Atman and Paramatman
Atman is not some structure of the organism. Atman is a general term denoting the Main Essence of man. In the literal translation, Atman means non-darkness, that is light. Atman is Brahman: the subtlest Divine Fire-Light, Divine Consciousness acting in the Creation. Sometimes the term Atman is used to denote the Creator in His Abode. There is also the Atmic energy called kundalini; one has to become acquainted with it in order to learn to merge with the Atmic Consciousness .
There is also the word Paramatman — the Highest Atman, i.e. the Atman of the Absolute. It is the Creator.