Some science behind the scenes
Meridians, arteries and veins
Very very roughly speaking there is also a correspondence between the ‘hot’ yang energy and the sympathetic nervous system [red below]or the Arteries and the ‘cold’ yin energy [blue below]and the parasympathetic nervous system or veins.
One might think of the nerves and blood vessels as the communication system in a computer network, whereas the energy flows are the software messages that travel over the network. The difference is important as a ‘message’ has information content and can be directed to specific points on the body. A nervous impulse, neurotransmitter or hormone has no information content – it is just a carrier.