Parasympathetic Nervous System

Last Updated: April 28, 2024

Parasympathetic Nervous System

The parasympathetic nervous system (PNS) is one of two main divisions of the autonomic nervous system, alongside the sympathetic nervous system (SNS). While the SNS prepares the body for “fight or flight” during stress, the PNS manages “rest and digest” functions, conserving energy and regulating processes like digestion and urination. This balance helps maintain bodily homeostasis and adapt to different situations.

Definition of Parasympathetic Nervous System

The parasympathetic nervous system is a division of the autonomic nervous system that is responsible for conserving energy and promoting a state of rest and digestion. It works to slow down the heart rate, increase intestinal and gland activity, and relax sphincter muscles in the gastrointestinal tract. This system is often referred to as the “rest and digest” system, in contrast to the sympathetic nervous system, which stimulates the body’s “fight or flight” responses.

Functions of the Parasympathetic Nervous System

The parasympathetic nervous system (PNS), also known as the “rest and digest” system, plays a crucial role in maintaining and restoring the body’s energy by managing various bodily functions during relaxed states. Below is an easy-to-understand breakdown of its primary functions:

  • Heart Rate and Blood Flow: The PNS reduces the heart rate and adjusts blood flow to different parts of the body, focusing on the digestive system and skin.
  • Digestive System: It stimulates digestion by increasing intestinal muscle contractions, which helps move food through the digestive tract. It also boosts activity in the stomach and intestines and enhances the secretion of digestive enzymes and saliva, which aid in breaking down food.
  • Eye Functions: In the eyes, the PNS activates to constrict the pupils and accommodate the lens for better near vision.
  • Respiratory Changes: In the lungs, the PNS prompts bronchial muscles to constrict, narrowing the airways slightly, which is typically a non-issue in a relaxed state.
  • Reproductive Organs: The system supports sexual arousal by promoting blood flow to the genital areas and facilitating erection in males.
  • Excretory and Urinary Functions: It aids in bladder control by contracting the bladder muscles and relaxing the sphincters, which allows for urination.

The PNS primarily uses acetylcholine as its neurotransmitter, which quickly acts on target organs through specific receptors known as muscarinic receptors. These receptors help initiate various bodily responses, depending on their location and the type of muscle or gland they influence. Once acetylcholine has completed its function, it is rapidly broken down by the enzyme acetylcholinesterase to prevent overstimulation and allow the body to return to a balanced state.

Examples of Parasympathetic Nervous System Functions

The parasympathetic nervous system (PNS) influences various bodily functions crucial for maintaining a state of relaxation and promoting recovery. Here are some examples of how the PNS impacts different systems and processes in the body:


  • Stimulation of Digestive Juices: The PNS increases the production of saliva, gastric juices, and enzymes, which are essential for breaking down food.
  • Enhanced Gastrointestinal Motility: It promotes the movement of muscles in the gastrointestinal tract to facilitate the smooth passage of food.


  • Bladder Muscle Contraction: The PNS helps in contracting the bladder muscles, making it easier to urinate.
  • Relaxation of Urinary Sphincters: It relaxes the sphincters in the urinary system, allowing urine to be expelled from the body.


  • Pupil Constriction: The PNS is responsible for constricting the pupils, which helps in adjusting the vision to varying light conditions.
  • Accommodation for Near Vision: It changes the shape of the lens in the eye to improve focus on nearby objects.


  • Rectal Contraction: The PNS aids in contracting the rectum, which is necessary for defecation.
  • Relaxation of Anal Sphincters: It also relaxes the anal sphincters to allow the passage of stool.


  • Stimulation of Tear Production: The PNS increases tear production, helping to lubricate and protect the eyes.

Meditation and Breathwork

  • Lowered Heart Rate: During meditation and breathwork, the PNS helps lower the heart rate, promoting relaxation and decreasing stress levels.
  • Deepened Breathing: It supports deeper and slower breathing, enhancing oxygen intake and promoting a calm state.


  • Decreased Heart Rate: The PNS reduces the heart rate, which conserves energy and aids in managing stress.


  • Bronchial Muscle Contraction: In the lungs, the PNS causes the bronchial muscles to contract slightly, which is generally not noticeable but important in high-stress situations.

Neurotransmitters of the Parasympathetic Nervous System

The parasympathetic nervous system plays a crucial role in maintaining your body’s rest and digest activities. It helps calm the body after stressful situations and ensures that the body’s energy is conserved. An essential part of how this system functions involves neurotransmitters, which are chemical messengers that transmit signals from nerve cells to target cells.

