Autonomic nervous system (A complete guide)

Do you ever think about your own breathing, heart beat, or how your stomach digests food?

These are involuntary processes that your body carries out without you even needing to think about it.  

The autonomic nervous system is the part of the sensory system that controls the internal organs of the body, including the veins, stomach, digestive system, liver, kidneys, bladder, genitals, lungs, heart, and sweat and salivary glands. 

The autonomic nervous system has two primary divisions: 

·      Sympathetic

·      Parasympathetic 

After the autonomic nervous system gets information about your internal organs and the external environment, it reacts by activating or inhibiting different parts of your body.

If the external environment is telling your body to slow down and digest food for example, this most likely occurs through the parasympathetic division.

On the other hand, if a bear is running after you, your sympathetic nervous system will increase your heart rate, dilate your pupils, and mobilize your skeletal muscles. 

The parasympathetic nervous system is sometimes referred to as the “rest-and-digest” system, whereas the sympathetic nervous system is known as the “fight-or-flight” system. 

How does the autonomic nervous system transmit information throughout the body?

An autonomic nerve pathway includes two nerve cells, which are called neurons. One neuron is situated in the brainstem or spinal cord.

It is connected to the next neuron via nerve filaments, which are situated in a group of nerve cells (called an autonomic ganglion).

Nerve fibers from these ganglia connect to internal organs through something called a synapse.

A synapse is the space between a neuron and its target cell, whether that is another neuron or in this case, an internal organ.

The majority of the ganglia for the sympathetic division are found outside the spinal cord on its two sides.

The ganglia for the parasympathetic division are situated close or in the organs they communicate with. 

What is the function of the autonomic nervous system?

The autonomic nervous system controls many internal physiological processes throughout the body, for example:

·      Blood pressure

·      Heart and breathing rates

·      Body temperature

·      Digestion

·      Metabolism (thus affecting body weight)

·      The balance of water and electrolytes (such as sodium and calcium)

·      The production of body fluids (saliva, sweat, and tears)

·      Urination

·      Defecation

·      Sexual response

 Numerous organs are controlled by either the sympathetic or the parasympathetic division.

In some cases the two divisions act on the same organ.

For instance, the sympathetic division of the autonomic nervous system activates the circulatory system, and the parasympathetic division inhibits it.

Generally, the two divisions cooperate with each other to make sure that the body reacts appropriately to various circumstances in the internal and external environment.

Function of Sympathetic division

·      Prepares the body for dangerous or crisis circumstances—also known as the “fight-or-flight” response  

If your body perceives a threat or any dangerous situation, the sympathetic division of the autonomic nervous system increases the heart rate to make breathing easier and enhance blood flow to the skeletal muscles, which makes it easier to move around or run away.

This division also makes palms sweat, pupils dilate, and hair to stand on end (i.e., goosebumps).

The parasympathetic division of the autonomic nervous system inhibits the bodily functions that are less important in dangerous situations, such as digestion and urination. 

Function of parasympathetic division

·      Controls body processes during non-threatening circumstances

For the most part, the parasympathetic division of the autonomic nervous system reestablishes the body’s homeostasis.

It lowers the pulse and lowers blood pressure . It activates the digestive tract to promote digestion and absorption of nutrients as well as excretion of waste.

Energy from the digested food is used to restore and assemble tissues. 

How does the autonomic nervous system communicate with different parts of the body to control their function?

Two chemical messengers (neurotransmitters) are used to communicate within the autonomic nervous system:

·      Acetylcholine

·      Norepinephrine

Nerve fibers that release acetylcholine are called cholinergic filaments. Filaments that emit norepinephrine are called adrenergic fibers.

For the most part, acetylcholine has parasympathetic (inhibitory) effects and norepinephrine has  sympathetic (activating) effects.

Nonetheless, acetylcholine also has some sympathetic impacts.

For instance, it in some cases activates sweat glands or makes the hair stand on end to produce goosebumps.

What are the symptoms of disorders associated with autonomic nervous system malfunction? 

Signs and manifestations of autonomic neuropathy depend upon which nerves are affected. 

Symptoms of autonomic nervous system malfunction may include: 

Dizziness and fainting when standing, brought about by an abrupt drop in blood pressure

Urinary problems, for example, trouble initiating urination, incontinence, trouble detecting a full bladder and inability to totally empty the bladder, which can prompt urinary tract diseases. 

Sexual difficulties, including issues getting or keeping up an erection (erectile dysfunction) or discharge issues in men.

In women, issues include vaginal dryness, low sex drive and trouble achieving sexual pleasure.

Difficulty digesting food,for example, feeling full after a couple of bites of food , loss of appetite, diarrhea, constipation, stomach distension (bloating), queasiness, heaving, trouble swallowing and indigestion.

These symptoms can arise because of changes in stomach capacity.

Sweating anomalies, for example, perspiring excessively or t00 little, which influences the body’s ability to regulate internal temperature. 

Inability to recognize, low blood sugar (hypoglycemia), because the warning signals, such as getting shaky, aren’t there.

Sweating abnormalities,such as sweating too much or too little, which affect the body’s ability to regulate internal temperature.

Sluggish pupil reaction,making it difficult to adjust from light to dark and seeing well when driving at night.

Exercise intolerance,which can occur if your heart rate stays the same instead of adjusting to your activity level.

What are the causes of autonomic nervous system disorders?

Many different diseases can cause autonomic nervous system dysfunction, which is also known as autonomic neuropathy.

Autonomic neuropathy can also be a side effect from medication used for the treatment of other conditions.

