The nervous system is the body's communication system. It sends information to and from the brain and allows the control of the rest of the body in response. The nervous system is divided into two parts: the central nervous system, which consists of the brain and the spinal cord; and the peripheral nervous system.
The peripheral nervous system is the part of the nervous system that extends out from the brain and spinal cord to the rest of the body. Carrying motor and sensory information, it controls voluntary as well as involuntary behaviors and actions in the body.
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.
EXAMPLEWhen 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:
EXAMPLEWhen 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.
The parasympathetic branch of the autonomic nervous system:
EXAMPLESuppose 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.
Source: This work is adapted from Sophia author Erick Taggart.