Prana is the vital energy present everywhere in the Universe. Prana can be looked from two perspectives -
Cosmic Prana - This is the eternal cosmic energy. The whole universe is as a result of the vibrations of the cosmic prana. The manifested vibration is what we see as gravitation, heat and electricity
Individual Prana - This is the vital energy in each individual. All the sensations we experience are due to vibrations of this prana. In 1/1000 th of a second, if there are four billion of vibrations of ether, then our eye would see red color, skin feels 31 degree centigrade, and ears hear 'e'.
Finest manifestation of vibrating prana is mind and the grossest is the body.
The Pranic energy in stored in the Spinal Region. There are various nerve centers in the Spinal column from which originates all the motor and sensory nerves all across the body. The centre which regulates respiration is opposite to the thorax. This centre controls other centers. The aim of Yoga is to control this centre called Plexus. There are 3 centres below this and two above the brain.
The Pranic Energy causes the movement of the diaphragm and the movement of lungs. Controlling the movement of lungs and the diaphragm helps us gain control on the pranic energy.
All parts of the body are connected to the brain through nerve currents which causes motion in the body.
These currents can be viewed of two types -
Afferent Currents - from body to brain - passes through Ida which is the right channel in spinal cord
Efferent Current - from brain to body - passes through Pingala which is the left channel in spinal cord
The health condition of the body is the result of the normal activities of this vital energy. when this life force acts freely, there is no scope for any diseases in the body. When we make this vital force action perfect, we can recover from any injury or disease.
In between the two nadis (Ida and Pingala), there is a channel in the centre called Sushumna. The Yogis after reaching the higher states, can pass the nervous currents through the Sushumna. When this happens, the mind vibrates at the highest degree producing a new superconscious state.
Yoga Its Theory and Practice - Swami Abhedananda