The concept of the life-force is central to all ancient healing traditions, like the concept of Chi in Chinese Medicine. In Ayurveda this life-force, called Prana, has five functional variations. Herbs are classified according to which of these Pranas they work on.
1. PRANA: centered in the brain, it moves downward, governing inhalation and swallowing. It relates to intelligence, power of sensory and motor functions, and primarily to the nervous and respiratory systems. 2. VYANA: centered in the heart, it acts throughout the body, governing the circulatory system and the movement of joints and muscles. 3. SAMANA: centered in the small intestine, it governs the digestive system. 4. UDANA: centered in the throat, it governs speech, energy, will, effort, memory, exhalation. 5. APANA: centered in the lower abdomen it governs all downward discharges of feces, urine, semen, menstrual fluid and the fetus. These five Pranas are commonly called the five Vayus (Vayu means air or motivating force). They are a fivefold division of the life-force and its functional differentiation in its energization of the nervous system.