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The autonomic nervous system

The autonomic nervous system is divided into two branches, the sympathetic nervous system (SNS) and the parasympathetic nervous system (PSNS)

The sympathetic nervous system

When one experiences stress, the sympathetic nervous system takes over and brings about a heightened state of alertness, which is characterized, in particular, by an increased heart rate..

At rest, on the contrary, the parasympathetic nervous system kicks in, lowering our state of alertness and our heart rate..

The sympathetic nervous system is associated with action: it causes the organism to go into a state of alert, and prepares it for activity.

The sympathetic nervous system innervates the cardio-accelerating center of the heart, the lungs (increased ventilatory rhythm and dilatation of the bronchi), and the nonstriated muscles (artery contraction). It releases adrenaline and noradrenaline.

The parasympathetic nervous system

The parasympathetic nervous system has two major functions: slowing bodily functions, thus preserving energy.

As opposed to the sympathetic nervous system, it innervates the cardio-moderator center of the heart, the lungs (slower ventilatory rhythm and contraction of the bronchi) and the nonstriated muscles (artery dilatation).
It uses acetylcholine (ACh) as its neurotransmitter.

Facing stress

Sympathetic and parasympathetic divisions function antagonistically, to preserve a dynamic modulation of vital functions.

How easily one can switch from a state of alertness to a state of calm depends on how swiftly the autonomic nervous system can alter heart rate.

The autonomic nervous system is highly adaptable, and allows the organism to maintain its balance when experiencing strain or stress. Conversely, a lack of flexibility and a rigid system can lead to somatic and psychological pathologies.