Fundamental TTL circuit and its operation
The TTL gate is in either of two states. If its emitter is high (all of them), Q1 is cut off. Current flows through its B-C junction and turns on Q2, driving the output low.

If any of Q1's emitters is pulled low, then it conducts, pulling the base of Q2 low. There is a small transient current when this occurs, but no DC current. Since the base of Q2 is actively pulled low through a low impedance, it switches faster than it otherwise might.