Prashna Upanishad 71.3

71.3

āsu nāḍīṣu vyāno vāyuḥ carati vyāno vyāpanāt /
ādityādiva raśmayo hṛdayāt sarvagāminībhirnāḍībhiḥ sarvadehaṃ saṃvyāpya vyāno vartate /
sandhiskandhamarmadeśeṣu viśeṣeṇa prāṇāpānavṛttyośca madhya udbhūtavṛttirvīryavatkarmakartā bhavati //6//

Hi eṣaḥ ātmā, this Self—this subtle body associated with the Self—is in fact; hṛdi, in the heart, in the space circumscribed by the lump of flesh shaped like a lotus. Atra, in this heart; there are etat ekaśatam, this one hundred and one, in number; nāḍīnam, from among the nerves, among the chief ones. Tāsām, of those chief nerves; ekaikasyāḥ, each one has; śataṁ śatam, a hundred divisions. Again, prati śākhānāḍī-sahasrāṇi, the thousands of sub-branches into which each of the (one hundred of) branch nerves is sub-divided are, in each case; dvāsaptatiḥ, dvāsaptatiḥ, seventy-two, seventy-two. Each of the hundred branches of the main nerves becomes (seventy-two) thousand in number.footnote{To sum up: There are 101 main nerves; each is divided into one hundred branches; and each of these branches is sub-divided into 72,000 sub-branches. Thus the sub-branches are 727,200,000 and the total number of all the nerves is 727,210,201.} Āsu, among these nerves; carati, moves; the vital energy called vyānaḥ, Vyāna, the name being derived in the sense of pervasiveness. As rays issue from the sun, so do the nerves issue from the heart and proceed everywhere (in the body); moving through them Vyāna resides in the body, pervading it wholly; and by becoming particularly active in the joints, shoulders, and vital parts, and in the interim between the functioning of Prāṇa and Apāna, it becomes the performer of deeds requiring strength.