Question and answers related to the first seven lectures:

Recitations and Labs # 01, # 02, #3 06 The goal of this recitations / labs is to review material for the first test of this course. Info on osmosis, diffusion, metaboism, transport across biological membranes, communication and muscle, has been referred to in lectures and is presented in labs as computer simulations related to homeostasis, signal transduction, endocrine and neural communication, and muscle function. Although no additional info is presented in the lab section, its content allows for a better discussion of the material presented in the lecture / recitation course. Question and answers related to the first seven lectures: Ranking of most important items for recitation / lab #1 An active learning technique to study physiology Ranking of most important items for recitation / lab #2 A recitation question with a structure and function of your choosing Ranking of most important items for recitation / lab #3 A recitation question involving neuroendocrine components A Model of Active Learning Probably a single most important tip for the course is to prepare SENTENCES with what you consider are the main punch lines for each lecture. You should RANK them in what you consider is a list from most to less important ideas given in each lecture. You should EDIT them, as for example, checking if more than one sentence might be combined into a better sentence. Finally, make sure that your sentences cover the whole of the topic presented in each lecture. Use this list to discuss material with fellow students and with your instructor." Please be aware that in order to write a single, concise and informative sentence you need to UNDERSTAND, rather than memorize, a piece of information. To test yourself on how good you are doing this, check if your sentence used your own words or if you are just borrowing part of a sentence you read in your textbook. Consider that if you can not write an idea into a single and simple sentence, you probably have not yet understood the material.! When you are editing your notes, either from lectures or from your textbook, it is important to have a PLAN that tells you where are you going with your editing. A good suggestion for this plan is to develop a set of QUESTIONS that you think each lecture was attempting to answer. List all possible questions, then edit and rank the questions, and finally answer them by merging your lecture notes and the notes you might have summarized from your textbook.! The PARAGRAPHS in the following slides are an example of notes you might have taken from a lecture or from a textbook. Use these notes as an exercise by turning them into sentences, then editing them, and finally by ranking them. Make sure you merge your notes from lectures with your notes from your textbook and make sure your ranked sentences cover the whole material presented in lectures. This is your recitation and Lab #01.! 1

Recitation question and Lab # 01 If you can not write an idea into a single sentence,! you probably have not yet understood the material. Recitation question and Lab # 01 Example of questions Example of an answer based on the pre-requisite material Example of statements for one of these question What is life? What is physiology? How is life mantained? What is structure - function? What is energy, where does it comes from, how is it used and how is it controlled? Energy is the capability to do work. Energy originates from the sun, it is stored in chemical bonds of macromolecules and it is readily available from cellular ATP. Use of physiological sources of potential energy is regulated by enzymatic control of intermediary metabolism (nt & hormones). Specific cells, tissues, organs & organisms have evolved biological structures in order to optimized the use of energy for specific functions (e.g. muscle vs mucosa cell). A main source of potential energy is the ionic difference across plasma membranes. 2

Recitation question and Lab # 01 Example of questions Example of an answer based on the pre-requisite material Example of a statement for all of these question What is life? What is physiology? How is life mantained? What is structure - function? What is energy, where does it comes from, how is it used and how is it controlled? Life, whose only purpose is to keep being alive, is based on enzyme - driven chemical reactions, in compartamentalized environments. Recitation question and Lab # 01 The main punch-line for this question is that there is not a single best answer, but just the one you understood the better. Better answers will be correlated with a better understanding of the background information on which the topic material is based. The next slide has a list of questions students should ask themselves when attempting to understand physiological issues (the circle), as those required to answer the weekly questions. 3

The circle as a way of thinking What is the goal for the system or lecture topic you are now studying?! Which are its main structures and its main functions?! Which are its main structure - function relationships, at the different organizational levels?! Which are its main control elements, at the different organizational levels?! Which are its main inputs, integrators, outputs, and feedback elements?! Which are its main links or relationship with other systems or lecture related topics?! Which are its main homeostatic failures or clinical pathologies?! Questions to be asked of any homeostatic system" Questions to be asked of any homeostatic system ( the circle )" 4

Recitation questions # 02 & # 03 Sept 11" If you can not write an idea into a single sentence,! you probably have not yet understood the material. Recitation questions # 02 & # 03 If you can not write an idea into a single sentence,! you probably have not yet understood the material. 5

