Nadi, psychic nerve are the channels through which the energies of the subtle body are said to flow. They connect at special points of intensity called chakras.
Ida, Pingala and Sushumna
The Medullar Shushumna, which interpenetrates the cerebrospinal axis from the perineum to the juncture of the lamboid and sagittal suture of the cranium, the lunar Serpentine Ida of the left side, of a pale color, negative polarity; the solar Serpentine Pingala of the right side, red color, positive polarity. Those are the main nadis, but in some tantric texts more than 72,000 nadis are cited. They all start from the central channel of the chakras to the periphery where they gradually become thinner.