Lecture 1 - Feedback and Nervous System

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Biology/Animal Physiol & Neurosc
BIPN 100
Laurie Smith

9/30/13 Lecture 1   The top is homeostatic.  Even though there is a ripple, the variation of the ripple remains around the same average value (~37).  It is a small variation around a specific value  The bottom is allostatic.  Intially, it varies around 37, then the temperature increases and it varies around 40, not 37.  This is what happens when someone has a fever.  It varies around different values   The component that is at the blunt end affects the component on the arrow end.  In this case, a change in component 1 directly leads to a change in component 2, a change in component 2 does not change anything in component 1.  It doesn’t go backwards, only one way  + sign = a change in the same direction  If component 1 gets smaller, component 2 gets smaller  - sign = a change in the opposite direction  These components are connected in a loop, if there was no connection between 1 & 3, it would be a feed forward not a feedback system   Comparing unit compares output from sensor with a set point.  If they are equal, nothing happens  If the reading of sensor is lower than the set point, the comparing unit will turn on the controlled(furnace) that will increase the air temp  If the temperature of sensor is too high, then nothing happens and furnace shuts off  This is an example of a loop with components  In a fever, the set point changes in the hypothalamus and the system will just regulate around the higher value  COMPONENT A ---(+)----> COMPONENT B ----(+)-----> COMPONENT C -----(-)-----> COMPONENT A  If A gets bigger, B gets bigger, then C gets bigger, then A gets smaller  Component c have negative feedback control towards component A  Negative feedback loops tend to stabilize the control variable  There may be some ripple and variation, but the components of a negative fed back system interact in a way that stabilizes the system  Positive feedback drives a system to its extreme values (death)  If a change in component A gets smaller, B would get smaller, C would get smaller, A would get even smaller, etc.  Positive feedback is uncommon in physiological systems because they drive things to extremes. They do not work with life.  Perturbation: Anything that causes a change in a system  Perturbation can happen anywhere in the loop   I
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