Medical News Today: What is the autonomic nervous system?

The autonomic nervous system is a complex network of cells that controls the body’s internal state. It regulates and supports many different internal processes, often outside of a person’s conscious awareness.

This article will explain the autonomic nervous system, or ANS, how it works, and the disorders that can affect its functioning.

a man exercising and checking his heart rate which is regulated by the Autonomic nervous systemShare on PinterestThe ANS helps to regulate many of the body’s internal functions, such as heart rate.

The nervous system is a collection of cells that send and receive electrical and chemical signals throughout the body.

The nervous system consists of two main parts:

  • The central nervous system: This consists of the brain and spinal cord.
  • The peripheral nervous system: This contains all the neurons outside of the central nervous system.

The ANS is part of the peripheral nervous system. It is a collection of neurons that influence the activity of many different organs, including the stomach, heart, and lungs.

Within the ANS, there are two subsystems that have mostly opposing effects:

  • The sympathetic nervous system (SNS): Neurons within the SNS generally prepare the body to react to something in its environment. For example, the SNS may increase heart rate to prepare a person to escape from danger.
  • The parasympathetic nervous system (PNS): Parasympathetic neurons mostly regulate bodily functions when a person is at rest.

The nervous system regulates the internal environment of the body. It is essential for maintaining homeostasis.

Homeostasis refers to the relatively stable and balanced conditions inside the body that are necessary to support life. Some of those that homeostasis regulates include:

The ANS receives information from the environment and other parts of the body and regulates the activity of the organs, accordingly.

The ANS is also involved in the following bodily functions:

  • producing bodily fluids, such as sweat
  • urination
  • sexual responses

One critical function of the ANS is to prepare the body for action through the “fight or flight” response.

If the body perceives a threat in the environment, the sympathetic neurons of the ANS react by:

  • increasing heart rate
  • widening the airways to make breathing easier
  • releasing stored energy
  • increasing strength in the muscles
  • slowing digestion and other bodily processes that are less important for taking action

These changes prepare the body to respond appropriately to a threat in the environment.

The fight or flight response of the ANS evolved to protect the body from dangers around it. However, many stressful aspects of daily life can also trigger this response.

Examples include:

  • work-related stress
  • financial concerns
  • relationship problems

Chronic stress can cause the ANS to trigger the fight or flight response over long periods. This continuation will eventually harm the body.

Some drugs can also affect the way the ANS functions. Examples include:

Autonomic disorders affect the functioning of the ANS. They can sometimes occur as a result of the following:

  • aging
  • damage to neurons within the ANS
  • damage to specific parts of the brain

Certain medical conditions can also affect the ANS. Some common causes of autonomic disorders include:

Less common causes of autonomic disorders include:

  • multiple system atrophy (MSA)
  • spinal cord disorders
  • Lambert-Eaton syndrome
  • botulism
  • viral infections
  • damage to nerves in the neck

Autonomic disorders can be serious. People who experience symptoms of an autonomic disorder should see a doctor for a full diagnosis.

Talking to a doctor is particularly important for people with diabetes or other conditions that can increase the likelihood of autonomic disorders.

To diagnose the cause of ANS symptoms, a doctor will first assess a person’s medical history for risk factors.

A doctor may also request one or more of the following:

  • Tests to detect orthostatic hypotension: A doctor may measure OH using a tilt-table test. In this test, a person lies on a bed that tilts their body at different angles while a machine records their heart rate and blood pressure.
  • Electrocardiogram: This test measures electrical activity within the heart.
  • Sweat test: This test assesses whether the sweat glands are functioning correctly. A doctor uses electrodes to stimulate the sweat glands and measures the volume of sweat they produce in response to the stimulus.
  • Pupillary light reflex test: This test measures how sensitive the pupils are to changes in light.

The ANS regulates the internal organs to maintain homeostasis or to prepare the body for action. The sympathetic branch of the ANS is responsible for stimulating the fight or flight response. The parasympathetic branch has the opposite effect and helps regulate the body at rest.

Autonomic disorders have many different causes. They can occur as a natural consequence of aging or as a result of damage to parts of the brain or ANS. They may also occur as a result of an underlying disorder, such as diabetes or Parkinson’s disease.

A person should see a doctor if they experience symptoms of a possible autonomic disorder. A doctor will work to diagnose the cause of the symptoms and prescribe appropriate treatments.

Medical News Today: What to know about vasovagal syncope

The term vasovagal syncope describes fainting that occurs in response to a sudden drop in heart rate or blood pressure. The resulting lack of blood and oxygen to the brain is what causes a person to pass out.

Doctors sometimes refer to vasovagal syncope (VVS) as neurocardiogenic syncope or reflex syncope. This condition typically occurs when the body overreacts to a stimulus that induces a state of fear or emotional distress.

Other causes may include severe pain, exhaustion, or sudden changes in body posture. Some people have a predisposition to these episodes due to a health condition that affects blood pressure or the heart.

