Yes, I agree with tthorst. You definitely want to make sure that your essay has everything that you want to relay. I think that it is a huge advantage to have no type of word limit. You can have the opportunity to really explain your desire to attend the school. And that is exactly what it is--an opportunity, so you should take advantage of it. I advise that you don't write an novel, but don't be shy to make sure it is clear why you want to go to Meharry.
Best of Luck