It is not haram to draw such pictures for the purpose of education through illustration. The intent of the law prohibiting images was that in pagan times, it was a direct means and way to shirk(associating other beings with Allah).
In other words, these things were only forbidden because they served as direct means and avenues to shirk. Therefore, if there is not even the remotest possibility of shirk, there is no reason to consider it as haram, especially if there are tangible benefits in drawing them.
It is important to keep in mind that today drawing has become a very powerful medium of communication. For this reason, 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 the purpose of education or as a medium of communication there is no need to consider it sinful or haram (forbidden). May Allah help us to see the intents and purpose of the Divine Laws and thus, practice them with understanding. Ameen.