Although a person may sometimes sustain injuries as a result of passing out, VVS is generally harmless. However, a medical diagnosis is necessary to rule out more serious medical conditions.

In this article, we outline some common symptoms and causes of vasovagal syncope. We also cover the treatment options available and provide tips on how to prevent fainting episodes.

a man looking faint as he is experiencing Vasovagal syncopeShare on PinterestLightheadedness, dizziness, and weakness can be signs that a person will faint.

Some people who experience VVS do not notice any warning signs before fainting. Others may have symptoms such as:

People who experience these symptoms before fainting should lie down somewhere safe. Lying down will help the body maintain adequate blood flow to the brain, which may prevent fainting. It will also minimize the risk of a fall or injury in the event of fainting.

A person who has fainted may feel tired, lightheaded, or nauseated when they come round.

VVS occurs when the nerves that regulate heart rate and blood vessel constriction temporarily lose some of their normal regulation.

Malfunctions generally occur when a stimulus, such as fear, or an abrupt change in body posture causes the blood vessels to widen suddenly. This widening leads to a sudden drop in blood pressure and a resulting lack of blood and oxygen to the brain. This lack of oxygen is what causes fainting.

People may experience VVS for different reasons. Some common triggers include:

  • fear
  • the sight of blood or gore
  • getting blood drawn
  • standing for a long time
  • sudden changes in posture
  • straining, such as during bowel movementssevere pain
  • intense exercise
  • exposure to heat

A person who has experienced VVS may feel tired, weak, and nauseated when they come round. It is important that they rest before getting up and continuing with their day.

In some cases, people may need to seek emergency medical attention after a fainting episode. Generally, medical care is only necessary for people who experience the following scenarios and symptoms:

  • fainting while pregnant
  • falling from a significant height
  • sustaining a head injury or other severe injury
  • loss of consciousness
  • chest pain or difficulty breathing
  • confusion, slurred speech, or issues with vision or hearing
  • involuntary movements of the body

People who have previously experienced VVS should talk to their doctor if they experience any new triggers or symptoms.

People should also see a doctor if they experience fainting for the first time. However, it is not always possible to diagnose VVS from a single episode of fainting.

Some types of syncope can occur as a result of an underlying medical condition that requires treatment. Examples of such conditions include:

Typically, doctors will begin a diagnosis of VVS with a review of the person’s medical history and any other symptoms. They will also conduct a physical examination. As part of this examination, the doctor will take blood pressure readings while the person is standing, sitting, and lying down.

A doctor may also attempt to rule out alternative causes of fainting using one or more tests. Examples of such tests include:

  • Electrocardiogram (EKG), which measures electrical activity in the heart.
  • Echocardiogram, which assesses heart motion and blood flow through the heart.
  • Exercise stress test to evaluate heart function in response to exercise.
  • Tilt-table test, in which the doctor will secure a person to a padded table that tilts at different angles. Various monitors detect and record heart activity, blood pressure, and oxygen levels while the table positions the person at different angles.

VVS does not typically require treatment. However, a person may sometimes be slow to regain consciousness after an episode of fainting. A bystander can intervene by laying the person on their back and raising their legs in the air. Doing this may help restore blood flow to the brain, thereby helping the person regain consciousness.

According to a 2016 review, there are limited treatment options for people with VVS. Doctors advise people with this condition to avoid known fainting triggers and take precautions to prevent injury when signs of imminent fainting begin.

Medications are not usually necessary for VVS. However, in some circumstances, the following medications may be effective in reducing the frequency of VVS episodes:

  • Alpha-1 adrenergic agonists: These drugs help raise blood pressure.
  • Fludrocortisone: A type of corticosteroid that can help maintain blood pressure by increasing sodium and fluid levels in the body.
  • Selective serotonin reuptake inhibitors (SSRIs): Antidepressant medications that may help moderate the nervous system response.

However, further studies are necessary to determine the effectiveness of these and other medical treatments for VVS.

VVS is not always completely preventable. However, a person may be able to reduce the number of fainting episodes that they experience.

A person’s doctor may provide the following recommendations for preventing VVS and the associated complications:

  • identifying and avoiding situations that trigger fainting episodes
  • engaging in moderate exercise
  • drinking plenty of fluids to maintain blood volume
  • consuming a diet that is higher in salt
  • wearing compression stockings
  • discontinuing medications that lower blood pressure
  • immediately sitting or lying down when feeling faint

As with prescription medications, these preventive lifestyle approaches may work for some people and not others. Various factors, such as the person’s blood pressure and heart function, may determine the effectiveness of these approaches.

Vasovagal syncope refers to fainting that occurs in response to a sudden drop in heart rate or blood pressure.

Vasovagal syncope is usually not dangerous. However, people should seek medical attention if they faint when pregnant, experience additional symptoms, or fall and injure themselves when fainting. People should also see a doctor if they are unsure of the cause of fainting.

There are no standard treatments for vasovagal syncope. Instead, treatment generally involves making certain dietary and lifestyle changes, as well as avoiding potential triggers of fainting.