The Upanishads already treat prana as prior to the other senses: the Prashna Upanishad and Chandogya Upanishad both tell a fable in which speech, sight, hearing and mind each claim to be the greatest of the body's powers, and each in turn withers when prana departs, proving that prana alone sustains the rest. Prana is one word doing several jobs in these texts: the breath itself, the general life force, and also the name of one particular current among five, the pancha vayu, that moves outward through the mouth and nostrils. The other four, apana (downward, elimination), samana (digestive, centering), udana (upward, speech and growth) and vyana (pervading, circulation), divide the body's work between them, a scheme set out fully in Ayurvedic and later Hatha Yoga sources.
Pranayama, restraint of the breath, is the fourth limb of Patanjali's eight-limbed yoga in the Yoga Sutras, and Hatha Yoga texts such as the Hatha Yoga Pradipika treat it as the direct technology for gathering prana and driving it up the central channel, sushumna nadi, through the network of seventy-two thousand nadis the body is said to contain. Where prana is forced into sushumna in sufficient concentration, it is said to rouse kundalini, the dormant coiled energy at the base of the spine, and drive it upward through the chakras. Prana is described as continuous with the universal life force, Brahman acting in the body, so that cultivating it is simultaneously a physiological and a soteriological act, not two separate things.