Kundalini System:
Kundalini (Sanskrit: कुण्डलिनी kuṇḍalini, "coiled snake") is a form of divine feminine energy Shakti (universal dynamic force) located at the base of the spine, in the Muladhara (1st chakra) region. Yoga focus is on awakening kuṇḍalini through meditation, pranayama breathing, the practice of asana, visualization, prayer and chanting of mantras, guru yoga, austerity and virtue. Also, it can be awakened by Shaktipat (as experience, via spiritual transmission by a teacher).
When kundalini integrates with prana it starts rising and needs to be directed upward. Within kundalini the contact is made between the mystical Infinite Divine Energy of Consciousness (Lord Shiva*), and the mystical Divine Energy of Creation (Goddess Shakti**). To gain the highest spiritual potential, the great mass of kundalini energy locked in the root chakra must be released to travel through all seven chakras, up the main channel called Sushumna to the crown chakra.
Sushumna is a central channel (a nadi) in the spinal column to which prana is directed. Other two important nadi (among 72,000) called Ida and Pingala, they run parallel to Sushumna, on the left and the right sides.
Besides the main seven chakras there are numerous other energy centers within our bodies. The system of chakras, together with prana, kundalini, nadi (energy channels) and bindu (drops of essence) are components of an esoteric description of the "subtle body".
From the biological perspective the kundalini awakening is a complex physio-psycho spiritual transformative process, where "central channel" (dbu ma or avadhuti) is the arterial system, or more specifically the aorta. The two "side channels" are the venous system (roma or rasana), and the spinal column and nervous system (rkyang ma or lalana). On the physical level Pingala has its counterpart in the parasympathetic nervous system, Ida in the sympathetic nervous system, and Sushumna in the central nervous system. A chakra is any place in the body where there are clusters of arteries, veins and nerves.
It is believed that prana is a type of astral energy, which science calls "dark energy/matter", beyond quantum type, undetectable by scientific instruments, but observable via the effects of gravitation. It is an intelligent energy, it can be directed by our will and thoughts, breath, asana, mudra, sound and visualisation.
NOTE: Kundalini energy is a very powerful force, and scientifically very little understood subject. It is very real and can be accessed with practice, as well as manifest uncontrollably and spontaneously. It can be dangerous. Go slow, study, and be very cautious before proceeding to practice any pranic breathing exercises. Experience shows definite need for many years of dedicated yoga practice in order to be able to begin to handle and integrate this spiritual energy. Careful purification and strengthening of the body and nervous system (with yoga and meditation), as well as overall spiritual development (strong philosophical basis, reliable faith, proven path, trustworthy source, solid lineage, diligent guru, learned lama, accomplished teacher, wise mentor) are required beforehand.
In the East, in the ancient times, this knowledge was made into science and taught at universities, but over time mostly eradicated, forgotten, partially lost, hidden, and/or reserved for a few fortunate, dedicated ones. There's very little reliable information, and in society at large there's little interest in these subjects. Some of it is very difficult to understand, accept and practice.
Now, even in India where this knowledge originated, there's a lot of confusion, misunderstanding, fake guru, and ignorance on this subject. There are real lineages and gurus operating in the West today, but you'd have to find them for yourself. If you're lucky you may connect to one right away, or it may take a lifetime of searching. Look for a large variety of trusted, solid, respected, tested, and balanced teachings and teachers. Don't just put all your trust in one guru or a system, use common sense and your intuition, follow your heart, learn, try, test.
Pray for blessings of the Divine Father* who resides within as consciousness and knowledge, and the Divine Mother** who lives within as energy and vitality. May they always take care, protect and guide, and in their infinite love lead to cosmic consciousness.
Om Namah Shivaya (ॐ नमः शिवाय; "O, Salutations To The Auspicious One!", Adoration To Lord Shiva, "Universal Consciousness Is One")
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* Lord Shiva or Purusha, pure consciousness, unchanging, unlimited observer, masculine, paternal love of God.
** Goddess Shakti or Prakriti, Adi Shakti or Adi Para Shakti, primordial energy, Divine Mother, Creatrix, feminine, motherly love of God.