short run - behaves simply, equilibrium at intersection of 2 curves  

• natural level of output (Yn) doesn't come into play in short run
• equilibrium at instantaneous intersection of AS and AD relations

medium run - shift back to natural level of production  

• over time, AS adjusts to go back to natural level of output
• in this case, output too high >> price higher than expected price
• firms will raise their expected price over time, until AS relation shifts to where the intersection is at Y_n

• in this case, output too low >> price lower than expected
• firms will lower their expected price until AS relation shifts down to where intersection is at Y_n
• important to note that change expected price doesn't shift the AD relation