Parasympathetic Nervous System (PSNS)

What is the parasympathetic nervous system?

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.

What does the parasympathetic nervous system do?

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:

• Eyes: It constricts your pupils to limit how much light enters your eyes. It also makes changes that can help improve your close-up vision, and causes tear production in your eyes.
• Nose and mouth: It makes glands in your mouth produce saliva, and glands in your nose produce mucus. This can be helpful with digestion and breathing during times of rest.
• Lungs: It tightens airway muscles and ultimately reduces the amount of work your lungs do during times of rest.
• Heart: It lowers your heart rate and the pumping force of your heart.
• Digestive tract: It increases your rate of digestion and diverts energy to help you digest food. It also tells your pancreas to make and release insulin, helping your body break down sugars into a form your cells can use.
• Waste removal: It relaxes the muscles that help you control when you pee (urinate) or poop (defecate).
• Reproductive system: It manages some of your body’s sexual functions, including feeling aroused (erections in people with a penis and secreting fluids that provide lubrication during sex in people with a vagina).

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.

Where is the parasympathetic nervous system located?

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.

What are the common conditions and disorders that affect the parasympathetic nervous system?

Many conditions and problems can affect your autonomic nervous system, including your parasympathetic nervous system. Potential problems include:

• Type 2 diabetes. Uncontrolled Type 2 diabetes can damage your autonomic nervous system, including your parasympathetic nervous system.
• Congenital and genetic conditions. These are disorders or conditions you have at birth. You have genetic conditions because you inherit them from one or both parents. Inherited forms of amyloidosis can cause parasympathetic nervous system problems.
• Parasympathetic nervous system problems can cause incontinence when there’s damage to the nerves that control your bladder and bowels.
• Multiple system atrophy. This severe condition is similar to Parkinson’s disease, damaging autonomic nerves over time.
• Sexual dysfunction. People with parasympathetic nervous system damage may have erectile dysfunction.
• Trauma. Nerve damage from injuries is potentially long-term or even permanent. This is especially the case when you have injuries to your spinal cord or main nerve structures that impair or cut off parasympathetic connections farther down.

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:

• Constipation.
• Fast heart rate (tachycardia) even when resting.
• Heart rhythm problems (including arrhythmias such as atrial fibrillation).
• Sexual dysfunction.
• Trouble digesting food (including gastroparesis).

What are some common tests to check parasympathetic nervous system functions?

Potential tests include:

• Blood tests (these can detect many problems, ranging from immune system problems to the levels of neurotransmitters in your blood).
• Electrocardiogram (EKG).
• Genetic testing.
• Magnetic resonance imaging (MRI).
• Sweat testing (including how much you sweat and seeing if there are places on your body where you don't sweat as you should).

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.

How can I prevent conditions and problems that affect the sympathetic nervous system?

Prevention can make all the difference in protecting and maintaining your parasympathetic nervous system. The best preventive measures include:

• Eat a balanced diet. Vitamin deficiencies, especially vitamin B12, can damage your nervous system. You should also avoid overusing vitamins (especially B6, which has toxic effects on your nervous systems at high levels).
• Avoid abusing drugs and alcohol. Substance use, including frequent heavy drinking, can have toxic effects and damage your sympathetic nervous system.
• Stay physically active and maintain a healthy weight. Type 2 diabetes damages your autonomic nerves over time. That’s why preventing it, or at least delaying when it starts, can make a big difference in your overall well-being.
• Wear safety equipment as needed. Safety equipment can be a big help if you want to prevent nerve damage from injuries, regardless of whether you use the equipment during work or play activities.
• Manage chronic conditions as recommended. If you have a chronic condition that can damage your nervous system, you should take steps to manage this condition. Your healthcare provider can help guide you on how to do that. That guidance can make a big difference in helping you limit the condition's progress or how it affects your life.

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.