F19 5C Lab 7 Manual

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Physics 5C Lab 7 Manual: EMG & ECG Body Circuits Spring 2019, UCLA Department of Physics and Astronomy Consult Pre-lab materials for additional information and physics background Activity 1: EMG from Finger Motion: Put one sticker on your wrist (similar to its location for the EKG measurements), and another other one on your forearm on the same side. Connect the red alligator clips to these electrodes. Then, put a sticker on your other forearm and connect the black alligator clip. Explore the relationships between different finger muscle movements and the associated electrophysiology signal within the body. Note: the black lead, in general is a reference electrode that should be placed in a location that is not affiliated with the relevant physiological activity being measured and in a location that will not move at all during the recording. Use your best judgment as to where to put your lead, given the wire length limits. Both the positive electrode and the negative electrode have red cables, but the negative electrode has black electrical tape on the end, so you can tell the difference. Review your pre- lab to see how in the electronics of the EKG and EMG, there is a difference amplifier that takes two potential measurements and subtracts the negative electrode value from the positive electrode value. Figure 1 .Example of EMG lead setup. Note the positions of the red leads and the black lead. Activity 2 EKG (ECG): Put a lead sticker on the inside of each wrist as shown in the figure below as well as a third sticker on the back of your left hand. Attach the red alligator clips to the stickers on your wrists, and the black alligator clip to the sticker on the back of your hand. Follow the procedure above to obtain a recording with the SpikeRecorder software. Review your pre-lab for the physics theory behind why you are able to measure this signal. 1

Physics 5C Lab 7 Manual: EMG & ECG Body Circuits Spring 2019, UCLA Department of Physics and Astronomy Consult Pre-lab materials for additional information and physics background Figure 2 : ( left ): Example of EKG lead I setup, where negative electrode is on right arm and positive electrode is on left arm. ( right ): For 5CL Lab 7, red leads are on the inside of the wrist, instead of the arm. The black lead should be on the right (or left) arm instead of the right leg. Determine the negative electrode from the positive by the presence of black electrical tape on the wires. Note: Medical EKG’s are able to see subtle features of the heart’s dipole by comparing potential differences between many pairs of leads. You will be able to see particular aspects of the EKG using the Lead 1 setup with your wrists as the two points. The exact shape of your EKG may look different, and this will be explored in the lab worksheet. Feel free to elaborate more on this in your lab worksheet if you notice that your results are different than expected. However, you are responsible for taking as accurate measurements as possible with the protocol recommended in this manual, which means keeping very still when you are taking your recording. Motion will interfere with your data signal. Activity 3: External muscle stimulation: In this activity, you or a labmate will see the relationship between electricity and muscle contraction from a different perspective using a muscle stimulator device. Take two of the circular electrodes (white with a metal piece in the center), and put them on your forearm in the same way that you put the electrodes for your arm EMG. When you or someone in your group is ready to try, find the LA or TA who has the device - you may need to wait a little while for them to get to you, as the device is shared with the whole class. If nobody in your group is comfortable using the device, you can observe someone from another group doing this activity. Once the TA/LA has brought the device to your table, connect the leads of the stimulator to the two electrodes on your arm. From there, the TA or LA will be operating the device. Let them know when they should turn it on, and they will gradually start to turn up the strength until it causes a noticeable muscle contraction. If you want them to stop turning it up or to turn the stimulator off at any point, please let them know! While doing this activity or watching someone else do it, think about the relationship between the effects of the stimulator and the EMG recordings you did earlier in the lab. Background Information: In Lab 1, you learned about the electrocardiogram (EKG or ECG). Now, with your understanding of electrical circuits, you can appreciate that raw voltage vs. time signal of an EKG allows for determination of the heart rate, along with more subtle details about functionality 2

Physics 5C Lab 7 Manual: EMG & ECG Body Circuits Spring 2019, UCLA Department of Physics and Astronomy Consult Pre-lab materials for additional information and physics background of heart valves and tissue during the heartbeat. Figure 1 shows an EKG signal that has been smoothed to show essential features. You may have seen an EKG raw signal at the hospital, or in a movie scene, where a person’s vital signs are displayed. For more information, visit the Wikipedia page: https://en.wikipedia.org/wiki/Electrocardiography. Figure 1 .Example of experimentally measured Voltage vs. time ECG Signal in 5CL Lab 1 and 7 setup. Note: this signal may look different `than the standard ECG signal because leads might be switched and voltage measurements are taken from the wrists and not the chest. Similar to how an EKG provides the information about electrical activity in your heart, an electromyogram (EMG) provides information about the electrical activity of your muscles. It does this by measuring the potential difference between two points along the muscle, giving insight into how the membrane potential is changing along its length over time. In this lab, you will be recording EKG signals in the same way as you did in lab 1. However, this time, with the physics knowledge you have gained over the course of this quarter, you will be further exploring what the signals represent about the electrical activity in your body. You will also be using EMG recordings to explore how your body signals to muscles to result in voluntary movement. Figure 2. Components of ECG Setup: board controller (left) is connected to computer via USB cable and has an input cable that separates into three measurement leads (right). Figure 2 shows the hardware that you will use to take your measurements. The three leads will make contact with your body via disposable sticker pads that have a flap where the leads can clip on without needing to directly touch your skin. Figure 3 shows where to attach the disposable stickers to obtain a functional EKG reading. Specifically, the black lead sticker goes on the back of a hand, and each of the two red lead stickers go on the inside of the wrist. One sticker goes on each wrist. 3

