Alexander the Great not only had a talent on the battlefield (he created a huge empire between 334 and 326 BC) but was also a man who appreciated science and philosophy. A lasting tribute to this is the City of Alexandria, in the modern day Egypt. This city was unique in ancient times as it provided physicians and doctors with opportunities that had hither to been denied. 

In Alexandria was built a massive library that contained the works of all of the greatest philosophers of the day, such as Aristotle and Plato. These men argued that the soul of a person left the body upon death and that, therefore, dissection of the body was permissible. The influence of these philosophers in Alexandria was such that dissection was, for the first time, allowed to happen in Alexandria. This allowed doctors to see the workings of the body and must have led to a greater understanding of physiology. (For a short period of time the dissection of LIVE people, criminals who were condemned to death, was allowed to happen in Alexandria). 

These practices led to the development of theories of a nervous system (Herophilus) which were later developed and tested by doctors such as Erastistratus.