Your nervous system is a network that sends signals between your brain and other parts of your body to control your body's movements and processes. This system includes your brain, spinal cord, and nerves. Your parasympathetic nervous system (PSNS) is one part of your nervous system, and it helps calm your body down.
When you're on edge after a stressful or dangerous situation, and your heart is beating quickly, for example, your PSNS is what helps your body relax and slow down.
What Is the PSNS?
The PSNS helps your body relax and maintains some of your body's functions, like digestion, heart rate, and breathing. It's a network of small neurons and large nerves that run throughout your body and regulate these processes.
Your PSNS is part of the autonomic nervous system, which connects your brain to most of your internal organs. Your autonomic nervous system controls body systems and processes that you don’t control consciously. For example, it produces the feeling of hunger when you need food and the feeling of panic when you're in danger. It also regulates the ways that many of your internal organs respond to certain conditions.
Your autonomic nervous system includes three subsystems: the PSNS, the sympathetic nervous system, and the enteric nervous system. The first two involve many processes throughout your body, and they complement each other. The enteric nervous system is within your gastrointestinal tract.
Sympathetic vs. PSNS
You've probably heard the phrase "fight or flight" to describe the body's response to an extreme, acute stressor. Your sympathetic nervous system automatically kicks your body into high gear when you need to defend yourself or run from a real or perceived threat.
Have you ever wondered how the body calms down after an experience like this? It's the PSNS, which helps your body relax and reduce activity.
The PSNS balances out the sympathetic nervous system. If the PSNS didn't exist, the sympathetic nervous system would take over during times of stress — and your body would not have a way of turning off its dramatic response.
The PSNS controls your body's "rest and digest" functions. It plays a large part in regulating digestion, heart rate, and breathing, for example.
What Does the PSNS Do?
The PSNS helps your body relax, conserve energy, and recover. It's responsible for various functions of your internal organs, such as their ability to relax, constrict (or narrow), and produce mucus.
Here are some of the things the PSNS does in different areas of your body:
Heart. When your heart rate is elevated from your body being under stress or from physical exercise, the PSNS slows your heart rate.
Lungs. While the sympathetic nervous system speeds up your breathing rate, the PSNS slows it down and causes your airways to constrict. Sometimes this constriction is helpful — but for people with asthma, this effect can be exaggerated, causing an extreme reaction to triggers like cold air. The PSNS also regulates mucus secretions in your lungs, which help you stay healthy by trapping irritants.
Digestion. Through its vast network of nerves, the PSNS aids in digestion as it helps the bowel muscles contract and push food through the small and large intestines. It helps your body poop and pee.
Eyes. The PSNS constricts your pupils and allows you to see close-up objects clearly. It also helps your eyes produce tears.
Sexual function. The PSNS affects sexual arousal, including erections in people with a penis and fluids that provide lubrication in people with a vagina.
Parasympathetic Nerves
Twelve pairs of nerves called "cranial nerves" (CNs) are attached to your brain. Each pair splits to both sides of your body, and these nerves are involved in processing senses like smell, taste, and touch. They also assist in facial movement and signaling between your brain and your head, neck, and the upper part of your chest and arms.
Four of these CNs belong to the PSNS. They are the oculomotor, facial, glossopharyngeal, and vagus nerves. These nerves are numbered using Roman numerals.
Oculomotor nerve (CN III)
The third nerve, the oculomotor nerve, helps you open and move your eyes. It also constricts your pupils, which helps your eyes focus on things that are close up.
Facial nerve (CN VII)
This nerve controls the muscles that you use to make facial expressions, and it's responsible for part of your sense of taste and your saliva production.
Glossopharyngeal nerve (CN IX)
Like the facial nerve, the glossopharyngeal nerve is responsible for part of your sense of taste and your saliva production. It also controls the muscles you use to swallow and helps regulate your blood pressure.
Vagus nerve (CN X)
The 10th CN, called the vagus nerve or vagal nerves, is the main nerve in your PSNS. It includes almost 75% of the nerve fibers in the PSNS. The vagus nerve regulates several processes and functions, including your blood pressure, heart rate, digestion, breathing, immune system, and mood.