Some common reasons for autonomic neuropathy include: 

·      Irregular protein development in organs (amyloidosis), which influences the organs and the sensory system. 

·      Immune system diseases, in which your body’s own immune system or defense mechanism attacks and harms portions of your body, including your nerves.

Some examples include Sjogren’s disorder, fundamental lupus erythematosus, rheumatoid joint pain and celiac disease.

Guillain-Barre syndrome is an autoimmune disease that happens quickly and can influence autonomic nerves. 

·      Certain malignant growths (paraneoplastic disorder) can also cause autonomic neuropathy. 

·      Diabetes, particularly poor glucose control, is the most well-known reason for autonomic neuropathy. It can slowly cause nerve damage all throughout the body. 

·      Certain medications, including a few therapies that are used to treat malignant growths (i.e., chemotherapy). 

·      Certain immune disorders. Some infections and microscopic organisms, for example, botulism, Lyme disease and HIV, can cause autonomic neuropathy.

What are the risk factors for autonomic neuropathy? 

Factors that may increase your risk of developing autonomic neuropathy include: 

·      Diabetes. Diabetes, particularly when ineffectively treated, increases your risk of autonomic neuropathy and other nerve damage.

You are at the most serious risk if you have issues controlling your blood glucose levels. 

·      Different sicknesses. Amyloidosis, porphyria, hypothyroidism and malignancy (normally because of reactions from treatment) additionally can increase the risk of developing autonomic neuropathy.

How is autonomic neuropathy usually diagnosed? 

Your primary care physician will get some information about your symptoms and perform a thorough physical examination.

He or she also may prescribe blood tests to check for: 

·      Diabetes

·      Sjogren’s disorder and other immune system diseases

·      Certain conditions such as HIV or Lyme disease

Physical examination tests you may have include:

·      Tilt-table test. In the tilt-table test, you lie on a table, and it will tilt to raise your body as though you were standing.

Your primary care physician will monitor your pulse and other body functions as your position changes. 

·      Quantitative sudomotor axon reflex test. This uses minimal electrical current to test how your perspiration organs are functioning. 

·      Urodynamic tests. These tests check how well your bladder stores and discharges urine. 

·      Ultrasound. This uses high-recurrence sound waves to get pictures of your bladder or other organs so your primary care physician see what is going on inside your body. 

What is the treatment for autonomic neuropathy? 

Your doctor will probably first treat the disease that originally caused your nerve damage.

For example, if you have diabetes, you will need to control your blood sugar with diet, exercise, and possibly medicine.

For autoimmune diseases, like Sjogren’s syndrome, you will get medicine to control your immune system and reduce the inflammation in your body.

Your doctor also might recommend other things to ease specific symptoms.

·      To treat digestive symptoms:

·      Change your diet. Eat smaller meals so you do not feel too full. Add fluid and fiber to your diet to prevent bloating and constipation.

·      Laxatives can help with constipation, and other medicines can treat diarrhea and stomach pain.

·      Sleep with the head of your bed raised to prevent heartburn.

·      To treat urinary symptoms:

·      Drink fluids and empty your bladder at set times during the day. This can help your bladder hold more fluid.

·      Oxybutynin (Ditropan XL) and tolterodine (Detrol) stop your bladder muscle from squeezing too often. Bethanechol helps you empty your bladder all the way.

·      Use a catheter. This tube goes into your bladder to help empty it.

·      To treat sweating problems:

·      A few drugs can help decrease your sweating, including glycopyrrolate (Robinul, Robinul Forte) and botulinum toxin.

·      If you do not sweat enough, stay inside when it is hot outdoors.

·      To treat heart and blood pressure symptoms:

·      Take a medication that raises your blood pressure, such as fludrocortisone or midodrine and pyridostigmine (Mestinon).

·      Take medicine to control your heart rate. Beta-blockers can help bring your heart back into a normal rhythm.

·      Stand up slowly so you do not get dizzy upon standing.

·      Get extra salt and fluid in your diet to help raise your blood pressure. Only do this if your doctor recommends it. In some cases, it can raise your blood pressure too high or cause swelling.

·      To treat sexual symptoms:

·      Drugs like sildenafil (Revatio, Vi**ra), tadalafil (Cialis), and vardenafil (Levitra, Staxyn) can help men get — and keep — an erection.

·      Women can try a water-based lubricant to make sex more comfortable.

In this article, we discussed the function of the autonomic nervous system and causes and treatment of autonomic nervous system dysfunction. 

Frequently asked questions (FAQs) about the autonomic nervous system:

What are the three parts of the autonomic nervous system? 

The autonomic nervous system includes the sympathetic nervous system, parasympathetic nervous system, and the enteric nervous system.

Some resources do not include the enteric nervous system as part of the autonomic nervous system. 

What is the autonomic nervous system and what does it control? 

The autonomic nervous system regulates the function of our internal organs such as the stomach, heart, and intestines.

What diseases affect the autonomic nervous system?

Autonomic nervous system disorders can occur alone or as a result of another disease such as Parkinson’s disease, diabetes, cancer, autoimmune disease, or alcohol abuse. 

Primer on the Autonomic Nervous System 

This book goes into detail on how the autonomic nervous system functions to regulate our internal organs, particularly in response to stressful situations. 

The Integrative Action of the Autonomic Nervous System 

This book is a great resource for information about the autonomic nervous system and how critical it is for the body to function at optimal levels. 


Overview of the Autonomic Nervous System. Merck Manuals. December 2018. 

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