Recitation questions # 02 & # 03 a) structure Which, increase or decrease? function b) c) d) How do you know? Parts to total? Two feedbacks and an absolute requirement? The circle as a way of thinking An excellent way to pick-up structure and functions to answer recitation questions is study classic experiments / approaches, as those in the lab computer simulations course (1-credit).!! Lab simulations not only focus your thoughts on specific and important aspects of material presented in lectures, but also provide summaries, experiments, and tests that will help you review the lecture / recitation and lab courses material.!! Finally, lab periods not only allow further discussion of each recitation answers for the lecture / recitation course as well as any lecture topic in doubt, but they also provide you with extra time for answering all your tests, since they use two adjacent periods on Wednesdays, when all tests are scheduled.! If you can not write an idea into a single sentence,! you probably have not yet understood the material. 6

Virtual Lab # 02 The goal of this virtual lab session is to review pre-requisite material for the integrative physiology course. This info has been referred to in lectures and is presented here in computer simulations related to osmosis, diffusion, metabolism, & transport across biological membranes. 06 Physiology Interactive Lab Simulation (PhILS) Students should review all simulated experimental labs available in the software package used for this course. Students should perform the different labs following the instructions and time schedule defined for each lab. Physiology Interactive Lab Simulations (PhILS version 2.0 has fewer labs than PhILS version 3.0) Frog heart function 18 thermal and chemical effects 19 refractory period of the heart 20 Starling s law of the heart 21 heart block ECG and heart function 22 ECG and exercise 23 the meaning of heart sounds 24 ECG and finger pulse 25 electrical axis of the heart 26 ECG and heart block 27 abnormal ECG Circulation Blood 28 cooling and peripheral blood flow 29 blood pressure and gravity 30 blood pressure and body position 31 ph and Hb - O2 binding 32 DPG and Hb - O2 binding Respiration Digestion 33 altering body position 34 altering airway volume 35 exercise - induced changes 36 deep breathing and cardiac function 37 Glucose transport 7

PhILS - Osmosis and Diffusion (varying ECF concentration) 1) Use a virtual pipette to dispense a blood sample into a tube 2) Use a virtual spectrophotometer to measure color of blood 3) Show that RBCs take up water and burst in dilute NaCl solution 4) Show that water leaves RBC and it shrives in high NaCl solution 5) Relate concentration of incubating solution to RBC integrity 6) Report the range of NaCl solutions isotonic to RBC PhILS - Osmosis and Diffusion (varying ECF concentration) Most cell membranes have very few open Na channels, so when they are placed in solutions of NaCl, very few Na ions move across the membrane. If the fluid inside the cell has a different concentration from NaCl solution outside, water will move across the membrane. If the NaCl solution is isotonic, there will be not net flux of water across the membrane and cell integrity will be maintained. Physiological saline is a 0.9% solution of NaCl or about 155 mm. This lab shows that the integrity of sheep blood is maintained in this solution. 8

PhILS - (size and basal metabolic rate) 1) Perform least square linear regression and fit data to the formula y=mx + b to calculate the rate of oxygen consumption 2) Examine the effect of the weight on the metabolic rate of animals of different sizes 3) Demonstrate that the rate of O2 consumption is directly proportional to the weight of the animal 4) Demonstrate that the rate of O2 consumption by a cell is indirectly proportional to the weight of an animal PhILS - (size and basal metabolic rate) Smaller animals have fewer cells and consume less O2 than larger animals. However, not all cells have the same metabolic rate, and this lab shows that the cell from a smaller animal consume more O2. Rubner explained this observation in terms of surface area to volume ratios and showed that one square inch of surface area (skin) from a small animal is served by fewer cells. If cells generate enough heat to maintain body temperature and compensate for the heat lost across the skin, clearly the fewer cells in smaller animals must work harder and consume more O2, than cells in larger animals. 9

PhILS - (cyanide and electron transfer) 1) Use a virtual pipette to dispense a blood sample into a tube 2) Use a virtual spectrophotometer to measure color of solutions 3) Perform least square linear regression and fit data to the formula y = mx + b to calculete the rate of color change 4) Show that cyanide interferes with the electron transport sytem PhILS - (cyanide and electron transfer) Cyanide poison the electron transport system and blocks ATP production in the mitochondria. This concepts was demonstrated in this experiment by using a dye that competed with the electron transport system for electrons but was not poisoned by cyanide. The rate of dye color changed increased in the presence of cyanide because the breakdown of succinic acid made more electrons available to the dye: no electrons went to the poisoned transport system. 10

