Nādi (the Sanskrit for "tube, pipe") are the channels through which, in traditional Indian medicine and spiritual science, the energies of the subtle body are said to flow. They connect at special points of intensity called chakras. Nadis seem to correspond to the meridians of traditional Chinese medicine.
Nadis are not nerves but rather channels for the flow of consciousness. The literal meaning of nadi is'flow'. Just as the negative and positive forces of electricity flow through complex circuits, in the same way, pram shako (vital force) and manas shako (mental force) flow through every part of our body via these nadis. According to the tantras there are 72,000 or more such channels or networks through which the stimuli flow like an electric current from one point to another
Nadis are thought to carry a life force energy known as prana in Sanskrit, or qi in Chinese-based systems. In particular prana (active) is supposed to circulate inside Pingala, while apana (passive) is supposed to circulate inside Ida. Inside Sushumna is supposed to circulate kundalini when awakened The Ida and Pingala nadis are often seen as referring to the two hemispheres of the brain. Pingala is the extroverted (Active), solar nadi, and corresponds to the right hand side of the body and the left hand side of the brain. Ida is the introverted, lunar nadi, and corresponds to the left hand side of the body and the right hand side of the brain (crossing occurs in the optical chiasma).
These nadis are also said to have an extrasensory function, playing a part in empathic and instinctive responses. The two nadis are believed to be stimulated through different practices, including Pranayama, which involves alternate breathing through left and right nostrils, which would alternately stimulate respectively the left and right sides of the brain. The word nadi comes from the Sanskrit root nad meaning "channel", "stream", or "flow". The rhythmical breathing and special breathing techniques are supposed to influence the flow of these nadis or energetic currents. According to this kind of interpretation (which is the Yoga interpretation) the breathing techniques will purify and develop these two energetic currents and will lead to breathing special exercises whose goal is to awake kundalini.