Acetylcholine: The Key Player

Acetylcholine stands out as the star neurotransmitter of the parasympathetic nervous system. It primarily handles the communication between nerves and muscles, and it also has significant roles in attention and memory in the brain. Here’s how it works:

  1. Transmission Initiation: When a nerve signal reaches the end of a nerve fiber, it prompts the release of acetylcholine.
  2. Signal Reception: Acetylcholine crosses the small gap between the nerve ending and the target cell, binds to specific receptors on the cell surface, and activates them.
  3. Muscle Movement or Secretion Stimulation: Depending on the target cell, the result can be muscle contraction (like slowing the heartbeat) or increased secretion of bodily fluids (like saliva or digestive juices).

How Acetylcholine Maintains Balance

Acetylcholine ensures the body remains in a state of balance after the fight or flight responses triggered by the sympathetic nervous system. By promoting relaxation, slower heart rate, and increased digestive activities, it helps the body conserve and restore energy. This balance is vital for long-term health and efficient bodily function.

The Breakdown Process

After acetylcholine does its job, it must be broken down to prevent continuous stimulation of the target cells, which could lead to excessive relaxation. The enzyme acetylcholinesterase is responsible for this, ensuring that acetylcholine’s effects are timely and appropriately limited.

Anatomy of the Parasympathetic Nervous System

The parasympathetic nervous system (PNS) is a key component of the autonomic nervous system, responsible for controlling the body’s rest and digest functions. It acts as a counterbalance to the sympathetic nervous system, which governs the body’s fight or flight responses.

Craniosacral Origin

The parasympathetic nervous system is often termed the “craniosacral system” because its nerves originate from specific areas in the brain and sacral spinal cord. Here’s a closer look at these origins:

  • Cranial Nerves: Several cranial nerves, including the oculomotor nerve (III), facial nerve (VII), glossopharyngeal nerve (IX), and vagus nerve (X), carry parasympathetic fibers. These nerves affect functions such as pupil constriction, saliva production, and control of various organs through the vagus nerve, which is notably extensive in its reach.
  • Sacral Spinal Cord: The sacral part of the PNS originates from the S2 to S4 sacral spinal segments. Nerves from this area innervate the lower part of the colon, rectum, bladder, and genital organs.

Parasympathetic Nervous System Disorders

The parasympathetic nervous system (PNS) is a crucial component of the autonomic nervous system, primarily responsible for the body’s rest and digest functions. It helps regulate bodily functions such as saliva production, urination, digestion, and slowing down the heartbeat. Disorders of the PNS can lead to a variety of symptoms and effects, impacting overall health and quality of life.

Common Disorders of the Parasympathetic Nervous System

  • Autonomic Neuropathy: This condition involves damage to the autonomic nerves, which affects the parasympathetic functions. It is often seen in people with diabetes and can lead to gastrointestinal, urinary, and cardiovascular issues.
  • Vasovagal Syncope: Triggered by long periods of standing or emotional stress, this condition causes a sudden drop in heart rate and blood pressure, leading to fainting. It is a direct response of the parasympathetic nervous system.
  • Postural Orthostatic Tachycardia Syndrome (POTS): While primarily affecting the sympathetic nervous system, POTS can also impact the parasympathetic system, leading to an abnormal increase in heart rate upon standing.

Symptoms of Parasympathetic Nervous System Disorders

  • Digestive Issues: Abnormalities in digestion such as constipation, diarrhea, or persistent nausea.
  • Urinary Problems: Difficulty in starting urination, incomplete bladder emptying, or incontinence.
  • Cardiovascular Changes: Abnormal heart rate, dizziness, and fainting spells due to blood pressure fluctuations.
  • Respiratory Difficulties: Shortness of breath or rapid breathing without exertion.

Effects of Parasympathetic Nervous System Disorders

  • Gastrointestinal Impact: Impaired digestive function can lead to malnutrition, weight loss, or severe discomfort.
  • Cardiovascular Risks: Irregular heart rhythms and blood pressure issues can increase the risk of heart attacks or strokes.
  • Quality of Life: Chronic symptoms such as fatigue, pain, and gastrointestinal distress can severely impact daily activities and mental health.


Which Activity Activates the Parasympathetic Nervous System?

Activities like deep breathing, meditation, and yoga activate the parasympathetic nervous system, promoting relaxation and digestion.

How Do You Stimulate the Parasympathetic System?

Stimulate the parasympathetic system by practicing slow, deep breathing exercises, getting adequate sleep, and engaging in mindfulness meditation.

What is Difference Between Sympathetic and Parasympathetic?

The sympathetic nervous system prepares the body for ‘fight or flight,’ while the parasympathetic system promotes ‘rest and digest’ activities.

What Happens When the Parasympathetic Nervous System is Stimulated?

Stimulation of the parasympathetic nervous system slows the heart rate, increases intestinal activity, and promotes calmness and relaxation.

AI Generator

Text prompt

Add Tone

10 Examples of Public speaking

20 Examples of Gas lighting