How many chiral carbons are there in reserpine ? Kindly explain and mark the centres in the diagram

Reserpine is an alkaloid extracted form a plant called Rauwolfia serpentine. When consume in minute quantities it may act as antipsychotic and antihypertensive drug. 
The complex structure of the mentioned drug is as follow:-

It contain only 6 chiral centres or chiral carbon, which are clearly visible in the above structure.