One of the keys to experiencing the restorative power of yoga practice is consciously turning the sense powers that normally move outward to interact with the world around us back into ourselves. This is the practice of Pratyahara, the withdrawal of the senses.
When the senses turn inside they are said to rest back in their source. Just as we recharge our devices by plugging them into a power source, similarly, in practice we plug our awareness into its power source inside. In this way, our sense perceptions emerge restored, recharged and with renewed clarity.
This source power that enlivens and sustains the senses is the Prana Shakti. Prana is the animating, vitalizing power of consciousness.
I love this story from the Upanishads in the form of a Q&A that illustrates the relationship of the senses to the Prana:
“Holy Sir, how many several powers hold together this body? Which of them are most manifest in it? And which is the greatest?”
“The powers,” replied the sage, “are ether, air, fire, water and earth – these being the five elements which compose the body; and, besides these, speech, mind, eye, ear, and the rest of the sense organs. Once these powers made the boastful assertion: ‘We hold the body together and support it,’ whereupon Prana, the primal energy, supreme over them all, said to them: ‘Do not deceive yourselves. It is I alone, dividing myself fivefold, who hold together this body and support it.’ But they would not believe him.
“Prana, to justify himself, made as if he intended to leave the body. But as he rose and appeared to be going, all the rest realized that if he went they also would have to depart with him; and as Prana again seated himself, the rest found their respective places. As bees go out when their queen goes out, and return when she returns, so was it with speech, mind, vision, hearing and the rest. Convinced of their error, the powers now praised Prana, saying: ’As fire, Prana burns, as the sun, he shines; as cloud, he rains; as Indra, he rules the Gods; as wind, he blows; as the moon, he nourishes all. He is that which is visible and also that which is invisible. He is immortal life.’”
From: Upanishads, Breath of the Eternal, by Swami Prabhavananda and Frederick Manchester (translators)