Parasympathetic Nervous System: Ways to Keep It Healthy

What Is the Parasympathetic Nervous System?

The parasympathetic nervous system (PSNS) relaxes our body and saves energy. It is a major branch of the autonomic nervous system. It regulates internal body functions, such as digestion, heart rate, and breathing.

Why Is It Called the "Rest and Digest" System?

The term "rest and digest" describes how the parasympathetic nervous system functions in a relaxed state or while eating. It reduces heart rate and blood pressure and stimulates digestion.

Role in the Autonomic Nervous System:

The autonomic nervous system is responsible for involuntary actions. The PSNS works directly against the sympathetic nervous system (SNS). While the SNS activates the "fight or flight" response in dangerous situations. The PSNS brings the body to homeostasis, conserving energy and enabling everyday functions.

Parasympathetic Nervous System at a Glance

Parasympathetic Nervous System Anatomy: Your parasympathetic nervous system anatomy depends on craniosacral outflow. It means that this system starts its functions from certain nuclei in your brain stem and from the S2 to S4 segments of the sacral spinal cord. It utilizes very long preganglionic nerve fibers that travel near the targeted organs.

1. Cranial Nerves Involved: The following are the cranial nerves that convey parasympathetic fibers from your brain stem to your head, neck, and internal organs:

• The oculomotor nerve (III) is responsible for pupil constriction and lens accommodation.

• The facial nerve (VII) innervates your lacrimal (tear), submandibular (beneath the lower jawbone), and sublingual (under the tongue and floor of your mouth) salivary glands.

• The glossopharyngeal nerve (IX) stimulates your parotid salivary gland.

• The vagus nerve (X) is the main nerve of the PSNS.

2. Sacral Spinal Nerves: The bottom end of the parasympathetic nervous system emerges from your S2-S4 segments of the spinal cord. Spinal nerves arise from the lower segments of the spine and innervate the pelvic splanchnic nerves. Such nerves regulate the organs found in the pelvic region and lower abdomen.

3. The Vagus Nerve and Its Importance: The vagus nerve comprises the biggest section of the parasympathetic nervous system, with about 75 percent of all its nerves. It functions as an important pathway for brain communication with various organs.

4. Preganglionic and Postganglionic Neurons: Parasympathetic impulses are carried via a two-neuron pathway between your central nervous system and the effector organs.

• Preganglionic Neurons: These nerves are long. They originate from the brainstem or the lower part of your spine and run a long way to reach the target organ.

• Postganglionic Neurons: These nerves are short. They originate from a nerve junction near or within the target organ.

How Does the Parasympathetic Nervous System Work?

1. Acetylcholine as the Primary Neurotransmitter: The whole process of communication in the PSNS depends mainly on a single chemical message carrier, acetylcholine (ACh). This acts as a mediator for two separate processes of transmission:

• At the Ganglion: The first nerve produces a chemical known as ACh. ACh binds to nicotinic receptors on the second nerve, generating an electrical signal.

• At the Target Organ: The stimulated postganglionic neuron covers a short distance to release ACh to the target organs.

2. Muscarinic Receptors: ACh binds to the muscarinic receptors, which are G protein-coupled receptors that start changes within the cell. There are five types of receptors, designated M1-M5. Each receptor produces a specific effect, depending on the organ it targets.

3. Communication With Target Organs: Through the activation of ACh, the parasympathetic nervous system coordinates with the target organs to reduce metabolic stress.

• Cardiovascular System: Decreases your heart rate and lessens the work of the myocardium.

• Digestive System: Increases your smooth muscle tone. It causes peristalsis and secretion of gastric acid and digestive enzymes.

• Respiratory System: It causes bronchoconstriction. It produces more mucus, reducing the size of the airways at rest.

• Ocular System: Produces miosis and ciliary muscle contraction for near vision.

• Exocrine Glands: Initiate salivation, lacrimation, and secretion of digestive juices.

Functions of the Parasympathetic Nervous System

The parasympathetic nervous system functions are as follows:

• Heart: It slows down your heart rate and the force with which your heart pumps blood.

• Lungs: It contracts the airway muscles. This results in decreased lung activity at rest.

• Eyes: Your pupils become contracted. This prevents too much light from entering the eyes. It improves nearsighted vision while causing tears to be produced.

• Digestive System: It increases the speed of digestion and redirects your body’s energy to support it.

• Pancreas: Stimulates both the exocrine and endocrine functions of the pancreas.

• Urinary System: Contraction of the detrusor muscle (of the bladder wall). Relaxation of the internal urethral sphincter to encourage urination.

• Reproductive System: Regulates certain sexual functions, including arousal (erection in males and secretion of lubricating fluids in females).

• Salivary Glands: Secretion of water, potassium ions, and salivary amylase. It is necessary for the breakdown of food in the first stage of digestion.

Parasympathetic vs Sympathetic Nervous System

Key Differences:

• Sources: The sympathetic nervous system is derived from your thoracolumbar region. The parasympathetic nervous system is derived from the craniosacral region of the spinal cord.

• Ganglionic Location: Ganglia of the sympathetic system are close to the spinal cord. It creates fast and wide-ranging effects. Ganglia of the parasympathetic system are located closer to, or even within, the target organ. Thus, it can produce more localized effects.

• Response Timing: The sympathetic system creates fast responses. The parasympathetic system reacts more slowly. This creates relaxation and recovery effects.

