What is the difference between negative and postive feedback?

Question

What is the difference between negative and postive feedback?

Answer 1

Negative feedback suggests no helpfull information at all.  Positive feedback should suggest more genuine information.

Answer 2

Say you have a sequence of molecules in a signaling pathway: the initial release of X causes the production of Y which eventually results in the production of the final product of the pathway Z. So X --> Y --> Z

In negative feedback, Z would inhibit the release of a molecule before it, like X. This would mean that once enough Z is produced, eventually, it would stop the release of anymore X, and thus stopping any further production of Z. This type of feedback is often used to reach a balance of a certain molecule. Once the amount of Z falls beneath a certain level, maybe because it is degraded or used up, it can no longer inhibit X, and so more Z will be produced, bringing its levels back up again. An example of this is the thyroid hormone pathway.  In this case X is called TRH, Y is called TSH, and Z is called T3/T4. So TRH-->TSH-->T3/T4. TRH stimulates the production of T3/T4 and once enough T3/T4 is produced it inhibits the further release of TRH.

Positive feedback is the opposite. In this case, Z would only increase the amount of X released, which would in turn, further increase Z. Thus, positive feedback results in a cycle of amplification and some other means outside of the pathway is required to control the amplification if it is not to be limitless. AN example of this is child birth. When a contraction occurs, oxytocin is released. However, the function of oxytocin produces further contractions, which in turn produces more oxytocin, and so on and so forth.

Answer 3

With negative feedback you have a stimulus which travels to an integration center, such as the brain, and a response that is OPPOSITE the stimulus, the purpose being to bring the situation into homeostasis.  An example would be the thermostat in your house.  The normal temperature might be 70 degrees.  As the house heats the temperature gage in the thermostat is engaged and the air conditioner turn on until the heat goes back down to 70 degrees, then it stops as homeostasis has been reached.  Another example of negative feedback is putting your finger on a hot stove.  The message travels to the brain which sends a message back to the muscles of your hand to remove your finger from the stove.

A positive feedback mechanism takes place when there is a stimulus which upsets the homeostatis of the body.  But instead of acting against it, the body's response is to move TOWARDS it until it is brought to completion.  The best example is childbirth.  Once labor starts, the body continues to labor, increasing until the child is born.