Skeletal Muscle PDF

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Report for skeletal muscle practical (peak contractile force)...

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SKELETAL MUSCLE

BIOL1040

Case Study You are working as a physiotherapist at the Royal Brisbane & Women’s Hospital. One of your patients has recently recovered from an operation which left them bedridden for 2 months; they have suffered chronic muscle atrophy during this time. 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 the stimulus strength (V) applied to theB. marinus scietic nerve will increase force generated by the gastrocnemius muscle (mN).

Prediction of Results for Experiment 1

Predicted peak of contractile force (mN)

12 10 8 6 4 2 0 0.00

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Stimulus Strength (V) Figure 1: Predicted effect of increased stimulus strength (V) on the peak contractile force (mV) 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

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1400.00 1200.00

Peak contractile force (mN)

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Figure 2: The effect of increased stimulus strength (V) on the peak contractile force (mV) inB. marinus gastrocnemius muscle. Each data point is from the mean of three replicates, with the passive force being kept constant at 250 mN.

Comparative Analysis Table 1: A comparative analysis between three separate groups, showing the relationship between the maximum contractile force generated (mN) and minimum stimulus required for near maximum contraction (V) of B. marinus gastrocnemius muscle. Maximum contractile force generated Minimum stimulus required for Muscle Sample (mN) near maximum contraction (V) Your own

1295mN

0.1V

Alternative 1

1710mN

0.5V

Alternative 2

1569mN

0.4V

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EXPERIMENT 2 Hypothesis 2 As the frequency (Hz) between 5 stimuli applied to the nerve of theB. marinus is increased, the final peak contractile force (mN) produced by the gastrocnemius muscle increases.

Materials and Methods 2 A Bufo marinus gastrocnemius muscle was removed prior to the commencement of the experiment and soaked in Frog ringer solution to prevent osmotic imbalance. The leg was then placed into a nerve bath that was connected to a power lab unit, with the force transductor attached to B. marinus by connecting stimulating electrodes to the presynaptic end of the nerve and recording electrodes at the post synaptic end of the nerve. The stimulus applied to the B. marinus was observed and regulated using LabChart 8 software. The force transductor was calibrated so that the output was in milliNewtons (mN) as this is a more meaningful unit of measurement for force, ensuring that the passive force remained at 250mN. To observe the relationship between frequency and peak contractile force, the number of pulses in the Repeats box was set to five, while the stimulus strength remained at 3ooV. The frequency was altered to show results at 1Hz, 2Hz, 3Hz, 4Hz, 6Hz, 8Hz and 10Hz. Results for frequency was tested three times in order to calculate a mean, thus increasing reliability of the results. The negative control of this experiment was the peak contractile force of the gastrocnemius muscle at a frequency of 1Hz, to display how the muscle responds to 5 pulses of force.

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.

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Predicted peak contractile force (mN)

12 10 8

6 4 2 0 0

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Stimulus Frequency (Hz) Figure 3: The predicted effect of stimulus frequency (Hz) on peak contractile force (mN) in a 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.

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1750.00

Peak contractile force (mN)

1700.00 1650.00

1600.00 1550.00 1500.00

1450.00 0.00

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12.00

Stimulus frequency (Hz) Figure 4: The effect of increased frequency (Hz) on the peak contractile force (mV) in B. marinus gastrocnemius muscle. Each data point is from the mean of three replicates, with the passive force being kept constant at 250 mN.

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.

Results from figure 4 show that there was a steady increase in the peak contractile force (mN) produced by the B. marinus gastrocnemius muscle when the frequency (Hz) of 5 pulses was increased. This is evident as the mean peak contractile force produced by the muscle at a minimum frequency of 1Hz was 1515mN, whereas at a max frequency of 10Hz the muscle reached a mean peak contractile force of 1692mN, having an overall average increase of 177mN. However, at a frequency of 2Hz, there is a 38mN decrease in the peak contractile force before rising to 1577mN at a frequency of 3Hz. There is a drastic increase in peak contractile force between 2Hz and 4 Hz, showing an overall increase of 217mN. However, from 4Hz to 10Hz the peak contractile force begins to plateau, generating an average increase of only 28mN at 10Hz. Our data was compared to the data of two other groups, and while values varied slightly they both portrayed the similar trends and relationships to that of our own data.

