Anatomy teaches us that there are nerve centres and nerve fibres all over the body. To the naked eye a difference is obvious between certain portions of the brain and spinal cord, viz the grey matter and the white matter.
The grey matter is largely composed of nerve cells, while the white matter contains only their long processes, the nerve fibres.
Yoga sadhana is helpful to control our nervous system?
In the Yoga Sadhana of Siddhis, an effort is made to gain control over this System of nerve cells which pertain to “Annamaya-kosha” (physical body) and “Pranamaya-Kosha” (psychological sheath).
It is the grey matter that nervous im- impressions and impulses originate and the nerve fibers conduct these impulses.
Hence the functions of nerve cells are consciousness. There are two systems of nerve cells and fibres in the body viz, cerebrospinal and Sympathetic Systems. The Sympathetic System of cells apparently have no consciousness.
The functions of the body such as digestion, exertion, peristaltie action of the intestines are governed by this Sympathetic System, which are not normally under the control of the will.