Skeletal Muscle Report

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Biology

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Jun 1, 2024

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Case Study As a physiotherapist at the Royal Brisbane and Women’s hospital, you are treating a patient with chronic muscle atrophy, suffered as a result of being bedridden for 2 months following an operation. A vital aspect of your role in the patient’s recovery is to improve their coordination and muscle strength, and explain how this can be achieved to the patient. EXPERIMENT 1 Hypothesis Increasing stimulus strength (V) will increase the peak contractile force (mV) generated by the gastrocnemius muscle of the B. Marinus. Prediction of Results for Experiment 1 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Stimulus Strength (V) Predicted peak of contractile force (mN) Figure 1: Predicted effect of increased stimulus strength (V) on the peak contractile force (mN) in B. marinus gastrocnemius muscle. Plots represent theoretical data if hypothesis is confirmed ( red ) and if the response is unaffected ( blue ). Results for Experiment 1 1 SKELETAL MUSCLE

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.00 200.00 400.00 600.00 800.00 1000.00 1200.00 1400.00 Stimulus strength (V) Peak Contractile Force (mN) Figure 2: The effect of stimulus strength (V) on the peak contractile force (mN) on the gastrocnemius muscle of the B. Marinus. Comparative Analysis Table 1: Shows the maximum contractile force generated (mN), as well as the minimum stimulus required for a near maximum contraction (V), as well as results from two other groups. Muscle Sample Maximum contractile force generated (mN) Minimum stimulus required for near maximum contraction (V) Your own 1324.4 0.10 Alternative 1 953.99 0.05 Alternative 2 755 0.10 EXPERIMENT 2 Hypothesis 2 An increase in stimulus frequency (V) applied to the nerve will lead to a greater peak contractile force (mV) generated by the gastrocnemius muscle in the B. marinus . 2

Materials and Methods 2 The experiment conducted utilised a gastrocnemius muscle extracted from the leg of a cane toad ( B. Marinus) which was placed across pins of a nerve bath and connected to a power lab using stimulating electrons and recording electrodes. A pin in the gastrocnemius muscle was placed into the bath and connected to a force transductor via a string. Using LabChart, the pulses were set at 5, passive force at 250mN and stimulus strength 0.1V. These values were maintained throughout the entire experiment. Furthermore, the controlled value of this experiment was 1Hz as this allows for the muscle to contract and relax fully while obtaining results. The independent variable was stimulus frequency, with the values being 1-10Hz, 15Hz, 20Hz and 25Hz, and the dependant variable was the peak contractile force of the muscle. At each stimulus frequency, the process was repeated 3 times to obtain sufficient results. Prediction of Results for Experiment 2 N.B. you will need to adjust the x axis range to display the values of your predicted independent variables. Double-click on the x axis to view the formatting axis options, and enter the necessary maximum range value in the “Bounds” field of the Axis options. 0 5 10 15 20 25 0 1000 2000 3000 4000 5000 6000 Stimulus Frequency (Hz) Peak Contractile Force (mN) Figure 3: Predicted effect of increased stimulus frequency (Hz) on the peak contractile force (mN) in B. Marinus gastrocnemius muscle. Plots represent theoretical data if hypothesis is confirmed (red) and if the response is unaffected (blue). Results for Experiment 2 N.B. you will need to adjust the x axis range to display the values of your predicted independent variables. Double-click on the x axis to view the formatting axis options, and enter the necessary maximum range value in the “Bounds” field of the Axis options. 3

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0.00 5.00 10.00 15.00 20.00 25.00 30.00 0.00 500.00 1000.00 1500.00 2000.00 2500.00 Stimulus Frequency (Hz) Peak Contractile Force (mN) Figure 4: The effect of stimulus frequency (Hz) on peak contractile force (mN) of the gastrocnemius muscle of B. Marinus. The data displays the results for the average peak contractile force (mN) across 3 repetitions. Description of Findings for Experiment 2 Write a paragraph of text in the box below, describing the important trends and relationships for all data presented from Experiment 2. The data above displays an upward trend in peak contractile force (mN) as the stimulus frequency (Hz) of the gastrocnemius muscle was increased. A variation in peak contractile force can be observed when the frequency was increased to 1Hz. The results range from 929mN in repetition one, then decrease to 915mN in repetition two and finally increase to 942mN in the third repetition, producing a mean result of 928.67mN. At a stimulus frequency of 2Hz, the results vary again, starting at 950, increasing to 985 and then decreasing back to 965, producing a mean result of 966.67. All other stimulus frequencies showed slight variation among the three repetitions, with the means for each being 1008.67 for 3Hz, 1179.33 at 4Hz, 1309 at 5Hz, 1436 at 6Hz, 1572.33 at 7Hz, 1699 at 8Hz, 1794.67 at 9Hz, 1858.67 at 10Hz, 1951 at 15Hz, 1989 at 20Hz and 1992.67 at 25Hz. Hence the trend displayed by the results shows a slow increase in peak contractile force through frequencies 1, 2 and 3Hz, followed by a sharp gradual increase from 4 to 10Hz, and then a plateau throughout frequencies 15, 20 and 25Hz. This plateau indicates that 1992mN is approximately the maximum contractile force that the gastrocnemius muscle of the B. Marinus can produce. 4

