nervous system
Reason #3: "Just like the roots of a tree begin as small individual roots spread over a wide area, your nervous system begins as individual cells called neurons that are spread all throughout your body."
The rest are in the link.
"In yoga, the human nervous system is like a set of antennae that can focus and channel the creative power of the universe into expression in a single life. Pranayama practice polishes the capacity of the nervous system to conduct this cosmic creative potential into real, tangible manifestation."
"The nervous system is like two sets of one-way streets Through one set of nerves, the sensors tell the brain what they sense Through another set of nerves, the brain tells the muscles to contract and cause the body to move."

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