This video. It is an illustrated model of an axon terminal that is derived by carefully studying rats' nerve ends. The video is half way down the article. You are going to want to use the pause button. Also, if like me, you will probably need wikipedia handy. Enjoy.
In the spirit of the blog, it is unacceptable that any 18 year old (or any adult) does not have a general understanding of what they are looking at in this video. That speaks both to our level of education, but also to our style of education. Every student should understand what the hippocampus is as readily as they understand what a hippopotamus is. There are probably brain mechanisms, emotional responses for one, that make it easier to think about other large mammalian, possibly dangerous entities as opposed to more theory- laden, very small entities, but these are the kinds of things we have to ignore to a great degree, that we have to work around.