Chakras are the major energy centres of our subtle body. So, there are not only 7 but many other chakras also. However 7 Chakras are considered the main. The refrences of 7 chakras and Kundalini Shakti are in Puranas and Upanishads. Lalita Sahasranama stotra from Brahmanda Purana gives the most precise description of Kundalini in just 3 verses.
मूलाधारैक निलया ब्रह्यग्रन्थि विभेदिनी ।
मणि पूरान्तरुदिता विष्णुग्रन्थि विभेदिनी ।।
आज्ञा चक्रान्तरालस्था रुद्रग्रन्थि विभेदिनी ।
सहस्राराम्बुजारूढा सुधा साराभिवर्षिणी ।।
तडिल्लता समरुचि: षट्चक्रोपरि संस्थिता ।
महासक्ति: कुण्डलिनी विसतन्तु तनीयसी ।।
Muladharaika nilaya bramhagrandhi vibhedini। Manipurantarudita vishnugrandhi vibhedine।। – 38
Aagyna-chakrantaralasdha rudra-grandhi vibhedini। Sahasraranbujaruda sudhasarabhivarshinee।। – 39
Tatillata samaruchi shatchakropari sansdhita। Mahashakti-kundalini bisatantu taniyasi।। – 40
You are the one sitting in the Muladhara, you are the one who pierce the knot of Brahma (Brahma Granthi). You are the one in the Manipura, you are the one who pierce the knot of Vishnu (Vishnu Granthi). You are the one in the Ajna Chakra, you are the one who pierce the knot of Rudra (Rudra Granthi). And reaching in the Sahasrara you rain the Nectar (Soma) / Amrita there. Bright like Lightning you reach above the Six chakras. You are Kundalini the great energy which is subtle in nerves.
Thus from above we can know there are 7 Chakras including Sahasrara chakra. There are three knots called Brahma granthi, Vishnu granthi and Rudra granthi. These knots are formed because Ida and Pingala nadi which are left and Sushumna nadi ties in these Chakra and forms knots. Thus it makes difficult to pass Kundalini from these Chakra. As first knot is itself present in Muladhara so it becomes a bit difficult to Kundalini Shakti to pierce this knot. Brahma knot is present around Manipura and Swadhisthana area. Vishnu knot is present in Manipura and Anhata area. Rudra knot is present in Ajna Chakra area.
Thus Kundalini travels the three great steps from Brahma granthi to Vishnu Granthi, from Vishnu Granthi to Rudra granthi and from Rudra granthi to the Highest place then there nectar flows. This process resembles the story of RigVeda in which Vishnu takes three steps, reaches the highest place in third step and then Soma (Nectar) flows [RigVeda1.32.12]
Other chakras are also mentioned in Lalita Sahasranama from verse no. 98 to verse no. 109.
Chakras are also described in Skanda Purana in the chapter "The Tandava Dance of Shankara ". There it describes how music originated from Chakras. It has also relation with Beeja mantra associated with Chakras.
- Sriraga, the most charming one. is the first son of lsvara. He occupied a seat in the middle of the eyebrows. He is the giver of the supreme Brahman (Parabrahman),
31 In the centre there of is the excellent Gana born of Mahesa. The second (Raga) originated from the waist region. it is Vasanta of great repute.
- Pancama (name of a Raga) is the third one, the ornament of the universe. It originated from Visuddhi Chakra (situated in the inner throat). It is marked by the principle Mahat.
- The Anahata Chakra originated from the heart of Maheswara. The Raga Bhairava which itself is Bhairava (terrible) originated fom the region of nostril.
- This Chakra is named Manipuraka and it is indeed the bestower of salvation. The fifty Varnas (letters) named Anka originated from Maheswara.
- The twelve Rasis (signs of the zodiac) and the constellations originated from Svadhisthana (Chakra) along With the seeds of the universe.
- The organ of generation of Isa gets enlarged in a moment. Then Retas (semen virile) issues forth and the universe is created from the Rents.
- From the Adhara Chakra the great sixth (Raga) named Nata Narayana originated, It is the favourite son of Mahesa. It is Nila (blue in colour) and it has the exploit of Vishu.
- These personified Ragas assisted by their wives (Raginis) originated thus. Their wives originated from the region of the head of the Pinaka-bearing Lord.
The Suta Samhita of Skanda Purana has a separate chapter called 'NadiChakra Nirupana". It deals in details about the position of Nadi and Chakras.
There are about 20 Yoga Upanishads which deal with the description of Nadis and Chakras.
