Unformatted text preview: here the computer screen is visible. To start with, we
will collect a practice trace. Relax your jaw, holding a comfortable position with the mouth slightly open.
. Try to hold this relaxed position for at
The non-patient student should click the Collect button
least 5 s. This should give a stable baseline on the trace. If your trace is not a ﬂat line, try again until it is.
Once you have established how to keep a ﬂat line with a relaxed jaw, you are ready to take the EMG
trace. Start the collection. Keep your jaw relaxed for about 5 s, then in the next 5 s open your mouth as
wide as you can and close it a few times. Repeat this 5 s of relaxed jaw and 5 s of opening and closing
until the end of the trace.
We will look at some basic statistics from the EMG trace. The minimum and maximum values, along
with the matching time points, will be given in the statistics box. A more interesting value is the peakto-peak height of the trace. This is simply (maximum potential) − (minimum potential). The statistic box
also gives the mean, which is the arithmetic average of the selected range. The median is the middle value,
if all values were arranged in numerical order.
Select the trace from ∼10-15 s, making sure you have only the relaxed part of the trace. Click the Stats
. A box will appear showing the statistics for these selected range.
Click somewhere in the white part of the graph to clear the selection. The statistics box should have
remained where it was. Select one of the moving portions of the graph and get the statistics for this part
as well. Click and drag both statistic boxes, so that they are not covering up any of EMG trace and both
Copy this EMG trace with the statistics to your worksheet and use the statistics to answer the questions
on the worksheet. 14 Open a new graph in Logger Lite by clicking on
(or with Ctrl+N).
Obtain a piece of chewing gum. While chewing the gum, take a new EMG trace in the same way as
before, relaxing for 5 s, then chewing vigorously for 5 s, and repeating throughout the duration of the
trace. Add statistics for the relaxed portion and for the chewing portion.
Copy the graph to the worksheet. What is the peak-to-peak voltage while chewing gum? Is this more
or less than simply opening and closing the jaw? By what factor?
At the end of the lab, all students should remove the electrodes from their skin. If any sticky residue
remains, use the electrode you just removed to dab against the residue. It should easily remove.
GSIs, please package remaining unused electrodes in the zipper-seal airtight bags and take them
to Dennis’ ofﬁce for storage in the refrigerator. 7 Questions
1. How might the sampling rate change the interval analysis when looking at the EKG traces?
2. If the mean differs greatly from the median in a given data set, what does that indicate about the
 "Willem Einthoven - Nobel Lecture: The String Galvanometer and the Measurement of the Action Currents of the Heart". http://www.nobelprize.org/nobel_prizes/medicine/
 Timothy McKay. Physics for the Life Sciences II. Version 0.7, 2011.
 David Halliday, Robert Resnick, Jearl Walker. Fundamentals of Physics. 6th Edition Extended,
 Vernier EKG Sensor user manual. http://www2.vernier.com/booklets/ekg.pdf
 "Easy EKG for Beginners Including Einthoven’s Triangle Video." http://www.youtube.com/
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