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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. As shown by the results in figure 2, the hypothesis was confirmed as increasing the stimulus strength (V) applied to the B. marinus sciatic nerve resulted in an increase of the force generated by the gastrocnemius muscle (mN).

2. Discuss the biological processes that explain why peak contractile force changes with different stimulus strengths.

Muscle organs such as the gastrocnemius muscle are comprised of several individual muscle fibres that respond to a stimulus in an all- or-none fashion, meaning that the overall peak contractile force produced by the muscle is dependent on the number of motor units being contracted (Hudson, Lavidis, Choy, Franklin 2005). Because of this, as stimulus strength increases, progressively more muscle fibres reach their thresholds and contract, increasing the force generated by the muscle. 3. What are the biological reasons for the differences in the comparative analysis, and how do these reasons explain the varied outcomes?

Biological factors that may have influenced the variations between data sets is the possibility that each group utilised a gastrocnemius muscle that was derived from three different B. marinus samples. The sex of the B. marinus from which the muscle was obtained from would influence results, as the muscle in male specimens have a larger physiological cross-sectional area due to the higher levels of testosterone. Because of this, larger muscles are able to generate a higher peak contractile force due to a larger number and size of muscle fibres (Urry, Meyers, Cain, et al 2017).

4. Briefly describe (in complete sentences) whether the results of your second experiment confirm or disconfirm your hypothesis. As shown by the results in figure 4, the hypothesis of experiment 2 was confirmed as when the frequency (Hz) between 5 stimuli applied to the nerve of the B. marinus was increased, the final peak contractile force (mN) produced by the gastrocnemius muscle increased.

5. Discuss the biological processes that explain the trends your results illustrate.

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As shown, there was a steady increase in peak contractile force as the stimulus frequency was increased. This is because following an initial stimulus, if a second stimulus is applied before the muscle has relaxed again, it causes a second twitch on top of the first (Urry, Meyers, Cain, et al 2017). Because of this, a greater total force developed- this is referred to as mechanical summation. As the frequency of stimulation is gradually increased, there is less and less time for the muscle fibres to relax between stimuli and tetanus occurs, where eventually the contractions blend into one smooth powerful contraction (Hudson, Lavidis, Choy, Franklin 2005). 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.

Muscular atrophy describes the process of muscle reduction and occurs in two forms- disuse atrophy (where the muscles waste away due to lack of exercise) and neurogenic atrophy (where the muscle deteriorates due to injury or disease (Bonaldo and Sandri 2013).

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.

Muscle organs are made up of several individual muscle fibres that respond to a stimulus in an all- or-none fashion, meaning that the strength of the contraction a muscle produces is dependent on how many muscle fibres are recruited. The stronger the stimulus, the greater the amount of muscle fibres that will respond and produce a contraction (Hudson, Lavidis, Choy, Franklin 2005).

References List any references you have used in your answers, in the panel below .

Hudson, N.J., Lavidis, N.A., Choy, P.T. and Franklin, C.E. (2005). Effect of prolonged inactivity on skeletal motor nerve terminals during aestivation in the burrowing frog, Cyclorana alboguttata. J. Comp. Phys A – Neuroethology, Sensory, Neural and Behavioral Physiology 191(4): 373-379. Urry, L.A., Meyers, N., Cain, M.L., et al (2017) Campbell Biology, 11th Ed, Pearson Education, Australia. Bonaldo, P., Sandri, M. (2013) Cellular and Molecular Mechanisms of Muscle Atrophy, Dis Model Mech. 6(1):25-39

© 2017 The School of Biomedical Science

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