What is the Parasympathetic Nervous System?

There is a lot of information available about the autonomic nervous system and how dysregulation can affect the body. There are two main branches of the autonomic nervous system: the parasympathetic and sympathetic. The sympathetic is often commonly referred to as the “fight or flight” system, and the parasympathetic is referred to as the “rest and digest” system. It’s normal for humans to flip between the sympathetic and parasympathetic nervous system at multiple points during the day. 

What Is The Main Function of The Parasympathetic Nervous System?

The overall function of the parasympathetic nervous system is to regulate the unconscious functions of digestion, defecation, urination, lacrimation, and salivation. Basically it helps with the body resting, repairing, and digesting. The vagal nerves are the main nerves of the parasympathetic nervous system. The vagus nerve can be stimulated to help stimulate digestive hormones and secrete stomach acid. When the vagus nerve is stimulated, heart rate decreases.

The parasympathetic nervous system calms the body down and returns it to a resting state after a stressful situation. When the body is alarmed, it goes into a sympathetic state of fight-or-flight. When the stressor is over, the parasympathetic system is stimulated, and you can notice some of the following symptoms:

  • Pupil constriction
  • Decreased blood pressure and heart rate
  • Bronchial muscle constriction
  • Digestion increase
  • Mucus and saliva increased production
  • Increased output of urine

The parasympathetic nervous system’s responsibility includes food digestion, assimilation, and building energy for the body. Its goal is to restore a level of homeostasis in the body and is active when the body is recuperating and resting. Some people can get stuck in parasympathetic override, which can contribute to loss of motivation, lethargy, and depression. 

What Is An Example of A Parasympathetic Nervous System?

The parasympathetic nervous system begins in the brain and extends out through long fibers that connect with unique neurons near the organ they are intended to act on. As the parasympathetic nervous system signals to hit these neurons, they travel a short distance to their respective organs. An example of parasympathetic nervous system includes areas that the parasympathetic nervous system like:

  • Eyes 
  • Lacrimal glands (they produce tears)
  • Parotid glands (that produce saliva)
  • Salivary glands (also produce saliva)
  • Nerves that lead to the trunk and stomach 
  • Nerves that lead to the bladder
  • Blood vessels and nerves responsible for a male’s erection

The parasympathetic nervous system is what keeps your body running at optimal health. It directs the body to keep the basic functions operating as they should. There are numerous special receptors for the parasympathetic nervous system in your heart called muscarinic receptors. The receptors work hard to help keep your body from getting into the sympathetic nervous system. They also help keep your resting heart rate at a normal level, generally between 60 and 100 beats per minute. 

According to studies, a person’s resting heart rate can be one indicator of how well a person’s parasympathetic nervous system is working, specifically the vagus nerve. This only works when the person doesn’t take medications that alter or affect heart rate, like beta-blockers, or underlying medical conditions that affect the heart. Heart failure actually reduces the response of the parasympathetic nervous system, resulting in increased heart rate. 

What Is The Difference Between Sympathetic and Parasympathetic?

When the body is operating in the parasympathetic state, the body’s energy goes towards repairing and renewing the body. If the body is in a sympathetic state, the body’s energy goes towards keeping the human alive, as it believes there is a threat. For example, if someone scares you, your body can go to the sympathetic state and be on high alert as if a tiger was chasing you. The sympathetic and parasympathetic nervous systems are complete opposites, and it’s important to find a good balance. 

Some of the functions of the parasympathetic nervous system include:

  • Maintains homeostasis in the body and allows the rest and digest response
  • Aims to balance the body to a natural calm state
  • Has a slower response time due to comparatively longer neuronal pathways
  • Relaxes muscles and reduces heartbeat
  • Contracts the pupil, making it smaller
  • Increases saliva and digestion

Some of the functions of the sympathetic nervous system include:

  • Stimulating fight or flight response
  • Prepares the body for any potential danger
  • Faster response time due to shorter neuronal pathways
  • Tense muscles and increased heartbeat
  • Dilated pupils to let in more light
  • Inhibited saliva secretion
  • Adrenal glands release adrenaline, and more glycogen is converted to glucose

There are many things you can do to help stimulate the parasympathetic response in your body. Meditation, breath-work, and neural retraining programs are all helpful in getting the body into the rest and digest mode. Massage is a very popular way to get the body into the parasympathetic nervous system. 

What Happens When The Parasympathetic Nervous System Is Activated?

When you have an activated system, you may notice slower heart and breathing rates, better digestion, and lower blood pressure. As the body enters into a state of relaxation, the relaxation can lead to recovery. The more time a body spends in a parasympathetic state, the healthier it is. What are some things you can do to get the body into a parasympathetic state?

  • Reduce stress as much as possible. With less stress, the body has a better chance to relax and rest. If your life is highly stressful, you can change how you respond to stress, which can help your overall quality of life. 
  • Meditate regularly. Meditation can help get the brain into a calm state, allowing your body to work on healing. Meditation can help so many different ailments as it slows your heart and breathing rates. 
  • Get a regular massage. Massage helps us feel stronger, calmer, and can also help the body fight infections. 
  • Breath work. By consciously being aware of your breathing and breath rates, you can help get your body into a parasympathetic state. When you take slow and deep breaths, it sends a message to your body that it is safe and all is well. 
  • Yoga. Yoga can help decrease the fight or flight response and train your body and brain to operate in a calmer state. 
  • Get good quality sleep. By getting enough and good quality sleep, the body has a chance to rest and recover. When your body doesn’t have enough sleep, it can trigger the sympathetic nervous system. 

There is a delicate balance between the parasympathetic and sympathetic nervous system. By being consciously aware of how your body responds to stressful situations, you can help support it into a state of homeostasis. Using the tools above, you can help keep your body in a calm and relaxed state, helping to promote health and wellness.

Why Is It Called The Parasympathetic Nervous System?

The parasympathetic nervous system is often commonly referred to as the rest and digest system. If you’re trying to remember which system is which, you can make the distinction between the two by remembering the first letter of each of them. The sympathetic nervous system starts during times of high stress, and the parasympathetic nervous system is what is operating during times of peace. 

When the parasympathetic nervous system shuts down and the sympathetic nervous system is activated, the energy that the body was spending on processes like digestion and healing are paused. That energy is then diverted to keeping the body alive, as the sympathetic nervous system has shown that there is a threat. When the threat is over, the body should leave sympathetic mode and return to parasympathetic mode. 

Where Are Parasympathetic Nerves Located?

The parasympathetic nervous system is made up of many pathways that connect the craniosacral components to the peripheral tissues. Each of the parasympathetic pathways contains two neurons: the synaptic (preganglionic) and postsynaptic (postganglionic) neurons. They are connected by the axons of the presynaptic neurons. 

Presynaptic neurons are located within the medulla oblongata and sacral spinal cord. There are presynaptic fibers called axons that leave the CNS and move towards the postsynaptic neurons. Using acetylcholine as a neurotransmitter, the parasympathetic nervous system is often referred to as the cholinergic pathways. The location of the parasympathetic nerves of the head and neck are found in the medulla oblongata, and the presynaptic parasympathetic neurons of the thorax, abdomen, and pelvis are located in the sacral segments of the spinal cord.