Kranthi Kiran's

 

There are six Chakras. Muladara is in the anus.Svadhishthana is near the genital organ. Manipura is in the navel. Anahata is in the heart.

The Vishuddhi Chakra is at the root of the neck. The sixth Chakra, the Ajna is in the head (between the two eyebrows).

After gaining a knowledge of these six Mandalas or spheres, one should enter the Sukhamandala, drawing up the Vayu and sending it upward.

He become one with Brahmanda, the macrocosm, who practices thus the control of Vayu. Vayu, Bindu, Chitta, and Chakra should be mastered by him.

(Yoga-Kundalini Upanishad)
The junctions of Nadis with Sushumna Nadi are known as Chakras, subtle centers of vital energy.
Chakras (wheels or circles) or Lotuses are the dynamic Tattwika (Tattwa means Element), centers in the body, they are situated in various point of Sushumna (spinal cord). They are all supported by the vertebral column; the five regions of the spinal column (coccygeal, sacrum, lumbar, dorsal and cervical region) correspond with the regions of the five Chakra : Muladhara, Svadhishthana, Manipura, Anahata and Vishuddha.
All the functions of the body are under the control of the Chakras in Sushumna.
The Chakras are centres of Pranashakti, Shakti as cosmic energy in latent shape, the presiding Devatas of which are the names for the Universal Consciousness as it manifests in the form of these centres.
A particular Tattwa (Element) preponderates at every Chakra.
In every Chakra a certain animal is represented. It denotes that the center has the qualities, Tattwas or Gunas of that particular animal.
Some Hatayogis say that there are 21 minor Chakras beside the 13 major Chakras, others say that there are 49, while the ancient Yogis taught that there are 144 Chakras.
"The term "Shat-Chakras" refers only to the chief six Chakras, viz., Muladhara, Svadhishthana, Manipura, Anahata, Vishuddha and Ajna. Above all these we have Sahasrara Chakra: this is the chief of all the Chakras. All the Chakras have their intimate connection with this center. Hence this is not included as one among the Shat-Ckras. This is situated above all the Chakras." (Sri Swami Sivananda)
Each Chakra has a particular number of petals with a Sanskrit alphabet on each petal. All the 50 Sanskrit letters are on the 50 petals of the six Chakras. The letters exist in the petals in a latent form. These can be manifested and the vibrations of the Nadis felt during meditation. Chakras are in the Linga Sarira (Astral Body), and cannot be seen by eyes, one can feel and understand the Chakras during concentration and meditation only. Sukshuma (subtle) Prana (vital force) moves in the nervous system of the Linga Sarira. Stoola Prana moves in the nervous system of the gross physical body.
"The number of petals in each Chakra is determined by the number and positions of the Nadis around the Chakra.From each Chakra a a particular number of Yoga Nadis crop up. The Chakra gives the appearance of a lotus with the Nadis as his petals. The sound is produced by the vibrations of the corresponding Sanskrit letter. The Chakras with their petals hang downward when Kundalini is at the Muladhara Chakra. When it is awakened, they turn Toward Brahmarandhra. They always face the side of Kundalini."