Human subtle system
The diagram in the picture shows the “subtle system” that we all have inside. This is an ancient diagram of our sympathetic and parasympathetic nervous system, depicted in India long before the advent of western neurology.
Our subtle system is formed by three channels and seven chakras.
At the bottom of the spine, in the triangular bone called “sacred bone” resides a sacred energy called Kundalini.
We use to say that the Kundalini sleeps until She gets awakened. At that moment, She rises alongside our spine, passing through the central channel, up to the top of our head in correspondence of the fountanelle bone, where She connects with the all-pervading Divine energy and this union is called Yoga (yoga in sanskrit means union).
In the past, those who want to reach this state needed to purify all their chakras, so that finally Kundalini could rises spontaneously; it was a hard task that could require a whole life (or many lives). Usually they needed to abandon family and everything to lead an ascetic life.
Now this is no more necessary, because Kundalini can be awakened through meditation and afterwards it is the Kundalini Herself to help us to purify our chakras.