PhILS - Digestion (glucose transport) Frog heart function 18 thermal and chemical effects 19 refractory period of the heart 20 Starling s law of the heart 21 heart block ECG and heart function 22 ECG and exercise 23 the meaning of heart sounds 24 ECG and finger pulse 25 electrical axis of the heart 26 ECG and heart block 27 abnormal ECG 1) Describe the steps involved in exposing and isolating a length of small intestine from a small mammal 2) Use a virtual pipette to dispense solutions into a tube 3) Use a virtual spectrophotometer to measure a solution color 4) Explain the role of the Na / K ATPase pump in the transport of glucose across the wall of the small intestine. Circulation 28 cooling and peripheral blood flow 29 blood pressure and gravity 30 blood pressure and body position Blood 31 ph and Hb - O2 binding 32 DPG and Hb - O2 binding Respiration 33 altering body position 34 altering airway volume 35 exercise - induced changes 36 deep breathing and cardiac function Digestion 37 Glucose transport PhILS - Digestion (glucose transport) Frog heart function 18 thermal and chemical effects 19 refractory period of the heart 20 Starling s law of the heart 21 heart block ECG and heart function 22 ECG and exercise 23 the meaning of heart sounds 24 ECG and finger pulse 25 electrical axis of the heart 26 ECG and heart block 27 abnormal ECG Circulation 28 cooling and peripheral blood flow 29 blood pressure and gravity 30 blood pressure and body position Blood 31 ph and Hb - O2 binding 32 DPG and Hb - O2 binding Respiration 33 altering body position 34 altering airway volume 35 exercise - induced changes 36 deep breathing and cardiac function Digestion 37 Glucose transport The Na / K ATPase pump and Na / glucose transporter molecules are required for glucose transportation across the wall of the small intestine. The pump is located in the baso-lateral membranes of the absorptive cells and creates a creates a low concentration of Na inside the cell. A co-transporter molecule allows Na to enter down this concentration gradient from the lumen of the gut. Glucose is transported into the cell with Na and then out of the cell by facilitated diffusion through the baso-lateral membrane, into the intertitial fluid. This exercise demonstrated the uptake of glucose across the gut wall and also showed that ouabain, a Na / KATPase pump poison, halts glucose uptake. 11

Virtual Lab # 03 The goal of this virtual lab session is to review material for the integrative physiology course. This info has been referred to in lectures and is presented here in computer simulations related to endocrine communication, neuronal communication, and muscle function. 06 Physiology Interactive Lab Simulation (PhILS) Students should review all simulated experimental labs available in the software package used for this course. Students should perform the different labs following the instructions and time schedule defined for each lab. Physiology Interactive Lab Simulations (PhILS version 2.0 has fewer labs than PhILS version 3.0) Frog heart function 18 thermal and chemical effects 19 refractory period of the heart 20 Starling s law of the heart 21 heart block ECG and heart function 22 ECG and exercise 23 the meaning of heart sounds 24 ECG and finger pulse 25 electrical axis of the heart 26 ECG and heart block 27 abnormal ECG Circulation Blood 28 cooling and peripheral blood flow 29 blood pressure and gravity 30 blood pressure and body position 31 ph and Hb - O2 binding 32 DPG and Hb - O2 binding Respiration Digestion 33 altering body position 34 altering airway volume 35 exercise - induced changes 36 deep breathing and cardiac function 37 Glucose transport 12

PhILS - Skeletal Muscle (resting potential and external K) 1) Describe the steps involved in dissecting tha fast extensor muscle in the cryfish tail 2) Use a virtual instruments to record and measure potentials from muscle fibers 3) Recognize that increasing the level of K in the Ringer solution bathing the muscle depolarize the muscle 4) Employ least square linear regression to illustrate the semi-log relationship between ECF-K concentration and membrane potential. PhILS - Skeletal Muscle (resting potential and external K) The level of K is much higher inside than outside the cell. The ECF-K in cryfish Ringer is 5 Eq/L, and the membrane potential recorded in this lab is around -65 mv. Increasing the concentration of K in the Ringer solution depolarized the cell so that a concentration of 20 meq/l gave membrane potential values or around -50 mv. If the threshold for action potential production is 15 mv about resting level, changing the ECF-K level from 5 to 20 meq/l will depolarize the membrane above threshold and will induce spontaneous muscle contraction. 13

