Two parts make up our nervous system, the central nervous system and the autonomic or vegetative nervous system.

The autonomic nervous system, which regulates all bodily processes that occur automatically, is subdivided into two systems with opposing actions: the parasympathetic nervous system and the sympathetic nervous system. They control the impacts of stress and relaxation on our body. 

The parasympathetic nervous system is responsible for the involuntary functions of the body, intended to temper the unconscious neurological functions of the body.

The action of the parasympathetic nervous system opposes that of the sympathetic system by taking care of slowing down the functions of the organism in order to save energy.

The parasympathetic system acts mainly on digestion, growth, the immune response, energy reserves.

Heart

• Slowing of heart and respiratory rate and the force of contraction of the atria;
• Decrease in blood pressure by vasodilation.

lungs

• Bronchial contraction and secretion of mucus.

Digestive tract

• Increased motor skills;
• Relaxation des sphincters ;
• Stimulation of digestive secretions.

Bladder

• Contraction.

Pupil

• Myosis (contraction pupillaire).

Genitals

• Erection.

glands

• Secretion from the salivary and sweat glands;
• Exocrine pancreas: stimulation of secretion;
• Endocrine pancreas: stimulation of insulin secretion and inhibition of glucagon secretion.

The pneumogastric nerve is a cranial nerve that descends through the thorax and joins the abdomen. This nerve works thanks to a neurotransmitter called acetylcholine, which acts at all the nerve endings involved. It is this substance that causes the parasympathetic effects.

The sympathetic system and the parasympathetic system can control many organs, as well as:

• blood pressure ;
• heart rate ;
• body temperature;
• weight, digestion;
• the metabolism ;
• water and electrolyte balance;
• sweating;
• urination;
• defecation;
• sexual response and other processes.

We must be vigilant because the functions can be reciprocal: the influx of the sympathetic system increases the heart rate; the parasympathetic diminishes it.

Disorders of the autonomic nervous system cause abnormalities or vegetative failure that alter the autonomic nerves or parts of the brain and which can therefore affect any system in the body.

Most of the time, these two systems are stable and depending on the needs, their activity is constantly adjusted. These two systems are silent: they operate without our knowledge in complete autonomy. When the environment changes suddenly or an unforeseen event occurs, one or the other becomes predominant depending on the circumstances and the induced reactions may be visible.

Common causes of autonomic disorders are:

• Diabetes (the most common cause);
• Diseases of the peripheral nerves;
• Aging;
• Parkinson disease.

Vegetative disorders are frequently treated on the basis of the cause, if the cause is not present or cannot be treated, treatment will focus on relieving the symptoms.

• Reduced or no sweating: avoiding hot environments is useful, if sweating is reduced or absent;
• Urinary retention: if a bladder cannot contract normally, a catheter may be offered;
• Constipation: A high fiber diet is recommended. If constipation persists, enemas may be necessary.

Clinical examinations

• Check for signs of autonomic disturbances, such as postural hypotension (blood pressure and heart rate measurement, electrocardiography: to determine if changes in heart rate are normal during deep breathing and the Valsalva maneuver;
•  examine the pupils for abnormal responses or a lack of response to changes in light;
•  eye examination: a dilated, non-reactive pupil suggests a parasympathetic lesion;
•  Genitourinary and rectal reflexes: Abnormal genitourinary and rectal reflexes may indicate abnormalities in the autonomic nervous system.

Additional tests

• Sweat test: The sweat glands are stimulated by electrodes that are filled with acetylcholine and placed on the legs and forearms. The amount of sweat is then measured to determine if the sweat production is normal;
• Tilting table test: observe the variations in blood pressure and heart rate during a change of position;
• Determine how the blood pressure varies during the Valsalva maneuver (try to force an exhale without allowing air to pass through the nose or mouth, similar to exerting during a bowel movement).