How to enforce scroll up in a drop down list ?

[mohsen...@gmail.com]

I have a drop down list built with select html tag . I have 10 items in the list. I have two arrow buttons up and down. when the user hits the up arrow the selected item should move up in the list. Currently the item is moved up in the list  but the scroll bar does not move up . How to enforce an update in the scroll bar for the drop down menu when ever I make a change ?