feed back mechanisms (1 Viewer)

[cowsdontmoo]

does any one have info on them cuz i DNT!!!!!!!!!!!!!

 

[Buiboi]

you wanna know what it is? or you want an example?

 

[fernando]

have you read the notes on this site for bio? there should be something about it there.

 

[zingerburger]

Feedback mechanisms all have to do with the maintenance of homeostasis.

Positive feedback is when an increase in something is detected by a receptor and and effector is triggered to lower whatever was increased e.g. skin detects rise is air temperature, sends message to brain (control centre) where hypothalamus triggers sweat glands to activate.

Negative feedback is the opposite of positive, obviously. So if the receptor detects a decrease in something, and effector will activate to increase it e.g. hypothalamus detects lower blood pressure, processes a message to send to adrenal glands, secretion of aldosterone that increases reabsorption of sodium ions, water follows by osomosis and leads to increase in blood pressure. In this case, the hypothalamus acts as both the receptor and control centre.

You may have also modelled a feedback mechanism. Our class did this by heating a bi-metal strip with a bunsen. The strip was held between two nails stuck into a cork. The nails and strip were connected to a circuit in such a way that if the strip touched either of the nails, it would activate a light globe. Our job was to keep that from happening. So in this case, our eyes acted as the receptor (detection of light from globe or change in shape of metal strip), brain acted as control centre (processed information from eyes to send to effector), and the arm acted as the effector (moved the strip away from the bunsen to cool it down and change its shape again). This experiment is hard to explain in words, but I hope you understand what's happening.

So does all that help? As always, your textbook is usually a good point of reference. It may have more information.

 

[Buiboi]

Feedback mechanisms all have to do with the maintenance of homeostasis.

Positive feedback is when an increase in something is detected by a receptor and and effector is triggered to lower whatever was increased e.g. skin detects rise is air temperature, sends message to brain (control centre) where hypothalamus triggers sweat glands to activate.

Negative feedback is the opposite of positive, obviously. So if the receptor detects a decrease in something, and effector will activate to increase it e.g. hypothalamus detects lower blood pressure, processes a message to send to adrenal glands, secretion of aldosterone that increases reabsorption of sodium ions, water follows by osomosis and leads to increase in blood pressure. In this case, the hypothalamus acts as both the receptor and control centre.

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i thought the difference between teh positive and negative feedback was like not based on the fact that ones a decrease and the other an increase, but thefact that negative feedback was more on the idea of counteracting the problem via doing the opposite in order to bring temperature, pressure or whatever it may be back to normal, whereas the positive one was where it encourages the same reaction to occur to bring back to equilibrium.


eg. negative feedback: increase in temperature = thermoreceptors in skin sense the increase/decrease in temperature= receptors send impulses to the control centre, being the brain, specifically the hypothalamus, there it analyses the impuls and initiates a response, which it sends signals to the effectors in the muscle glands which implement the counteracting response ... such as shivering to keep warm

positive, btw, is the rare one, not many on this one : a pregnant woman who is experiencing pain and erratic levels in the internal environment cuased by the muscle contractions, and basically it they're encouraged to keep up with these muscle contractions to give birth and return to normal

im not sure on the difference between the psoitive and negative, i marked it off as one im uncertain about. But yerah i could be wrong on this, if so tell me so and tell me the difference!

 

[zingerburger]

Whoops. Yeah, from doing a bit of extra reading I think you're absolutely right, Buiboi.

 

[Buiboi]

lol yeah im still confused ...:mad1:

 

[xiao1985]

for negative feed back, the body essentially is trying to get back to an "optinum" level... so if the level is too high, the body will lower it; if the level is too lower, the body will raise it

for positive feed back, there ain't an "optinum" or "equilibrium" as such.... ie, increased level will further cause more increase in the level.

 

[Buiboi]

so then wats the point of positive feedback if it doesnt bring any levels back to normal?

 

[xiao1985]

If a system is EVER at positive feed back, then my guess is that, there is no normal level to begin with.

 

[kloudsurfer]

so then wats the point of positive feedback if it doesnt bring any levels back to normal?

The point of negative feedback is to decrease the effects of the stimulus (bringing it back to the normal level and thus maintaining homeostasis)

The purpose of positive feedback is to increase the effects of the stimulus. It is not supposed to return it to normal levels, but is supposed kind of build up on the effect of the stimulus. I cant think of any good examples atm...

 

[jannny]

A positive feedback example would be fire surrounded by heaps of wood. It builds up and increases the effect of its stimulus, but never goes back to its normal levels. (unless the wood runs out etc.)

 

[xiao1985]

A positive feedback example would be fire surrounded by heaps of wood. It builds up and increases the effect of its stimulus, but never goes back to its normal levels. (unless the wood runs out etc.)

Good example... though not in a biological context though =p

 

[Buiboi]

ok how bout my example i gave b4
pregnancy in women
the idea of muscle contractions....now can you finish it off?

 

[Buiboi]

A positive feedback example would be fire surrounded by heaps of wood. It builds up and increases the effect of its stimulus, but never goes back to its normal levels. (unless the wood runs out etc.)

but if it never returns to its normal or optimal or however you wanna classify it as, then how is the positive feedback mechanism of benefit? like the feedback mechs are under the dot point where you gotta consider how it consists of the detection and counteracting stages....how do these 2 stages relate to the positive feedback if there is no optimal level as xiao said b4 and thus no counteract? and like the fire eg, if the fire doesnt stop then there is no counteracting mech? what the shit! im confused i dun get this positive mech

 

[xiao1985]

i'm not entirely sure about the pregnant woman analogy. I would more inclined to describe a "feed back mechanism" to be something body initiated. Not something human can control. (i.e. negative feed back cannot really be "controlled" by human)

The example I learnt was the transmission of information in neurological network, IIRC. The entrance of Na+ and K+ into the membrane (?) promotes further entrance of Na+ and K+ down the neuron to enter the membrane due to the potential difference established. Hence the pulse of message is "sent" around the body.

 

[kloudsurfer]

The pregnant woman thing is right (kinda).

I think what he is talking about is this hormone (the name escapes me at the moment) that is released to relax the walls of the birthing tract thingy (as you can see, im a bit sketchy on it!). This allows the baby to pass through. The pressure from the babys head as it passes through stimulates the production of more of this hormone, which in turn relaxes the muscles even more....and so on...

Like I said, Im a bit sketchy on it allso this probably makes no sense lol. The fire example is better...

 

[xiao1985]

Apologies then, I am short on knowledge on this example =/

 

[kloudsurfer]

Apologies then, I am short on knowledge on this example =/

No probs, so am I lol.

Just remembered, the hormone is oxytocin.

 

[budj]

Hey,

Yep for pregnancy your riht about oxytocin. Also the transmission of an action potential is positive feedback as well.

You could also quote any example where a hormone acts on a cell inducing a increase in receptor expression (cant think of the top of my head).

Negative feedback: hypothalamus induced control is always awesome to talk about, just remember that the context of this point is in "Mainaining a balance" so when you discuss this always have "homeostasis, or homeodynamics" in the background and logic of your explanation.