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Physics 5C Lab 7 Manual: EMG & ECG Body Circuits Spring 2019, UCLA Department of Physics and Astronomy Consult Pre-lab materials for additional information and physics background Figure 3 . (Left) EKG Measurement Lead Setup. (Right) Eye EMG setup. Specific Procedure for operating EKG/EMG Spike Recorder Software and Collecting Data: 1. Once the EKG/EMG is USB connected to the computer (blue cable connected to white computer cable), open the Spike Recorder Software (make window full screen). 2. If program says “No input Device”, click on the gear icon on top left corner of screen and select “Heart and Brain SpikerShield” as the input. 3. You should see your voltage vs. time signal moving in a green line across the screen. 4. Note the time axis scale bar on the screen. To change the time scale bar, scroll the wheel on the computer mouse. 5. Note that the y-axis does not have units, but you can zoom in and zoom out in amplitude by clicking on the plus and minus buttons on the left side of the screen. 6. The signal is displayed in real time, but is not saved until you hit the record button. 7. When you are satisfied with the type of activity signal that the program is showing you (with the time axis and the amplitude zoomed-in as you would like), click the red target record button on the top right side of the screen. Recording will start and a red stopwatch will display the recording time. Record for at least 30 seconds, or analysis will not work with this open source software. Press the red record button again to end the recording, and write down your recording time for later reference. The program saves the file as a .wav file in a “BYB” folder within the documents folder of the computer. You do not have to open this file in the computer windows explorer. Instead, to review and analyze the EKG file that you have saved, click the button that looks like three sets of horizontal lines on the top right part of the screen (directly to the right of the record button). Now you are in a “review” mode, where you can scroll through and see the signal that you have recorded. Additional Analysis can be done by clicking the “chemistry beaker” button on the top left side of the screen (to the right of the USB route button). This opens up a spike recorder option that identifies local maxima or minima in the signal depending on where you click and drag the upper and lower bounds for detection. The program automatically counts all the spikes within the upper and lower bounds during the entire recording. This feature may be used for a more precise heart rate analysis. Lab Objectives and Supplemental Materials: ● Apply electric potential ideas to measuring electrophysiology changes in the human body 4

Physics 5C Lab 7 Manual: EMG & ECG Body Circuits Spring 2019, UCLA Department of Physics and Astronomy Consult Pre-lab materials for additional information and physics background ● Set up the experiment/methods to be able to measure heart activity and different types of muscle activity. ● Create EKG and EMG circuits in the body using electrodes and the external voltage source ● Identifying human behavioral events that connect to particular electrophysiological events ● Compare the ECG and EMG signals, depending on involuntary vs. voluntary muscle contractions. ● Design and conduct an experiment exploring eye muscle electrical activity in the body Background Information and Experiment Motivation: In 5CL lab 7 [Body Circuits], you will apply information from lab 3 [Electrostatics] and lab 4 [intro to circuits] to connect potential measurement readings to electrical changes in the body. These electrical changes in the body are responsible for the action potentials that create and sustain heart contractions and muscle flexions. It is standard practice in biophysics and neuroscience to measure internal voltage changes in the body through fixed voltage probes that detect changes in the body’s voltage as a function of time. Depending on where the voltage probes are placed, the electrical activity relevant body physiology can be connected to specific human behavior and/or life activity. See the figure below for a schematic on the parts to a heart’s contraction and the associated electrical activity created in the body. Figure S3. Physiological relationship between heart contraction and V(t) signal Using the same equipment and software as from lab 1, you will apply your understanding of what it means to take a “voltage measurement” by placing your two leads on particular locations of the body. Recall in lab 3 how you physically measured the potential difference between different locations on the conducting paper in the case of the various charge configurations of the point charge, parallel plate capacitor, and the dipole. In lab 7, the electrical activity inside the body between the two electrodes is most like the dipole configuration, where action potentials of neurons and muscle cells create a separation of charge that creates electric field lines that we can model as a dipole in this lab. The difference between Lab 3 and Lab 7 is that now, the dipole is changing in time. We are not going to go into detail about exactly how the dipole is changing in time. Rather, we will say that when there is a dipole effect from the action potential propagation, the charged, separated ions dissolved in the water of the body are able to 5

Physics 5C Lab 7 Manual: EMG & ECG Body Circuits Spring 2019, UCLA Department of Physics and Astronomy Consult Pre-lab materials for additional information and physics background act as moving charge particles that create a current. Depending on the direction of the net current (direction of positive ion flow), one location of voltage reading on the surface of the skin will have a different value than a voltage reading in a different location. Assuming the resistance of the material remains constant, the larger the current flow, the larger the potential difference between the two points. [There is no part of the body that has no resistance, so you can apply your knowledge of circuits with ∆V = IR]. See the figure below for a schematic on how to think of heart muscle contractions as creating dipole electric field lines in the body. Figure S2. Background regarding how heart cells create macroscope dipole electric field in the body that can be detected via EKG voltage measurement. Note that (b) shows the same equipotential lines that you drew for the dipole in lab 3 (Electrostatics Lab). Where are the charges on the heart located? 6

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