Originating in the brainstem, the autonomic nervous system:

• Controls our main organs: eyes, heart, lungs, kidneys, bowels, etc.
• Regulates our internal conditions in order to maintain the homeostasis (self-regulation system of our vital body functions) and physiological stability.

The autonomic nervous system is made of two main divisions:

• Sympathetic nervous system associated to the state of action: its role is to prepare the body, put it in a state of alertness and prepare it for an activity.
  Example: to prepare the subject to the intense muscular activity required by the protection and defense in response to the stimulations of our environment, pupils dilate, the heart rate increases, blood vessels contract and the blood pressure increases.
• The parasympathetic nervous system associated to the resting state: its role is to slow down the body’s functions and thus conserve energy.
  Example: to protect the retina from excessive lighting, the pupil retracts; the heart rate slows down to give the heart muscle long periods of rest and recovery.

These two divisions act in an antagonist manner like a dynamic balance. The easiness with which we can switch from a state of excitement to a state of calm is related to the capacity of our autonomic nervous system to regulate our internal physiological response..

The adaptability of our autonomic nervous system faced with external (environment…) and internal (emotions, stress..) solicitations enables the body to maintain a proper homeostasis. Conversely, a lack of flexibility exposes the body to different somatic and physiological pathologies.

Several recent clinical studies reported that a rigid autonomic nervous system could be explained by a lower parasympathetic nervous system tone (also called vagal tone).