PhILS - Skeletal Muscle (resting potential and external Na) 1) Describe the steps involved in dissecting tha fast extensor muscle in the cryfish tail 2) Use a virtual instruments to record and measure potentials from muscle fibers 3) Recognize that increasing the level of Na in the Ringer solution bathing the muscle depolarize the muscle 4) Employ least square linear regression to illustrate the semi-log relationship between ECF-Na concentration and membrane potential. PhILS - Skeletal Muscle (resting potential and external Na) The level of Na is much higher in the ECF than in the ICF. This means that the membrane potential and the concentration gradient both draw Na into the cell. This simulation shows that decreasing the concentration gradient by decreasing Na outside the cell hyperpolarize the cell membrane. However, a 10-fold change in the Na level produces a change in membrane potential by only 8 mv. This small effect in membrane potential indicates that small fluctuations in ECF-Na have a minimal effect on the membrane potential of the cells in the body. 14

PhILS - Action Potentials (the compound action potential) 1) Describe steps involved in dissecting sciatic nerve from a frog 2) Connect electrodes at different locations along the nerve 3) Use a virtual Data Acquisition Unit to apply electrical shocks and display evoked compound action potentials (CAPs) as a line tracing on the screen 4) Show threshold by rising the shock voltage and evoking a CAP 5) Show recruitment by relating shock voltage to CAP amplitude 6) Measure the CAP amplitude and illustrate data graphically and by superimposing the tracing on the screen PhILS - Action Potentials (the compound action potential) In this lab a mild shock brought a few axons to threshold and elicited a small CAP. Increasing shock voltage recruited more axons into the response until all axons in the sciatic nerve were above threshold and produced an action potential (AP). It is significant that the CAP is produced by an AP in a population of axons with the same conduction velocity. Imagine if these were motor axons supplying fibers in the same muscle. AP produced simultaneously in several motor neurons would travel down the axons at the same speed and arrive at the neuromuscular junction at the same time. Clearly this characteristic allows the CNS to control the timing of muscle fiber activation and contraction. 15

PhILS - Action Potentials (conduction velocity and temperature) 1) Describe steps involved in dissecting sciatic nerve from a frog 2) Connect electrodes at different locations along the nerve 3) Use a virtual Data Acquisition Unit to apply electrical shocks and display evoked compound action potentials (CAPs) as a line tracing on the screen 4) Measure the time difference between CAPs conducted along different lengths of nerve and calculate the velocity of AP conduction along axons in the sciatic nerve. 5) Describe the effect of cooling on AP conduction velocity. PhILS - Action Potentials (conduction velocity and temperature) The sciatic nerve contains populations of axons that conduct AP at similar conduction velocities. This lab studied a population of axons that conduct AP at a velocity of around 30 m/s at room temperature. Cooling the nerve to 10 C slowed the conduction velocity to about 20 m/sec. This observation is explained in terms of the effect of cooling on the function of proteins, like enzymes and channels. Decreasing the t C slows the rate of channel opening and closing thereby increasing the duration of the AP and slowing the speed of the conduction along the axon. 16

PhILS - Action Potentials (refractory period) 1) Describe steps involved in dissecting sciatic nerve from a frog 2) Connect electrodes at different locations along the nerve 3) Use a virtual Data Acquisition Unit to apply pairs of electrical shocks and display 2 CAPs) as a line tracing on the screen 4) Measure the amplitude of the 2 CAPs and demonstrate how amplitude of the second CAP changes with time. Use the data to determine the relative refractory period. 5) Explain the decline in the amplitude of the second CAP in terms of smaller AP and sub-threshold stimulation of axons. PhILS - Action Potentials (refractory period) An AP is followed by a brief refractory period. During the absolute refractory period the voltage-gated Na channels are inactivated, and in the closed state membrane depolarization does not open these channels so an AP can not be produced. During the relative refractory period, many voltage-gated K channels are open. As a result, the threshold for CAP production is increased and the amplitude of any evoked CAP is reduced. In this lab, the second CAP was smaller during the relative refractory period because some axons were not firing (the shock was sub-threshold) and those that fired produced a smaller CAP. 17

PhILS - Action Potentials (measuring ion currents) 1) Describe the theory underlying the use of voltage clamp with a squid giant axon 2) Use a virtual DAT and voltage clamp to record ion currents when the axon membrane is clamped to a given voltage 3) Perfuse tetrodotoxin (TTX) onto the preparation to block membrane voltage-gated Na channels and observe voltagegated K current. 4) Perfuse tetraethylammonium (TEA) onto the preparation to block membrane voltage-gated K channels and observe the voltagegated Na current. TEA TTX PhILS - Action Potentials (measuring ion currents) control TEA control TTX 18

