Nadi word (Naa + Dee) comes from the root Nadya which mean flow. The word Nadi literally means a flow of energy. If someone can fine tune their perception, these Nadis will appear to be thousands of fine, wire like structures conducting the energy. They are shiny and sparkling, just exactly in the shape and size of our physical bodies.
According to Shiva Samhita, a major text on Hatha Yoga, there are altogether 350,000 nadis in our energy body. In other text like Gorakh samhita this number stands out to be 72,000. There are thousands upon thousands of nadis within this superstructure of the gross body and they distribute consciousness and prana to every atom.
Among these thousands of Nadis, there are 15 principle channels which are the main supply pathways. They further keep sub-dividing into thousands of minor channels. Tantra was the first discipline to explain in details the existence of these Nadis along with Chakras in the human body. They are however, experiential concepts which cannot be brought under the scope of objective analysis. As they are non physical entities its difficult to perceive them with sensory apparatus.
3 nadis are accepted all across the Yogic system as the major passages of pranic currents. These are named as:
IDA: The left channel, also called the Chandra or the Lunar passage. This is a passive polarity which governs the metal aspect of human personality. Ida is associated with faculties of mind and all the functions that happens in this realm. It is said to govern the emotions, creativity, thinking, intellect, feelings, sensations and expression of desires and wishes. Ida is feminine in nature. Originating from mooladhara chakra it ends up in the left part of the brain. Physically it is linked with the left nostril. When the left nostril dominates it’s the Ida through which the prana is flowing.
PINGALA: The right channel, also called the Surya or Solar passage. This nadi is the active polarity which governs the physical aspect of human personality. Pingala is associated with physical functions of the body, action, dynamism, determination, strength and vigour. It governs the functions of physical body and makes a person extrovert. Pingala is masculine in nature. Originating from mooladhara chakra it ends up in the right side of the brain. Physically it is linked with the right nostril. When right nostril dominates, it’s the pingala that influences the personality as pana flows through the right passage.
SUSHUMNA: The middle channel, sushumna is the neutral passage. This is associated with the spiritual aspect of human personality. Its governs the spiritual actions and endevours, the self reflective abilities and the quest of search for Self. Sushumna remains inactive naturally and prana in its course flows mostly through ida and pingala, keeping the person oscilating the world of mind and body. Its only when sushumna starts flowing, one traverses through the dimension of spirit and becomes aligned to the real self.