It is amazing to know that the enlightened Rishis have given us the structure of Astral body , which is suppose to be replica of the physical body , so well that it fits in to our understanding of the anatomy of the human body. These thing were described in scripture written many thousands of years ago.
The astral body has a spine , just like the physical body . It has 3 coverings just like the physical body. The human spine is covered by 3 layers, the outermost is Dura matter, the middle one is the Arachnoid and the innermost is Pia matter.The human body has the brain-cerebrum then the spine with it's cervical dorsal , lumbar , sacral and coccygeal parts and then the nerves. similarly the astral spine has these parts called Chakras, and their extension called the nadies. ( According to Scriptures there are 72000 nadies. ) The Astral body is the source of power to the 5 'dnynedriyes' (organs of the perception ) and 5 Karmendriyes (organs of the action ) and stores the 'impressions ' in 'abstract ' forms which are called "Saunskar " . It provides energy or powers by 5 Pranas which in human body manifest as crystallisation circulation , assimilation ,metabolism and elimination, As mentioned the astral body is made of 24 principals .The Astral spine is called 'Sushumna' and it extends from coccygeal center( Muladhar chakra ) to the brain . This is the one which is the source of the energy . Within the Sushumna are 2 other astral spines called "Vajra " and the " Chitra " The Vajra extends from sacral area or the Swadhishthan chakras upward to the brain . The Vajra allows the astral spine to 'move ' or 'expand ' or ' contract '. On the other hand the Chitra is the source of "consciousness " or the spiritual activities . In the human body there is ' sympathetic ' and 'parasympethetic ' activities . These are responsible for the things which are not under our will . e.g heart rate the blood pressure or the activities of the intestines etc . These sympathetic chains run on the sides of the spine . In the Astral body this is represented by 2 chains called 'Ida ' and the 'Pingala '.
The causal bod is the 'thought ' behind the whole human body and is called "Brahmanadi "
PLEASE NOTE THAT THIS WHAT I UNDERSTAND AND NOT EXPERIENCED .