PhILS - Action Potentials (measuring ion currents) Depolarization of the axon membrane to a level above threshold for action potential (AP) production opens voltage-gated Na channels and voltage-gated K channels. TTX blocks voltage-gated Na channels and abolishes the early inward current. TEA blocks voltage-gated K channels and abolishes the late outward current. These observations show that the action potential is produced by a sequential opening and closing of Na and K channels, and demonstrates that the two ions travel across the membrane through their own channels. PhILS - Synaptic Potential (facilitation and depression) 1) Describe steps involved in dissecting the extensor muscle in the cryfish tail 2) Use virtual instruments to record and measure potentials from muscle fibers 3) Apply pairs of shocks to a nerve to produce two APs in a motor nerve and two EPSP in the muscle fiber 4) Measure the amplitude of the two EPSPs 5) Show relationship between the amplitudes of the two EPSPs 6) Explain the data in terms of the release of synaptic vesicles 19

PhILS - Synaptic Potential (facilitation and depression) PhILS - Synaptic Potential (facilitation and depression) When pairs of EPSPs are produced in quick successions there is an inverse relationship between the amplitudes of the two responses. During facilitation the second EPSP is larger than the first and this can be explained by a slow removal of Ca from the terminal. The second action potential enters the terminal while Ca remains from the first, with the result that the Ca concentration is higher, so more vesicles are released and a a larger (second) EPSP is recorded. During depression, the first action potential releases a huge number of synaptic vesicles and creates a larger EPSP. There are fewer vesicles available for release of the second response so that the second EPSP is small. 20

PhILS - Synaptic Potential (temporal summation of EPSPs) 1) Describe steps involved in dissecting the extensor muscle in the cryfish tail 2) Use virtual instruments to record and measure potentials from muscle fibers 3) Apply pairs of shocks to a motor axon to produce two EPSPs in the muscle fiber 4) Change time interval between the shocks and measure the effect on the amount of muscle membrane depolarization 5) Explain how decreasing the time interval increases temporal summation and increases membrane depolarization PhILS - Synaptic Potential (temporal summation of EPSPs) 21

PhILS - Synaptic Potential (temporal summation of EPSPs) The time course of the action potential is usually shorter than the EPSP it evokes in the postsynaptic cell. A high frequency dicsharge of action potentials could produce EPSPs such that the membrane potential would not return to resting levels between responses. Thus EPSPs could piggy back on one another, creating a phenomenon called temporal summation. In this lab, temporal summation was recorded at a response interval less than 140 ms and the total amount of membrane depolarization created by the two EPSPs was greater than that produced by a single response. A pair of EPSP at an interval of 40 ms depolarized the membrane above threshold for action potential production. PhILS - Synaptic Potential (spatial summation of EPSPs) 1) Describe steps involved in dissecting the extensor muscle in the cryfish tail 2) Use virtual instruments to record and measure potentials from muscle fibers 3) Apply pairs of shocks to a nerve to produce an AP in a motor axon and an EPSPs in the muscle fiber 4) Increase shock voltage to stimulate additional motor axons and increase EPSP amplitude 5) Measure the amplitude of EPSPs and demonstrate that sufficient membrane depolarization will evoke an AP 22

PhILS - Synaptic Potential (spatial summation of EPSPs) PhILS - Synaptic Potential (spatial summation of EPSPs) In many chemical synapses, single EPSPs depolarize the membrane to a level that is sub-threshold for an action potential production. One strategy to produce spikes in such a situation is a phenomenon called spatial summation. EPSPs are created by several synaptic neurons at the same time, so that the EPSPs add together and bring the membrane potential above threshold. In this lab, brief electrical shocks were applied to a nerve containing four motor axons. Activation of an axon to a muscle fiber was seen when an EPSP either appeared or increased in amplitude. Synchronous activity in several motor axons was necessary to produce an action potential in the muscle fibers. 23

PhILS - Endocrine Function (thyroid gland and metabolic rate) 1) Perform least square linear regression and fit data to the formula y = mx + b to calculate the rate of O2 consumption 2) Explain how cooling affects the rate of O2 consumption of mice with a normal and with dysfunctional thyroid gland 3) Explain why the rate of O2 consumption increases in the cold PhILS - Endocrine Function (thyroid gland and metabolic rate) Stress increases the metabolic rate of most cells in the body by increasing the level of thyroid hormones (T3-T4) in the blood. This lab examines the effect of cooling on the rate of O2 consumption of female white mice, on a normal diet and on a diet containing propylthiouracil (PTU), an additive that reversibly abolish thyroid function. Cooling increases metabolic rate but at a certain temperature the metabolic rate increases at a much faster rate as the animals begin to shiver. Animals on the PTU diet shiver at a much warmer temperature presumably because diminished thyroid function is insufficient to generate heat to maintain body temperature. 24

