Hi to all. Some of the information in this thread is not quite clear. Let's revisit all of it:
FIRE PATH
The Fire Path starts at the mouth, and goes down the front of the torso in the center to the point between your legs, Hui Yin, the perenium. This point is located between your genitals and anus. This first segment of the Fire Path is called the Conception Vessel. It then travels from the perenium, up the center of the back, outside the back of the spine, up the neck and back of the head, to the top of the head, the Bai Hui, and down the front of the head to the mouth. This segment is called the Governing Vessel.
The tongue should touch the roof of the mouth, right behind the teeth, to bridge the two segments, or Vessels.
This is also called the small circulation or the microcosmic orbit. Same thing.
Qi (energy) flows in the Fire Path all day, every day, in a 24 hour cycle*. In qigong, we are only following this natural path and enhancing it slowly. keyword: slowly. too much too soon is what makes it dangerous. *Of course, every one of the trillions of cells in your body is permeated with Qi, but it is more abundant in the Vessels, meridians, channels, and acupoints. More on this later.
WIND PATH
The Wind Path is exactly the same as the Fire path, except the flow is in the opposite direction. it is used to cool down the body, mainly in the front of the body. This is done as part of Kan and Li, water and fire, training. It is a vital part of your Embryonic Breathing practice, in which you lead Qi up from the real lower dan tian (elixir field), and down from the diaphragm, or middle dan tian, and they meet in the center, the huang ting (yellow yard).
WATER PATH
The Water Path is from the lower energy center - the real lower dan tian, up THROUGH the spine to the upper energy center, or upper dan tian, in the center of the brain. The Water Path is dangerous and should not be used without the guidance of a qigong instructor. Dangers are brain damage, disturbed sleep/hormone production, mania, insanity, otherwise known as the popular 'Qi psychosis' everyone likes to talk about. The general rule is, don't try to work with the Water Path until you've mastered both Embryonic Breathing and Small Circulation. Also, you must have prepared the mind itself psychologically and emotionally, and developed a strong ability to hold the upper energy center. So, don't. - unless you are truly practicing a great deal, studying Buddhist or Taoist philosophies for preparing the mind, and working toward true enlightenment.
The word enlightenment is thrown around casually, especially in America, but it is exceedingly difficult to attain, and should not be confused with a general state of raised awareness, or some intermediate level of insight. The practice is very involved and serious, not casual (and I would guess that only a very few laypersons worldwide will achieve true enlightenment within any given 100 year period, especially nowadays).
Qi is supplied from the vessels to the rest of the body.
TERMINOLOGY
As for the terminology between different systems, chakras, energy centers, Qi, prana, etc; there are similarities and differences between them all. But we have to realize this: the body is the body, and the terms we use to define it do not change the truth of its real structure. So, we should be looking to find a 'unified theory' for viewing the physical/energetic body which analyzes the intuition, experience, and wisdom of the various disciplines, with a logical, scientific perspective based in reality. Whatever words and concepts you choose to use to try and define it, the human body is a living electromagnetic field. The energy we are discussing is not a metaphor, or some vague, mystical, new age energy that isn't based in reality. It is bioelectricity.
Ultimately, once we develop a strong feeling, or in other words develop a strong sensation of your Qi circulation in our Qigong practice, it is best to empty the mind of all words, concepts, and attachments, and simply experience it openly
QI CIRCULATORY SYSTEM
Someone mentioned: "Obviously there is no physical channel..." This is not true. We cannot see the acupoints or channels with the physical eye, but they are there, just as we cannot see gravity with the eye, but know that it exists. Because they exist, they are made of matter. All matter can be 'seen' eventually, by some means. We just do not yet have the scientific instrument we require. (However, the acupuncture cavities have been measured and they are more electrically conductive areas on the body.) The Vessels on the other hand we CAN see: the tendons. You might argue with your acupuncturist about this, but if they study the topic carefully, with a logical, scientific mind, it is very plain to see.
So, the governing vessel is the stripe of tendons that goes up your back, outside the spine, and the conception vessel is the stripe of tendons that goes down the front of the body.
If you doubt it, look at the more specific areas, like the exact shape of the Conception Vessel, and of the Belt Vessel: they match the tendons.
Different tissues in the body have different bioelectrical properties, different electric conductivity, and so Qi circulates and accumulates within each differently.
HEADACHES
Often its just too much Qi in the head. Simple as that. Physically, you can lead it out by tapping the head, if the headache isn't that bad. And, mentally, put your mind in the lower energy center, real lower dan tian, or circulate in the fire path, or whatever you feel you need to do to lead qi away from the head.
What yeniseri said is so true - your own experience of different levels of health and various illnesses is the best teacher.
Great discussion everyone, thank you all.
PRACTICE
Practice, practice, practice.
And enjoy your practice!
David Silver
YMAA Assistant Qigong instructor