In certain autoimmune diseases (where your body’s immune system begins to attack itself), such as Guillain-Barre syndrome or Miller Fisher syndrome, the brain and spinal cord are spared, but many of the nerves in the peripheral nervous system are affected. But what exactly is meant by the peripheral nervous system and what does it do?
Most people think of the human nervous system as being made up of the brain and spinal cord. And that’s true, up to a point. You see, your brain and spinal cord make up what is known as your central nervous system (CNS) but that is only half of the picture. Let’s look a little closer at the anatomy (and don’t worry, there won’t be a test!)
Central Nervous System
Brain & Spinal Cord
Peripheral Nervous System
Peripheral Nervous System – Controlling Our Muscles & Lungs
The other, almost invisible part of your nervous system is known as the peripheral (meaning ‘on the periphery’ or away from the center) nervous system or the PNS and is made up of nerves that come out of the lower part of the brain, nerves that come out of the spinal cord, plus a very large nerve known as the vagus, which has numerous fibers connecting to the heart, lungs, gut, and many other organs. The PNS is divided into two different parts with two different functions: the somatic nervous system and the autonomic (automatic) nervous system.
Controls our muscles.
Controls our lungs, heart, and other organs we do not have to think about.
The somatic (from the Latin word ‘soma’ meaning body) is that part of your peripheral nervous system that sends nerves from the brain and spinal cord out to your muscles. The somatic system is under your voluntary control, as when for example, you want to move your arms and legs. The autonomic nervous system, on the other hand, operates for the most part, outside of your conscious awareness. This system in turn is also divided into two subsystems: the sympathetic and the parasympathetic nervous systems.
Here’s how to think about these two systems:
Sympathetic – Fight or Flight
Your sympathetic nervous system gets your body ready for vigorous physical action, when you are confronted with a wild animal running toward you for example, and is often referred to as the fight-or-flight response. So it would make sense that this system works to increase your heart rate (pumping more blood), increase your breathing rate (so you can take in more oxygen), widen the pupils of your eyes (so they can take in more light and you can see better), narrow your blood vessels (so you are less likely to bleed to death if you are hurt) and decrease your gut activity (you don’t need to be bothered with digesting lunch if you are running away from a threat) among other responses.
Parasympathetic – Rest and Digest
In contrast, your parasympathetic system tends to kick into gear when you are out of danger and so slows down your heart rate, increases the action of your gut, turns on saliva flow and so forth. This system is known as the rest-and-digest system.
The important thing to remember about these two systems is that the threat can be real or it can be imagined. Remember the last time you were somewhere and it was dark and you heard a weird noise that you couldn’t immediately identify? Most likely, your heart began thumping, you began to breath faster and you suddenly forgot all about that nice dessert that was waiting on you in the kitchen.
The threat might have been real (a home invader trying to break in) or it could have been imagined (the noise was just a tree branch scraping against a window in the wind.) The thing to get is this: your body reacts the same, whether the threat is real or imagined. And this goes for worrying about things that might happen in the future as well, as it keeps your body in a continuous low level state of fight-or-flight. This is not good for your health.Fortunately, there are some things you can do to activate your parasympathetic system to override the sympathetic response, such as purposefully slowing down your breathing or visualizing yourself in a peaceful, calm natural area such as on the beach or in the mountains.
Hopefully now you have a better appreciation of your marvelous nervous system, its parts and how it works to regulate your internal state to protect you from harm.