Negative feedback restores systems to their original level. The possession of separate mechanisms involving negative feedback controls departures in different directions from the original state, giving a greater degree of control. Positive feedback results in greater departures from the original levels. Positive feedback is often associated with a breakdown of control systems, e.g. in temperature control. Candidates should be able to interpret diagrammatic representations of negative and positive feedback.

A feedback is when a receptor senses a change in stimuli due to a response that it coordinated. This means that it can make an informed decision to change the response it is coordinating.

Negative feedback is when feedback makes the response stop.

There is a norm for conditions, and if this is deviated from in either direction a different response will be coordinated. A response in either direction (if there is too much or too little of something) will have its own negative feedback loop. For example, the alpha cells stop producing glucagon when the blood glucose concentration is back up to normal, and the beta cells stop producing insulin when the blood glucose concentration is back down to normal.

Positive feedback is when feedback makes the response carry on, making the conditions get further and further from the norm. One example of this is in neurones when sodium is detected sodium ion channels are opened so more can flood in.

Mostly positive feedback is a bad thing caused by a disease or due to a break down, for example hypothermia.