• Neurotransmitters: Norepinephrine is used in the sympathetic nervous system. Acetylcholine is used in the parasympathetic nervous system.

Fight or Flight vs. Rest and Digest:

• “Fight or Flight” (Sympathetic): This response occurs in the presence of stress and threats in the environment and prepares the body to act. The body's fight-or-flight mechanism increases your heart rate, directs blood to large muscles, and breaks down glucose. This avoids all unnecessary activities in the body.

• Rest and Digest” (Parasympathetic): This kicks in when the body feels at peace.

A patient asked how I can overcome the fight-or-flight response. Our doctor has advised us to drink enough water, do exercise and meditation, avoid junk food, and get 7 to 8 hours of sleep.

Organ-by-Organ Comparison:

Organs Controlled by the Parasympathetic Nervous System: The organs controlled by the parasympathetic nervous system are as follows:

• Brain.

• Heart.

• Lungs.

• Liver.

• Stomach.

• Intestines.

• Bladder.

• Sexual organs.

Common Disorders Affecting the Parasympathetic Nervous System

The associated parasympathetic nervous system disorders are as follows:

• Autonomic neuropathy (damage to the autonomic nerves).

• Diabetes-related nerve damage.

• Parkinson's disease (a neurological disorder that affects movement).

• Multiple system atrophy (a rare neurodegenerative disorder).

• Vagus nerve dysfunction.

Disorders Affecting the Parasympathetic Nervous System

Symptoms of Parasympathetic Nervous System Dysfunction:

The parasympathetic nervous system symptoms are as follows:

• Rapid heart rate.

• Digestive problems.

• Constipation.

• Difficulty urinating,

• Erectile dysfunction (unable to achieve or maintain an erection).

• Dry mouth.

• Reduced tear production.

How Doctors Diagnose Parasympathetic Nervous System Disorders

The diagnosis of PSNS disorders is as follows:

1. Past Medical History: Your doctor evaluates your symptoms, medications, past medical history, and life habits. It is one of the most crucial parts in diagnosing problems with involuntary body functions.

2. Neurological Examination: Your doctor examines your coordination, reflexes, muscle strength, and sensation to look for signs of nerve damage.

3. ECG (Electrocardiography): A test that records the heart's electrical activity. This determines if there are any disorders in your heart rhythm.

4. Tilt Table Test: The procedure measures how your heart rate and blood pressure respond to changes in your body position.

5. Heart Rate Variability (HRV): The test measures the intervals between heartbeats, typically during deep breathing. This diagnoses the condition of the vagus nerve and the work of the autonomic nervous system.

6. Autonomic Function Tests (AFT): These are standardized tests, such as the Valsalva maneuver. This measures the responses in heart rate and blood pressure.

7. MRI (Magnetic Resonance Imaging) and Blood Tests: The MRI helps to exclude any structural abnormalities. Blood tests can diagnose autoimmune or systemic disorders that affect your autonomic nervous system.

Treatment for Parasympathetic Nervous System Disorders:

The treatments for PSNS are as follows:

1. Treating the underlying condition.

2. Medications: Your doctor will advise on medications based on your symptoms. For instance, Metoclopramide can be used for gastroparesis (delayed gastric emptying), and Midodrine or Droxidopa can be used for orthostatic hypotension (low blood pressure when standing). Other drugs can help with bladder and bowel movements.

3. Physical Therapy: It helps strengthen your muscles and improve your balance and mobility if there is nerve damage.

4. Lifestyle Changes: Drinking enough fluids, maintaining a healthy diet, using compression stockings and other supportive clothing, getting adequate sleep, and managing stress can help manage your symptoms.

5. Vagus Nerve Stimulation (Where Applicable): The vagus nerve contains 75% of parasympathetic fibers. Vagus nerve stimulation is considered to help maintain the balance of the nervous system. Depending on the condition, it can be done by:

• Implantable devices.

• Transcutaneous devices (noninvasive devices that use electric current to target tissue).

How to Improve Parasympathetic Nervous System Function Naturally

The ways to improve PSNS function naturally are as follows:

• Deep breathing.

• Meditation.

• Yoga.

• Regular exercise.

• Healthy sleep.

• Balanced nutrition.

• Stress management.

• Staying hydrated.

When to Consult a Doctor?

Consult your doctor if you have problems with

• Digestion.

• Dizziness while standing up.

• Heart rate irregularities.

• Problems with your urinary bladder or sexual function.

Conclusion:

The parasympathetic nervous system (PSNS) is the body’s critical “rest and digest” system. It slows the heart rate, preserves energy, and aids digestion. It is important for your health and emotions. It acts as an effective counterbalance to the high-energy requirements of the sympathetic nervous system. About 75% of the parasympathetic fibers travel in the vagus nerve. It is imperative to support the PSNS system to maintain proper well-being and manage stress. Seek help from a nerve specialist if you are always fatigued or unable to relax.

Key Takeaways:

• The parasympathetic nervous system (PSNS) regulates your body's functions of relaxation and repair.

• It slows the heart rate and regulates digestion and excretion of wastes.

• Problems occurring with the parasympathetic nervous system can interfere with body processes. This leads to digestive issues, urinary retention, changes in blood pressure, and other similar symptoms.

• The parasympathetic nervous system reduces stress levels, helps balance the fight-or-flight response, and regulates bodily functions.

• PSNS uses acetylcholine as the main neurotransmitter. Both the preganglionic and postganglionic nerves use acetylcholine to communicate with organs.