PhILS - Skeletal Muscle (stimulus dependent force generation) 1) Describe steps involved in exposing a frog calf muscle 2) Apply electrical shocks directly to exposed muscle and correlate its contraction with a deflection of a line tracing 3) Demonstrate threshold by increasing the shock voltage and observing the appearance of a muscle contraction 4) Illustrate recruitment by correlating shock voltage with contraction amplitude 5) Measure amplitude of each line tracing deflection and show data graphically by overlying line tracing on the screen PhILS - Skeletal Muscle (stimulus dependent force generation) An action potential in a motor neuron produces an AP in and a contraction of the muscle fibers it supplies. Motor neurons can be activated by Aps in upper motor neurons whose axons run down descending tracts in the spinal cord. Selective activation of motor neurons allows the brain to control the number of active motor neuron units, and thereby control the amount of muscle contraction. 25

PhILS - Skeletal Muscle (length / tension curves) 1) Describe steps involved in exposing a frog calf muscle 2) Use virtual instruments to apply electrical shocks directly to the exposed muscle and display the amount of tension produced by a contraction, as a line tracing on the screen 3) Measure the amount of tension produced by a muscle held at different lengths 4) Demonstrate the relationship between resting length and the amount of tension created by a single contraction 5) Illustrate the relationship graphically and by superimposing successive line tracings 6) Explain the data in terms of cross-bridge number at different sarcomers lengths PhILS - Skeletal Muscle (length / tension curves) The amount of tension produced by a contraction depends upon the muscle length. If the muscle is too short, the thin filament overlap one another and the thick filaments become compressed. At this short length few cross-bridges can be made so little tension is produced. At resting length there is optimum overlap between thick and thin filaments so a maximum of cross-bridges can be formed and a maximum of tension can be achieved. As the muscle is further lengthened, the amount of overlap decreases and the number of cross-bridges and tension declines. 26

PhILS - Skeletal Muscle (summation / tetanus) 1) Describe steps involved in exposing a frog calf muscle 2) Use virtual instruments to apply electrical shocks directly to the exposed muscle and display evoked contraction, as a deflection of a line tracing on the screen 3) Measure the amount of tension produced by a muscle held at different lengths 4) Change the shock frequency and relate changes in the line tracing to summation, incomplete and complete tetanus 5) Determine the time taken for the sarcoplasmic reticulum to take up calcium after a contraction PhILS - Skeletal Muscle (summation / tetanus) The frequency of muscle stimulation affects the evoked movement. Low-frequency stimulation, produces single-twitches as seen when your eyes twitch. Increasing stimulus frequency elicit summation where the muscle fails to relax between contractions, and then tetanus, where prolonged elevated Ca in cytoplasm increases muscle tension. During normal limb movement, motor neurons produce AP at a sufficiently high frequency to elicit complete tetanus. This evokes a smooth contraction, not the shaking effect elicited by incomplete tetanus. Under this conditions force produced by muscle is controlled by changing number and type of contracting muscle fibers. 27

PhILS - Skeletal Muscle (EMG and twitch amplitude) 1) Demonstrate that patch electrodes placed on the skin can be used to record electrical activity from contracting muscles 2) Use virtual recording instruments to display the pressure produced by a volunteer making a fist and the electrical recording (EMG) produced by the contracting muscles 3) Correlate the amount of tension produced by a single muscle contraction of different intensities with the amplitude of the EMG signalson the screen 4) Relate the data to the recruitment of different number of muscle fibers in the contraction response PhILS - Skeletal Muscle (EMG and twitch amplitude) An AP in a motor neuron produces an AP in and a contraction in the muscle fibers it supplies. Motor neurons can be activated by AP in upper motor neurons, whose axons run down descending tracts in the spinal cord. Selective activation of motor neurons allows the brain to control the number of active motor units, and thereby control the amout of muscle contraction. This concept was illustrated in this lab as the amplitude of the electromyogram (EMG), which indicates the number of muscle fibers contracting, was correlated with amounts of tension produced by the muscle. 28