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Unformatted text preview: 1/19/11 IB 132 Today’s Outline Human Physiology Lecture 2: Control theory Professor George A. Brooks Professor Daniela Kaufer •Welcome back! administra=ve points •Feedback control –nega=ve feedback –posi=ve feedback •Feed forward control 1 2 Announcements: Labs (IB 132 L) start next week •Please aNend the sec=on in which you are enrolled –Vacant seats will be ﬁlled automa=cally from wai=ng list (do not aNend if wait listed) –No sec=on changes Email communica=on – we will not be able to answer most ques=ons by mail. Please aNend our oﬃce hours. Bspace site: Study ques=ons, keys, chat room Iclcikers: Points – 5 points for 75% aNendance (starts on the third week, ques=ons are throughout the lecture) Register your iclicker online: hNp://www.iclicker.com/dnn/ What if my clicker id is no longer readable? hNp://www.iclicker.com/registra=on/lookup.aspx If you have never registered your clicker before: Come to my oﬃce hour, to retrieve the number. Sharing iclickers or clicking for friends is strictly prohibited, and will result in failing the course. 3 4 1 1/19/11 Homeostasis • Homeostasis is a dynamic, not a sta=c, process. • Physiological variables can change drama=cally over a 24‐hr. period, but the system is s=ll in overall balance. • When homeostasis is maintained, we refer to physiology; when it is not, we refer to pathophysiology. Homeostasis – at all levels: from molecules to organisms 5 6 Homeostasis of the mind??? Happiness.. Predictd level of happiness one year later 7 8 2 1/19/11 Trackyourhappiness.com measured http://www.ted.com/talks/dan_gilbert_asks_why_are_we_happy.html
9 10 By what mechanism(s) is homeostasis maintained? •Today: General Principles •Throughout the course: Examples in Physiology Mechanisms for Maintaining Homeostasis •In the short term, homeostasis is buﬀered by physical and chemical proper=es of the system. •In the longer term, homeostasis is maintained by a control system. 11 12 3 1/19/11 13 14 CONTROL THEORY Control theory deals with the means by which a system can control or regulate a variable in the face of factors that tend to disturb it. CONTROL SYSTEMS: 1. feedback control The control ac=on is somehow dependent upon the output. Nega=ve feedback control Posi=ve feedback control 2. Feed forward control The control ac=on is independent of output. 15 16 4 1/19/11 Deﬁni=on : Nega=ve Feedback Control System One in which the control ac=on decreases the eﬀect of any disturbance the controller compares the controlled variable (‘what you have’) to the desired value (‘what you want’) and acts to reduce the diﬀerence between the two. Nega=ve feedback holds a variable rela=vely constant in the face of changing condi=ons 17 18 Example: The thermostat in this room –a Nega=ve Feedback Control System that Regulates Room Temperature The actual room temperature is deﬁned to be the output of the control system (‘what you have’) what you have 19 20 5 1/19/11 The controller compares the actual T with the temperature set point (‘what you want’) The controller sends a signal to the heater to lessen any diﬀerence between the set point and the actual room temperature what you want what you have It acts to bring ‘what you have’ closer to ‘what you want’ 21 22 A ‘closed loop’, or ‘feedback’ control system is one in which the control ac=on depends on the output feedback 23 24 6 1/19/11 25 26 Control of body temperature in response to cold exposure [T] : Integra=on of unconscious and conscious (behavior) physiology 27 28 7 1/19/11 NEGATIVE FEEDBACK CONTROL OF [ATP] in the Glycoly=c Pathway Advantages of nega=ve feedback: ‐ Automa=c compensa=on for disturbances ‐ The controller can work even if some components change 29 30 31 32 8 1/19/11 33 34 35 36 9 1/19/11 37 38 Posi=ve feedback examples: ‐ Prolifera=on of cells in development ‐ Voltage dependent Na+ channels in an ac=on poten=al ‐ Childbirth ‐ Sexual arousal ‐ Clinical example: epilep=c seizures 39 40 10 1/19/11 Advantages of posi=ve feedback: ‐ Drives system to extremum ‐ Rapid , automa=c response Feed forward control system Deﬁni=on: One in which the control ac=on is independent of the output 41 42 Feedfroward examples: ‐ an=cipatory control of body temperature ‐ prepara=on for ﬁght or ﬂight response ‐ An=cipatory postural adjustments 43 44 11 1/19/11 ADVANTAGES OF FEEDFORWARD CONTROL •CAN MINIMIZE (EVEN ELIMINATE) EFFECT OF DISTURBANCE •FAST BECAUSE ANTICIPATES EFFECT OF DISTURBANCE COSTS OF FEEDFORWARD CONTROL •NEEDS GOOD PREDICTION (SMART CONTROLLER) •MISTAKES MAY BE COSTLY 45 46 The Main Points •Feedback control: the control ac=on depends on the output •Nega=ve feedback control reduces the eﬀects of disturbances •Posi=ve feedback control drives a system to an extremum •Feedforward control an=cipates the eﬀect of a disturbance 47 48 12 1/19/11 Clinical CorrelaBon • A 64‐year‐old, fair‐skinned man in good overall health spent a very hot, humid summer day gardening in his backyard. Auer several hours in the sun, he began to feel dizzy and confused as he knelt over his vegetable garden. Although he had earlier been perspiring profusely, his swea=ng had eventually stopped. Because he also felt confused and disoriented, he could not recall for how long he had not been perspiring, or even how long it had been since he had taken a drink of water. He called to his wife, who was alarmed to see that his skin had turned a pale blue color. She asked her husband to come indoors, but he fainted as soon as he tried to stand. The wife called for an ambulance, and the man was taken to a hospital and diagnosed with a condi=on called heat stroke. What happened to this man that would explain his condi=on, and how does it relate to homeostasis? 49 13 ...
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