The nadis are nerve channels or tubes in the astral body through which prana flows. Asanas and Pranayama are designed to purify nadis, for when they are blocked prana cannot flow freely and poor health results.
According to the ancient yogis, there are about seventy-two thousands (72, 0000) nadis. Of all the nadis, the most important is the Sushumna, whose counterpart in the physical body is spinal cord. On either side of sushumna, are two other nadis called Ida and Pingala, which corresponds to the sympathetic ganglia of the spinal cord.
Kundalini is a dormant or static cosmic energy, often depicted as a coiled snake. It is located at the base of the Sushumna in the Muladhara chakra and aroused or activated by Pranayama and other yogic practices.