Sushumna
The most important and fundmental forms of energy enter the human system through the Root and Crown chakras. These two chakras are connected by a nadi called, sushumna.

The sushumna runs up and down the central axis of the body within the spine, between the crown (top of the head) and sacrum. The sushumna is also connected to all seven primary chakras via the "stems," which provides each chakra with this vital energy.

This primary current runs "between the sun and earth" - "from heaven above and earth below."

As Above, So Below.