Discussion Remember to treat these questions like short answer questions in the final exam: be specific, clear and concise. 1. Briefly describe (in complete sentences) whether the results of your first experiment confirm or disconfirm your hypothesis. The results from the experiment demonstrate that by increasing the stimulus strength applied to the nerve did increase the peak contractile force of the gastrocnemius muscle however the trend was not linear. Figure 2 demonstrates that when the stimulus is placed at a low concentration of 0.10V the peak contractile force reached 1240mN. When the muscle was placed under 0.20V the peak contractile. Force peaked at 1324mN. The trend showed a slight decrease at 0.25V, 0.30V, 0.40V. However, after 0.40 the peak contractile force started to plateau. 2. Discuss the biological processes that explain why peak contractile force changes with different stimulus strengths. The strength of the stimulus that is applied to the muscle fibre can affect the number of sarcomeres that are activated and the rate in which they contract. Therefore, when a low voltage stimulus is applied to the muscle, only a small number of sarcomeres contract at a slower rate leading to a lower peak contractile force. On the other hand, when a high voltage of stimulus is applied to the muscle more sarcomeres are activated contracting at a faster rate creating a greater peak contractile force. This process is known as summation (Brian R Macintosh, 2006). 3. What are the biological reasons for the differences in the comparative analysis, and how do these reasons explain the varied outcomes? Table 1 represents the values collected from three different groups all in which conducting the same experiment. Although all groups conducted the same experiment the maximum contractile force generated by the gastrocnemius muscles were all significantly different (G1= 1324.4mN, G2= 953.99mN, G3=755mN). This could be due to several factors such as the muscles size, the age of the B. marinus . Because the older B. marinus becomes may be able to produce a higher maximum force creating a larger contractile force than a younger B. marinus . The same can be said about the difference in the group's results for the minimum stimulus required for near maximum contraction. 4. Briefly describe (in complete sentences) whether the results of your second experiment confirm or disconfirm your hypothesis. The second experiment hypothesised that, increasing the stimulus frequency applied to the nerve will lead to a greater peak contractile force generated by the gastrocnemius muscle. Figure 4 confirms this hypothesis as it demonstrates an upward trend in peak contractile force (mN) as the stimulus frequency (Hz) of the gastrocnemius muscle was increased. 5. Discuss the biological processes that explain the trends your results illustrate. Mechanical summation is a process in which a muscle fibre produces a greater amount of force by receiving multiple stimuli in rapid succession. When a muscle fibre is stimulated by a nerve pulse it contracts producing a force. However, the force produced by a single stimulus is limited as the muscle fibre has a refraction period where force cannot be produced without contraction. Therefore, by receiving multiple stimuli in quick succession the muscle doesn’t relax fusing the contractions into a smooth and more powerful contraction leading to a greater summation of force (Ian C. Smith, 2020). 5

6. In the case study, you are working on muscle atrophy. Discuss what happens in atrophy and how muscle mass can increase upon recovery from atrophy, and how under these conditions, contractile force generated for a given stimulus would be affected. Muscle atrophy is the wasting away or loss of muscle due to a lack of protein synthesis or an increase in protein breakdown and can be caused by disuse of muscles or neurogenetic conditions (Cleveland Clinic , 2022). To increase the reduction of muscle mass and recover from muscular atrophy it is necessary to increase protein synthesis by reducing protein breakdown. Resistance training causes mechanical stress on the muscle fibres stimulating protein synthesis and muscle growth (Better Health , 2022). As muscle mass increases the force generated for a given stimulus also increases. This is because muscle force is proportional to muscle cross section area which increases with muscle growth. Therefore, the larger the muscle the more force generated for a given stimulus in comparison to a small muscle (R. J. Maughan, 2010). 6

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7. The patient you are treating does not have a strong science background; explain to them (using complete sentences) how stimulation of skeletal muscle can result in different strength contractions using language which they can understand. The strength of skeletal muscle can be dependent on a variety of different factors including frequency and intensity of the muscle’s stimulation. When a muscle fibre is stimulated by a single action potential it produces a brief twitch contraction. However, when multiple action potentials are produced in rapid succession the muscle fibre produces a sustained contraction known as tetanus. The strength of these tetanic contractions increases with an increase in the frequency of the stimulation creating a much bigger force produced from the muscle. References List any references you have used in your answers, in the panel below . Better Health . (2022, July 11). Resistance training – health benefits . Retrieved from Better Health : https://www.betterhealth.vic.gov.au/health/healthyliving/resistance-training- health-benefits# Brian R Macintosh, D. J. (2006, June 27). Prediction of summation in incompletely fused tetanic contractions of rat muscle . Retrieved from National Library of Medicine : https://pubmed.ncbi.nlm.nih.gov/16806237/ Cleveland Clinic . (2022, January 21). Muscle Atrophy . Retrieved from Cleveland Clinic : https://my.clevelandclinic.org/health/diseases/22310-muscle-atrophy#:~:text=Muscle %20atrophy%20is%20the%20wasting,and%20tingling%20in%20your%20limbs. Ian C. Smith, H. A. (2020, Febuary 13 ). A brief contraction has complex effects on summation of twitch pairs in human adductor pollicis . Retrieved from Eperimental Physiology : https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/EP088401#:~:text=When %20multiple%20electrical%20stimuli%20are,twitch%20force%20and%20twitch %20duration. R. J. Maughan, J. S. (2010). Muscle strength and cross-sectional area in man: a comparison of strength-trained and untrained subjects. British Journal of Sport Medicine , 149-157. © 2017 The School of Biomedical Science 7

Skeletal Muscle Report

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