It is not haraam to draw such pictures for purpose of education through illustration. The intent of the Law for prohibiting images was that in the pagan times, it was a direct means and way to shirk (association of partners with Allah). In other words, these things were forbidden only because they served as direct means and avenues to shirk; and therefore where there are not even the remotest possibilities of shirk, there is no reason to consider it as haraam, especially if there are tangible benefits in them. Mind you, today it has become a most powerful medium of communication. So Muslims cannot simply afford to neglect this vital medium of communication; if they do, they only do so at their own peril. Therefore, as long as you are drawing pictures for purpose of education or as a medium of communication there is nothing to consider it sinful or haraam (forbidden). May Allah help us to see the intents and purpose of the Divine Laws and thus practice them with understanding-aameen.