prANa is Consciousness in motion. The prANamayakosha is the sheath immediately interior to the annamayakosha (the sheath of food that is the gross physical body) and in sAdhanA it is experienced through consistent practice of prANAyAma. Even in everyday life one might experience the coursing of prANa through one's limbs after vigorous exercise, but for those not yet attuned to prANa it might be experienced as just feeling 'pumped up'. Similarly caffeine can also stimulate prANa in the same way. However, neither vigorous exercise or caffeine intake are systematic ways of understanding and regulating the flow of prANa. On the contrary, that kind of uncontrolled overstimulation of prANa is detrimental because it rapidly ages both body and mind. Therefore, yogis of yore who developed the science of Yoga, laid out the systematic way to regulate, lengthen and control the flow of prANa through prANAyAMa. While some approaches to yoga might focus more on extending life in the body through the lengthening of prANa, in the integrated approach to sAdhanA that combines Yoga, vedAnta and tantra, it is recognized that the prANAmayakosha is only another sheath to be traversed on the way to realize the true Self. So what is required is an understanding of prANa in the context of Self-Realization.
prANa is so named because prANa = pra (first) + ana (eater), which tells us that prANa is the first eater of food. In the Upanishads prANa is called the first eater of food, where by food is meant the mind (rayI). In the tAntric text Shiva Svarodayam, prANa is associated with the sun and it feeds on the mind that is associated with the moon. Here the sense in which the word prANa is used is not restricted to prANa vAyu (breath) alone, but it refers in general to Consciousness in motion that flows through the mind and sense organs to apprehend the external world. However, prANa vAyu is also sometimes referred to as prANa because it is the chief among the five principal prANAs viz., prANa, vyAna, apAna, samAna, udAna. Indeed, prANa is first and most easily experienced through the breath.
prANa vAyu operates in the chest area and is primarily responsible for the intake of prANa through the breath. vyAna is responsible for the circulation and distribution of prANa throughout the body. apAna is that which removes or takes away prANa from the body and is associated with excretion and ejection. samAna vAyu is associated with digestion, while udAna vAyu is the upward rising of prANa that can be used for speech or the upward motion of spiritual energy. It is important to realize that the prANa-s are not associated purely with the intake, digestion, circulation and ejection of material food as described in Ayurveda, although this is how they are first experienced. In fact the more important function of prANa has to do with how it ingests, digests, circulates and ejects mental food. All the sensory inputs and things we read and see through the mind are food for the prANa. This is why in the MuNDaka, MANDukya and Prashna Upanishads we find a shAnti mantram that says:
Om bhadram karNebhih shRNuyAma devAh
bhadram pashyema akshabhiryajatrAh
Om, O gods (who are the deities of the sense organs)
may we hear auspicious things with the ears
may we see auspicious things with the eyes
The sAdhaka realizes that first one should provide useful and auspicious inputs to prANa. Then the digestion of this 'food' is easy and productive of thoughts that lead to spiritual attainment. Often we find that if our mind is wrestling with some unpleasant and difficult thoughts it affects our digestion of material food as well. This is not a surprise since samAna vAyu is being taxed excessively. It is useful to cultivate samAna vAyu that can digest any input, and eject useless inputs. Those who have difficulty letting go of negative thoughts will benefit by strengthening apAna vAyu. Finally one realizes that the purpose of all the prANa-s is to direct the mental effort upwards through udAna and not waste it through excessive and unnecessary speech.
The breath plays a vital role in sAdhanA. SwAmi RAmA calls breath and mind the twin laws of Life. This is a beautiful way of stating this fundamental connection that is extremely useful for the yogi. As SvAtmArAma says in the HaTha Yoga PradIpikA
pavano badhyate yena manastenaiva badhyate
manashca badhyate yena pavanastena badhyate (HYP IV.21)
He who binds the breath, binds the mind.
He who binds he mind, binds the breath.
Thus mind and breath are indeed the twin laws of Life. In the following two verses SvAtmArAma notes
hetudvayam tu cittasya vasanA ca samIraNah
tayorvinashta ekasminstau dvavapi vinashyatah (HYP IV.22)
The two causes of the mind are vAsanas and breath. When one perishes, both perish.
mano yatra vilIyate pavanastatra lIyate
pavano lIyate yatra manastatra vilIyate (HYP IV.23)
The breath dissolves when the mind dissolves.
The mind dissolves when the breath dissolves.
These verses emphasize to the aspirant that one of the easiest means to gain control of the mind is through controlling the breath. Hence, the great importance of prANAyAma. Advanced masters such as BhagavAn SrI RamaNa MahaRshi did not need the practice of breath control so they advocate directly controlling the mind. In my opinion, direct control of the mind is not easy for most sAdhakas. The HaTha Yoga PradIpika goes so far as to emphasize the supremacy of the breath by stating:
indriyANAm mano natho manonAthastu mArutah
mArutasya layo nAthah sa layo nAdamAshritah (HYP IV.29)
The mind is the lord of the senses, but the breath is the lord of the mind.
Laya is the lord of the breath, and that laya rests in nAda.
Once prANa vAyu is well controlled through prANAyAma, then several other aspects of the prANamayakosha are directly revealed to the practitioner. prANa flows in channels that are called nADI. Depending on the source text, the total number of nADI-s is listed as anywhere up to 72,000. Certainly many nADI-s can be directly experienced in the course of practice. However, the most important nADI-s are about ten, as listed in the Shiva Svarodayam. Of these, the knowledge of three is of paramount importance to the sAdhaka. These are:
iDA: the nADI that terminates in the left nostril that carries the lunar (cooling) breath
piNGala: the nADI that terminates in the right nostril that carries the solar (heating) breath
suShumnA: the central nADI that usually does not carry prANA until kuNDAlini is about to be awakened
The nADI-s intersect at junction points called marma-s. The radiate outward from central wheels called cakra-s. The nADI-s are not the nerves, although they are frequently misinterpreted as such. The nADI-s do not exist in the physical plane and therefore they cannot be observed directly by the outgoing senses of sight and touch.
Through the yogic practices of Asana, prANAyAma and pratyahAra, the aspirant can experience prANa in progressively stronger and increasingly direct ways. In Asana the grosser prANas are stimulated and then brought to a state of calmness. In prANAyAma, the subtler prANAs that ride on vAyu are again stimulated and brought to rest. In pratyahAra the prANA-s are withdrawn from the sense organs by directing the mind to a point of focus that leads to dhAraNa.
prANA is likened to the steam that comes off a pot of boiling water that is kuNDAlini. The practices of Asana, bandha and mudra that are given in the HaTha Yoga PradIpikA are directed towards awakening kuNDAlini that then gives the yogi direct knowledge of the microcosmic prANa. Through the systematic practice of shakti calana and stable rising of kuNDalini, the yogi then becomes aware of the macrocosmic prANA, or HiraNyagarbha. This is the prANA that the Upanishads speak of. Then the yogi becomes sensitive to the diurnal cycle of prANa that flows from the sun and the cooling effect of the moon. The movement of the locus of Consciousness within the body as the states of waking, dream and sleep are traversed then becomes clear. Then is also understood the true meaning of the samudra manthan (churning of the ocean), which is nothing but the way the Cosmic prANa flows through the individual and churns the milk inside the human being. Then another facet of the identity of brahmANDa and piNDANDa becomes clear. Then the timing of swara (breath) with the bright and dark lunar fortnights that is detailed in the Shiva Svarodayam is also directly experienced.