HT1338: OS X: Updating OS X and Mac App Store appsLearn about OS X: Updating OS X and Mac App Store apps
Currently Being ModeratedFeb 27, 2013 6:47 PM (in response to rwc)
Check System Preferences -> Keyboard -> Keyboard tab -> [_] Use all F1, F2, etc. keys as standard function keys.
If "Unchecked" you should have your sound, brightness keys back.
If it is already unchecked, check it exit System Preferences, then uncheck it. That could reset things.
Finally as an experment try holding the 'fn' key while pressing the brightness or sound keys.