The three subtle channels are placed within the spine and find their expression in the autonomous nervous system which comprises the left and right sympathetic nervous systems and the central parasympathetic nervous system. The central nervous system represents the consciousness we have achieved in our evolution up to human awareness. Through Sahaja Meditation the central nervous system becomes enlightened with the awareness of our spirit. Thus through this system we can actually feel our spirit manifesting itself to us as vibrations.
The left and right sympathetic nervous systems we use fo our day-to-day physical, mental and emotional activity. Within the subtle instrument, Ida Nadi (see chart: blue channel) manifests the left sympathetic nervous system and Pingala Nadi (see chart: yellow channel) the right.
By-products of Ida Nadi activity create the balloon of superego in the head, beginning on the left at throat level and mostly covering the back and right side of the head. Pingala Nadi activity creates another balloon of ego on the other side covering the front and left side of the head.
The central channel of the Sushumna Nadi (see chart: center channel) manifests the parasympathetic nervous system. This system is self-governing. The self of spirit witnesses the action of the parasympathetic system which controls our involuntary activities such as heart beat, breathing and reflex, that is, unconscious as opposed to conscious activity. Although we can to a degree control our sympathetic action, for instance we can make our hearts beat faster, we cannot consciously slow the heart down, which is parasympathetic action.
Here you can read more details about the three channels:
The Self existing at this level means that we cannot achieve Self-Realization through our own effort but only through connecting to the All-Pervading Power by awakening our inner energy. Spirit is spontaneous, as natural and vital to us as our heartbeat. How long would we last if it were only our will that kept our hearts beating, or if we were to learn breathing from a book? The Spirit is infinite. Only our Inner Energy (Kundalini) can bridge that great divide between illusion and reality.