to the doctor's office and they hit your knee to see if your knee reacts very quickly, it's not an action that you necessarily control. The stimuli, the hitting of the knee, sends a reaction—not directly to your brain, but rather just to your spinal cord. The spinal cord is where reflex arcs are controlled. Then, that response is sent right back to your leg more quickly than if it had to go directly to your brain, and this is what allows your knee to give a quick, reflexive jerk.Sensory neurons are also controlled in the somatic system, which is responsible for smell, taste, sight, as well as the skin for touch. As you can see, the somatic system covers quite a lot of ground.
The autonomic nervous system includes all of the nerves within the rest of the body that connect to the internal organs. They control all of the internal involuntary body functions like breathing, which we can control voluntarily but that generally is something that we do automatically, outside of our control. These nerves also control functions like heart rate and digestion.
The autonomic nervous system is further subdivided into two different parts:
The sympathetic nervous system controls any body responses that are related to fight or flight. This is a protective response that kicks in when you feel like you're in danger.
The sympathetic branch of the autonomic nervous system is responsible for the following responses:
EXAMPLE
When you feel threatened, perhaps your heart beats faster or your palms sweat. This is a result of the sympathetic nervous system. Sometimes, people get so excited that they might throw up or accidentally urinate themselves. This is also the sympathetic nervous system in action.While the sympathetic nervous system excites the body, the parasympathetic nervous system keeps it at a normal level. It decreases the body from an excited state to a lesser level and helps to maintain the body after the danger has passed.
The parasympathetic branch of the autonomic nervous system:
EXAMPLE
Suppose someone is driving too close behind you and honking the horn. Once they turn off, you take a deep breath and your hands are no longer sweaty. This is a result of the parasympathetic nervous system.
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