I definitely saw something like the 'button' I described.
Or after another thinking, it might be the buttons on the two sides of the 'scrollbar'.
If you don't know what I am talking about, please open the Matlab help window. There is a scrollbar on the righthand side. There are two buttons at the top and buttom of the scrollbar with small arrows. If you press one of these two buttons and hold it, the text in the help window will scroll down.