For eg. Hamsa Upanishad (4th verse) says this:
- Now we shall explain the true nature of Hamsa and Paramahamsa for the benefit of a Brahmacharin (a seeker after Brahman or celibate), who has his desires under control, is devoted to his guru and always
contemplates (as) Hamsa and realise thus: It (Hamsa) is permeating all bodies like fire (or heat) in all kinds of wood or oil in all kinds of gingelly seeds. Having known (It) thus, one does not meet with death. Having contracted the anus (with the heels pressed against it), having raised the Vayu (breath) from (Mula) Adhara (Chakra), having made circuit thrice round Svadhisthana, having gone to Manipuraka, having crossed Anahata, having controlled Prana in Visuddhi and then having reached Ajna, one contemplates in Brahmarandhra (in the head) and having meditated there always ‘I am of three Matras’, cognises (his
Self) and becomes formless. The Sisna has two sides (left and right from head to foot). This is that Paramahamsa (Supreme Hamsa or Higher Self) having the resplendence of Crores of suns and by whom all this world is pervaded.
Dhyana Bindu Upanishad:
52-53. Of these, the chief ones are ten and carry the Pranas. Ida, Pingala, Susumna, Gandhari, Hastijihva, Pusha, Yasasvini, Alambusa, Kuhuh and Sankhini are said to be the ten.
54-55(a). This Chakra of the Nadis should ever be known by the Yogins. The three Nadis Ida, Pingala and Susumna are said to carry Prana always and have as their Devatas, moon, sun and Agni.
55(b)-56(a). Ida is on the left side and Pingala on the right side, while the Susumna is in the middle. These three are known to be the paths of Prana.
56(b)-57. Prana, Apana, Samana, Udana and Vyana; Naga, Kurma, Krikara, Devadatta and Dhananjaya; of these, the first five are called Pranas, etc., and last five Naga, etc., are called Vayus (or sub-Pranas).
58. All these are situated (or run along) the one thousand Nadis, (being) in the form of (or producing) life. Jiva which is under the influence of Prana and Apana goes up and down.
Chapter 3 of Yoga Kundalini Upanishad:
8(b)-9(a). Having known Vayu, the above-mentioned Bindu and the Sattva-Prakriti as well as the six Chakras, one should enter the Sukha-Mandala (the Sahasrara).
9(b)-11. There are six Chakras. Muladhara is in the anus; Svadhisthana is near the genital organ; Manipuraka is in the navel; Anahata is in the heart; Visuddhi is at the root of the neck and Ajna is in the head (between the two eyebrows).
12. Having known these six Mandalas (spheres), one should enter the Sukha-Mandala (Sahasrara), drawing up the Vayu and should send it (Vayu) upwards.
13. He who practises thus (the control of) Vayu becomes one with Brahmanda.
There are other superb texts like Hatha Yoga Pradipika, Goraksha Shatakam written by Guru Gorakhnath and other Agama texts which deal in detail about Kundalini Yoga.
This Chapter of Devi Bhagvata Purana consists of very precise description of Chakras and Nadis. It also deals with some minor chakras.
- Pierce, then, the Lingams (the lustrous Svayambhu Âdi Lingam) in the several Chakras above-mentioned and transfer along with it the heart united with the Shakti to the Sahasrâra (the Thousand petalled Lotus). Then meditate the S'aktî united with Sambhu there.
50-51. There is produced in the Vindu Chakra, out of the intercourse of Shiva and Shakti, a kind of nectar-juice, resembling a sort of red-dye (lac). With that Nectar of Joy, the wise Yogis make the Mâyâ S'aktî, yielding successes in Yoga, drink; then pleasing all the Devas in the six Chakras with the offerings of that Nectar, the Yogi brings the S'aktî down again on the Mûlâdhâra Lotus.
- Thus by daily practising this, all the above mantras will no doubt, be made to come to complete success.
Summarizing in Shortcut:
1) There are 7 major Chakras in our subtle body. The final chakra ie. Sometimes Sahasrara is not also counted as Chakra as it is the final destination.
2) The seven chakras are situated in backbone region in subtle body.
3) Muladhara is in perenium area. Swadhisthana is a little bit above it. Manipura is in navel region. Anhata is in heart region. Visuddhi is in throat region. Ajna is in middle of eyebrow region and Sahasrara is in top of head.
4) These 7 chakras are related with various elements as I discuss in my answer here
5) Kundalini Shakti (serpent energy) is situated in Mualdhara chakra in normal condition. Rising the Kundalini from Muladhara and making it go to Sahasrara is the main aim of mystic Yogis.
6) Brahma granthi, Vishnu granthi and Rudra granthi are the knots in the path. They are loosened by other Yogic exercises like Kumbhaka, Rechaka, Puraka and leaving attachment. Brahma granthi loosens by transcending material attachment, Vishnu granthi loosens by transcending emotional attachment and Rudra granthi loosens by even transcending spritual attachment.
7) The path of Kundalini is through the Sushumna nadi, the Ida bearing moon sign being left to it and Pingala bearing sun sign being right to it.
8) When Kundalini pierces Rudra granthi and reaches Sahasrara then it becomes one with it, then the person becomes one with the Universe and attains liberation (Kaivalya).