"I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world."
--ALBERT EINSTEIN
Your first task is to decide what you want to accomplish in your talk. I think you should try to help the teachers with their job. Their job is to get students interested in learning something about how the brain works, and then to convey the most elementary information to the students.
The best thing you can do for the teachers is to have them leave your lecture with a lesson plan in their heads. Give the teachers material that they can present to their students in a class period.
Don't presume ANY prior knowledge of the subject. While you can presume the audience understands "brain" and "spinal cord," even simple terms like "axon," "neuron," "spike," etc., while likely to be recognized, are probably only vaguely defineable by the teachers. Don't presume ANY prior interest in the subject.
A large part of your talk, especially at the front end, should be motivational. Taking up to half your time to get the audience interested in the topic is not excessive. However, avoid pablum (introductions that convey no information); interesting facts, problems, history, anecdotes, clinical cases, etc, are the best motivators.
When I do general talks, I bring a wet and dripping brain (with Formalin) which I pass around. Nothing awakens interest faster. Some brain slices to show the insides (especially the cerebellum) are also wonderful.
Related to the above: the most common mistake of science teachers is to try to "cover material." There are lots of good books available with all the information anybody would want. If they get interested enough in your lecture, they will find out what you didn't have time to cover. Stick to the most fundamental topics you can think of.
What should a High School student know about the Institute for Advanced Absurdity?
