This is a great question that can be answered in many ways. The best way is to experience it. If you must get out of your body and into your thinking self, consider the following:
Gasotransmitters– Nitric Oxide and Hydrogen Sulfide, and their effect on microbiota.
Quantum Mechanics and Electro-conductivity, describing nature at the smallest scales of energy levels of atoms and subatomic particles. Electricity can modulate the production and release of all-natural super powerful neuropeptides and neurotransmitters.
The ancient concepts of Qi and Meridians, that modern researches are attempting to explain and rediscover, possibly in the form of the Interstitium.
Qi Running in the Meridians as Interstitial Fluid
Poetic Theories of ancient times
can explain it all,
to really understand acupuncture,
you must experience it 🙂