The vagus nerve is the largest CN, going down each side of your body from your brain to your digestive tract. It connects with or passes through your neck, heart, lungs, and abdomen.
The vagus nerve connects your brain and your gut, and it sends signals back and forth — this is called the "brain-gut connection." Several conditions, such as posttraumatic stress disorder (PTSD), depression, and inflammatory bowel disease, may involve this brain-gut connection. Treatment for some of these conditions may include stimulating the vagus nerve through electrical impulses.
Signs of PSNS Dysfunction
A few telltale signs can suggest that your PSNS isn't functioning correctly. You might notice PSNS effects in the following physical and mental areas:
- Anxiety disorders, panic attacks, or PTSD
- Irritable bowel syndrome or an inflammatory disorder that affects the digestive tract
- Asthma and raised mucus in the nose
- Heart rate issues like palpitations or an irregular heartbeat
- Sexual problems (usually erectile dysfunction)
What Conditions Affect the PSNS?
Some specific conditions can affect your PSNS.
Nerve or brain trauma. Getting injured or experiencing physical nerve damage can affect the PNS. If you've hurt your spinal cord or sustained a blow to the head, you may see a neurologist to discuss potential damage to your nervous system. Be sure to seek emergency care as soon as possible after a back or head injury.
Autonomic neuropathy. This condition can be the result of bacterial or viral infections, but it's most often caused by type 2 diabetes. Symptoms include low blood pressure when standing, low blood sugar without shakiness and other common signs, exercise issues, and digestion problems such as bloating, constipation, diarrhea, and heartburn.
Multiple system atrophy. This is a brain condition that has neurological symptoms similar to Parkinson's disease. You may first notice movement problems and then your PSNS, or "automatic" bodily systems, will start malfunctioning.
It's important to see your doctor as soon as possible if you have trouble regulating your heartbeat, body temperature, or blood pressure. Not experiencing "danger" signals from your body means that you could be very ill without knowing it.
How Can You Keep the PSNS Healthy?
Your PSNS is a vital part of many bodily processes. Taking a multifaceted approach that combines stress reduction and beneficial lifestyle habits can help keep your PSNS healthy. Think about integrating the following lifestyle changes and precautions into your daily life to keep your peripheral nervous system functioning as it should:
- Eat a well-balanced diet, including making sure that you're getting enough vitamin B12. But it's also important not to take too much of certain vitamins.
- Get enough high-quality sleep. Your PSNS is at work while you're asleep.
- Exercise, but when you do, try to include a warm-up and cool-down, so your heart rate doesn't raise or drop too rapidly.
- Don't use substances like alcohol to self-medicate anxiety.
- Try to reduce your stress. Activities like practicing mindfulness, meditation, and yoga may help.
- Avoid dangerous activities that could cause accidents and nerve damage, and protect yourself from injury.
- Get screened for diabetes regularly and maintain a healthy lifestyle to avoid developing it. Diabetes can damage your nerves.
Because the PSNS helps regulate and control so many bodily systems, it's important to visit your doctor if you notice any symptoms that signal nervous system trouble, such as constipation and a rapid heart rate even when you're at rest. If you have a medical condition or disease, ask your doctor for information and resources about how this fascinating and complex part of your nervous system may be involved in your condition.
Takeaways
Your PSNS helps your body calm down after your sympathetic nervous system puts you in "fight or flight" mode. It also helps control many bodily processes that happen unconsciously, like digestion. The vagus nerve is the largest part of your PSNS, going from your brain to your digestive tract. Several healthy lifestyle habits, like exercise, can help keep your PSNS working smoothly.
PSNS FAQs
How does the PSNS affect stress?
The PSNS helps your body calm down after a perceived danger or a stressful situation, so it can help reduce stress.
What are the main components of the PSNS?
A large nerve called the vagus nerve makes up about 75% of your PSNS, but it also includes other nerves, and they connect to different organs throughout your body.
How is the PSNS activated?
You can activate your PSNS through activities like meditation, deep breathing, and exercise.
