Created: October 28, 2009; Last Update: August 19, 2016; Next update: 2022. Show
The nervous system is made up of all the nerve cells in your body. It is through the nervous system that we communicate with the outside world and, at the same time, many mechanisms inside our body are controlled. The nervous system takes in information through our senses, processes the information and triggers reactions, such as making your muscles move or causing you to feel pain. For example, if you touch a hot plate, you reflexively pull back your hand and your nerves simultaneously send pain signals to your brain. Metabolic processes are also controlled by the nervous system. There are many billions of nerve cells, also called neurons, in the nervous system. The brain alone has about 100 billion neurons in it. Each neuron has a cell body and various extensions. The shorter extensions (called dendrites) act like antennae: they receive signals from, for example, other neurons and pass them on to the cell body. The signals are then passed on via a long extension (the axon), which can be up to a meter long. The nervous system has two parts, called the central nervous system and the peripheral nervous system due to their location in the body. The central nervous system (CNS) includes the nerves in the brain and spinal cord. It is safely contained within the skull and vertebral canal of the spine. All of the other nerves in the body are part of the peripheral nervous system (PNS). Regardless of where they are in the body, a distinction can also be made between voluntary and involuntary nervous system. The voluntary nervous system (somatic nervous system) controls all the things that we are aware of and can consciously influence, such as moving our arms, legs and other parts of the body. The involuntary nervous system (vegetative or autonomic nervous system) regulates the processes in the body that we cannot consciously influence. It is constantly active, regulating things such as breathing, heart beat and metabolic processes. It does this by receiving signals from the brain and passing them on to the body. It can also send signals in the other direction – from the body to the brain – providing your brain with information about how full your bladder is or how quickly your heart is beating, for example. The involuntary nervous system can react quickly to changes, altering processes in the body to adapt. For instance, if your body gets too hot, your involuntary nervous system increases the blood circulation to your skin and makes you sweat more to cool your body down again. Both the central and peripheral nervous systems have voluntary and involuntary parts. However, whereas these two parts are closely linked in the central nervous system, they are usually separate in other areas of the body. The involuntary nervous system is made up of three parts:
The sympathetic and parasympathetic nervous systems usually do opposite things in the body. The sympathetic nervous system prepares your body for physical and mental activity. It makes your heart beat faster and stronger, opens your airways so you can breathe more easily, and inhibits digestion. The parasympathetic nervous system is responsible for bodily functions when we are at rest: it stimulates digestion, activates various metabolic processes and helps us to relax. But the sympathetic and parasympathetic nervous systems do not always work in opposite directions; they sometimes complement each other too. The enteric nervous system is a separate nervous system for the bowel, which, to a great extent, autonomously regulates bowel motility in digestion. Sources
Your parasympathetic nervous system is a network of nerves that relaxes your body after periods of stress or danger. It also helps run life-sustaining processes, like digestion, during times when you feel safe and relaxed. The informal descriptions for this system include the rhymes “rest and digest” or “feed and breed.”
Your parasympathetic nervous system is part of your autonomic nervous system. It could be called your “automatic” nervous system, as it’s responsible for many functions that you don’t have to think about to control. This can include control of your heart rate, blood pressure, digestion, urination and sweating, among other functions. The parasympathetic part of your autonomic nervous system balances your sympathetic nervous system. While your sympathetic nervous system controls your body’s “fight or flight” response, your parasympathetic nervous system helps to control your body’s response during times of rest.
Your parasympathetic nervous system’s job is usually to relax or reduce your body’s activities. Because of the signals it carries, the rhyming phrases “rest and digest” or “feed and breed” are easy ways to remember what your parasympathetic nervous system does. Your parasympathetic nervous system can have the following effects:
What’s the difference between the parasympathetic and sympathetic nervous systems?Your sympathetic and parasympathetic nervous systems have opposite but complementary roles. Your sympathetic nervous system carries signals that put your body’s systems on alert, and your parasympathetic carries signals that return those systems to their standard activity levels. Your sympathetic nervous system takes the lead when your safety and survival are at risk, but that system’s actions can strain body systems when it’s active for too long. Because these two systems offset each other, they help maintain balance in your body. Your parasympathetic nervous system also manages the activity in organs throughout your body when you feel calm and safe. These functions don’t involve risk or danger but are still key in keeping you alive and healthy.
Your parasympathetic nervous system is one of two parts of your autonomic nervous system. Your autonomic nervous system is a subsystem of your peripheral nervous system, which is all the nervous tissue in your body excluding your brain and spinal cord. Your parasympathetic nervous system uses four of your 12 cranial nerves. These are nerves that connect directly to your brain. Three of those four only involve your senses and glands connected to your eyes, nose and mouth. The fourth, your vagus nerve, connects to part of your mouth and also extends down through your neck to your chest and abdomen (belly). Your vagus nerve makes up about 75% of your parasympathetic nervous system overall, connecting to your heart, lungs and other vital internal organs. Farther down, 31 spinal nerves connect directly to your spinal cord, but your parasympathetic nervous system only uses some of them in the lower part of your spine. This sends signals to your bladder and bowels to relax so you can use the bathroom. What is it made of?Your parasympathetic nervous system’s components are similar to those found in other parts of your nervous system. Neurons are the main type of cell — they can generate and receive signals.
Many conditions and problems can affect your autonomic nervous system, including your parasympathetic nervous system. Potential problems include:
What are some common signs and symptoms of parasympathetic nervous system problems?Your parasympathetic nervous system controls processes in your body that should happen automatically. That means these problems usually get noticed when something doesn’t happen as expected. Possible symptoms include: What are some common tests to check parasympathetic nervous system functions?Potential tests include: What are the common treatments for parasympathetic nervous system conditions?Treating conditions that affect your parasympathetic nervous system is often challenging. That’s because the treatments can change dramatically, depending on what’s behind the problem. The treatments can also include many different approaches, ranging from medication to surgery. Sometimes, treatment of a parasympathetic nervous system problem requires treating or curing an underlying problem. In other cases, a condition isn’t curable, and the goal will be to treat and minimize the impact of symptoms.
Prevention can make all the difference in protecting and maintaining your parasympathetic nervous system. The best preventive measures include:
A note from Cleveland Clinic Your parasympathetic nervous system is a key part of your body’s long-term survival. This system constantly works without you thinking about it, whether you’re asleep or awake. It helps relax you in times of calm and provides a balance with your body’s short-term survival responses. While conditions that affect it are rare, protecting your parasympathetic nervous system is still important to your overall health and well-being.
Last reviewed by a Cleveland Clinic medical professional on 06/06/2022. References
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy |