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Unraveling EMG Waveform Mysteries: An Analytical Essay

1. Unlike the discrete waveform from an electrocardiogram, the electromyogram waveform is irregular. Why do you suppose this is? (2)

2. In your own words, explain how the EMG trace changed when you added weights to your arm? Based on the data you collected what can you infer is happening to the muscles as weight is added? (2)

3. In your own words what is coactivation? What are some explanations you can come up with for this phenomenon? (2)

4. Coactivation of abdominal muscle and muscles supporting the spine has been shown to be essential for the bipedal posture of humans. Based on your data, is the coactivation of the triceps necessary for proper functioning of the biceps and vice versa? (2)

5. List the physiological events that occur between delivery of the stimulus and the start of the recorded response (i.e. during the latent period). (9)

6. Which of the contributions to the latent period (that you listed in question 1 above) depends on the position of the stimulating electrode? (2)

7. Based on your results and calculations for nerve conduction velocity, how long would it take for a nerve impulse to travel from the spinal cord to the big toe? Assume that the distance traveled is one meter.

8. Was there variability in the nerve conduction velocity amongst members of your group? What are some explanations for this? (2)


1. In cardiac muscles, all the muscle fibers are in perfect synchronisation. As a result, in echocardiogram we notice a discreet waveform. But in case of electromyogram, it is a recording of unsynchronised activity of many muscle fibers. Also, since this is a recording of a voluntary muscle fiber, the pattern is affected by the relaxation or tension of the subject (Shin, Kambara, Yoshimura, Kang & Koike, 2014).

2. When weight was added to the arm, EMG trace increased as more weight was applied on it and therefore more work had to be done. When the first weight was introduced, the biceps contracted as ATP started to be released to support the weight. As the weight was increased, a similar activity was noticed at a lesser intensity.

3. Co-activation can be defined as a phenomenon in which a muscle activity, such as contraction leads to some minor activity in the antagonistic muscle. This phenomenon occurs to aid joint stability and to coordinate movement even though the muscles are moving in opposite direction (Loveless, 2012).

4. As these muscles support each other, it is necessary to have co-activation between them. To allow maximum flexibility and movement, co-activation is an essential feature of the muscular system (ColÏn, 2015). Opposing forces allows proper movement and flexibility to the body.

5.  At first the axon terminal of the motor neuron receives a nerve impulse, stimulating the release of ACh (Acetylcholine). The diffusion of ACh occurs throughout the synaptic cleft, and binds itself to the receptors which are present in the motor end plates, triggering AP. Followed by Acetylcholinesterase in synaptic cleft destroying Ach so that another AP doesn't come up unless more Acetylcholine is released. The Muscle AP travelling along T tubule opens and calcium ion is released in the sarcoplasmic reticulum membrane, allowing Ca2+ to flow into sarcoplasm. Ca2+ then, on a thin filament, binds with troponin, which then exposes the myosin binding sites (Alexander, 2014). ATP is used by the contraction and actin binds with the myosin heads, swivel then a thin filament is released which gets pulled towards sarcomere centre. Channels are released by Ca2+ and sarcoplasmic reticulum closes and ATP is used by the Ca2+ active pumps to restore low levels of Ca2+ in sarcoplasm. After that in order to block the myosin binding site, the complex of Troponin-tropomyosin slides back into a specific position. The muscle then finally relaxes, and gets ready for the next nerve impulse.

6. The distance of the CNS from the stimulating electrode defines the delay for the message that has to be delivered. This message is required to go through the CNS from the PNS. The muscle fibre connects the electrode(s), which creates a reaction when a message cycle is completed. Therefore conduction of the impulse will be the contributing factor (Beal, Marcoux & Choi, 2012).

7. The conduction velocities based on results and calculations is obtained to be nearly 50m/s. Therefore for a signal to cross a distance of 1m, it would take about 2 milliseconds time (0.02 s).

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