These two groups of nadis originate along with Sushumna in the Mooladhara chakra and terminate at Agnya chakra. They criss-cross each other at each of the chakras (Fig-2). When Ida group of nerves is active breath in the physical body flows through the left nostril. When Pingala group is active breath flows through the right nostril. Ida is cooling and is also known as Chandra (Lunar) nadi. Ida is feminine and is the storehouse of life producing maternal energy. Pingala is masculine, activating and is known as Surya (Solar) Nadi. Energy either flows in the Ida or the Pingala. When the energy flowing in the Ida or the Pingala is made to flow equally through both these nadis, then the breath flows evenly through both nostrils in the physical body and the energy then begins to flow in the Sushumna. When breath flows through the left nostril mental activities should be done and when breath is flowing in the right nostril physical activities like hard labor should be done. When breath flows equally through both nostrils, meditation will be very good. 
At mooladhara chakra there is a coiled structure a nadi that appears in meditative vision as a coiled snake. In this structure kundalini energy resides. From this coiled nadi the seat of kundalini twenty nadis originate, ten branching upwards and ten downwards. The upward branching nadis are Ida & Pingala ( connected to the nostrils the sense of smell, Sushumna ( third eye), Gandhari & Hastijhiva ( connected to the ears the sense of hearing ); Pusha & Alambusha ( connected to the eyes the sense of sight) Kuhu ( anus), Shankini(sex organ) and Sharada ( mouth). 

Kanda  
This is an important nerve junction in the astral body and corresponds to the cauda equina of the physical body and is situated between the anus and the sex organ in the physical body. The spinal cord extending from the brain to the end of the vertebral column tapers off into a tiny silken thread from the point between L1 and L2 vertebrae. From here it gives off innumerable nerve fibers, crowded into a group. This group of nerves is called cauda equina. It is like the shape of an egg and is just above the mooladhara chakra. All the nadis spring from this center. It is here that Sushumna is connected to the mooladhara chakra. The four petals of this chakra are on the sides of this kanda and the junction is called Brahma Granthi. At this junction the influence of Maya is very strong. 
There is another very big nerve junction from where all the 72000 nadis of the astral body originates or circulates itself. This junction is near the navel. This junction is also referred to as Kanda in ancient texts. 

Granthis  
The word, ‘Granthi' means a knot or an obstacle that is presented in spiritual growth. There are three such knots. 

Brahma Granthi  
This is the first knot and is located at the mooladhara chakra. This knot is connected with the world of names and forms. It creates ambitions and strong, demanding, sensual desires and creates vehement attachment to these. It obstructs the path of the Kundalini and prevents its upward movement. This creates restlessness and prevents the mind from concentrating. Grace of Guru, proper self effort and the grace of the Goddess Kundalini unties this knot.