When the sense organs receive impulses from the external world, they have to deliver these impulses to the mind. This is done through the nervous-bital sheath of the mental being. This provides a linkage between the physical body and the inner self-awareness of the mental consciousness. This same nervous sheath works to carry the reactions of the inner awareness into action to the organs of action. The nervous energies get excited by the impulses coming from either direction. Almost all of the reactionary state of mind comes from the excitation of this vital nervous being and habitual patterns of reaction become ingrained in these channels, creating what most consider to be their individuality or personality, but which in reality is simply a temporary bundle of habits that can be observed and change at a certain stage of the spiritual development by a conscious mentality or higher spiritual focus.
Swami Vivekananda in his Raja Yoga lectures spends a considerable amount of time focusing on the psychic prana, which is the term given to this nervous-vital segment of the mental sheath, and the methods used by the practitioners of Raja Yoga to gain mastery over the reactions that occur at this level, and which tend to otherwise dominate the body and mind’s reactions to events and forces.
Sri Aurobindo describes the action thus: “This nervous mentality pursues indeed all the action of the inner instrument and seems often to form the greater part of things other than sensation. The emotions are especially assailed and have the pranic stamp; fear is even more of a nervous sensation than an emotion, anger is largely or often a sensational response translated into terms of emotion. Other feelings are more of the heart, more inward, but they ally themselves to the nervous and physical longings or outward-going impulses of the psychic Prana.”
“Still the proper action of the sensational mind is not emotion, but conscious nervous response and nervous feeling and affection, impulse of the use of physical sense and body for some action, conscious vital craving and desire. There is a side of receptive response, a side of dynamic reaction. These things get their proper normal use when the higher mind is not mechanically subject to them, but controls and regulates their action. But a still higher state is when they undergo a certain transformation by the conscious will of the spirit which gives its right and no longer its wrong or desire form of characteristic action to the psychic Prana.”
Sri Aurobindo, The Synthesis of Yoga, Part Four: The Yoga of Self-Perfection, Chapter 5, The Instruments of the Spirit, pp. 622-623