Autonomic nervous system (ANS)

The autonomic nervous system controls the body’s involuntary functions, such as heart rate, blood pressure, breathing, digestion and sweating.

It is divided into two main branches: the sympathetic nervous system (“fight or flight”) and the parasympathetic nervous system (“rest and digest”), with the enteric nervous system regulating the gut. The ANS constantly balances these systems to maintain homeostasis.

In pain medicine, dysfunction of the ANS is common. Overactive sympathetic activity can worsen or even maintain pain, as seen in Complex Regional Pain Syndrome (CRPS), where abnormal vasomotor and sudomotor changes accompany burning pain and hypersensitivity. Reduced parasympathetic activity, often measured as low vagal tone, is linked to chronic pain, stress and poor resilience.
The ANS interacts closely with the immune system and oxidative stress pathways. For example, the vagus nerve exerts anti-inflammatory effects through the cholinergic anti-inflammatory reflex. Therapies that restore autonomic balance — from biofeedback and vagus nerve stimulation to interventional treatments such as PRF, which can indirectly modulate