Nadis

Nadis are subtle energy channels, similar to meridians in Chinese Medicine. James Bailey describes them as ‘our energetic irrigation system…Some are wide and rushing, others are a mere trickle. When this system flows freely we are vital and healthy; when it becomes weak and congested, we struggle with poor physical and mental health.’[1]

According to tantric texts, we have 72,000 nadis, although the main three are the most accessible.
Sushumna runs directly up the spine, allowing a flow of energy between the chakras. It is criss crossed by ida and pingala, intersecting at each of these junctures.
Ida flows thought the left nostril, it relates to moon side of our nature, our creative, empathic, cooling, soothing and nurturing side.
Pingala flows through the right nostril, relating to the rational, practical, dynamic, vigorous and vital sides of ourselves- our ‘sun’ side.

‘The interaction between ida and pingala corresponds to the internal dance between intuition and rationality, consciousness and vital power, and the right and left brain hemispheres… Bringing ida and pingala into equilibrium is a major focus of hatha yoga—so important, in fact, that the term hatha symbolizes this balance.’[2]

Image: http://kriyavansinlove.blogspot.com.au/2010/11/bhagavad-gita-344-karma-yoga-yoga-of.html