[[Image:Hysteresis.png|thumb|300px|left|'''A graphical depiction of [http://en.wikipedia.org/wiki/Hysteresis hysteresis].''' Arrows indicate the direction of movement from one state to another. For a system that exists in the low output state initially (red line), a relatively high level of input is required to induce a change to a high system output. For a system that exists in the high state initially (blue line), a relatively low level of input is required to induce a change to a low system output. In other words, more extreme amounts of input are required to move out of a state than are required to move into a state (meaning that the system resists a change of state).]]  

[[Image:Hysteresis design.png|thumb|300px|left|The biological design of hysteresis.]]