Skeletal Muscle Structure and Function Lab Exercise

Introduction to Skeletal Muscle Structure and Function

Gain an understanding of skeletal muscle structure and function; ? Perform exercises to demonstrate recruitment, tetanus, and fatigue; and ? Practice data collection, summary, and analysis Preparation: ? Carefully read the materials in this Lab 2 Manual. o You have the option of completing the exercises during the Lab 2 session (synchronously) or on your own time (asynchronously). o If you will be completing the exercises during the session, please gather the materials you will need before the session begins. ? View the ‘Deconstruction of an Introduction’ presentation. ? Consider the feedback you were given on your Pre-Lab 2 Assignment. You will have the opportunity to ask questions to your TA during this session. Background Reading: Moyes CD, Schulte PM. 2015. Principles of animal physiology. 3rd Edition. Toronto: Pearson Benjamin Cummings. Chapter 6, Cellular movement and muscles; p. 208 – 255. Laboratory Outline: The laboratory consists of two exercises. In the first exercise, you will demonstrate motor unit recruitment in the “Bag Curl Workout”. You will write about results from the “Bag Curl Workout” for Question 3 of the Lab 2 Assignment. In the second exercise, you will demonstrate muscle fatigue in the “Clothespin Workout”. This experiment will be the basis of your manuscript Introduction in the Pre-Lab 2 and Lab 2 Assignments. And you will prepare a figure of the results from the “Clothespin Workout” for Question 2 of the Lab 2 Assignment. For both exercises, you will record your data using the worksheet found in Appendix 1. After the laboratory you must: Individually complete the Lab 2 Assignment (9.5% of final grade) on Quercus and submit online by the deadline. Nadia Morson and Christopher Garside Fall 2020 2 The assignment includes: 1. A written Introduction section of a scientific manuscript which explores a possible cause of skeletal muscle fatigue, based on the “Clothespin Workout” experiment. o Incorporate the feedback provided to you in your Pre-Lab 2 Assignment. o An appropriate title for a manuscript in which your Introduction would appear. o Your Introduction should include: ? Relevant background information ? Identification of the ‘gap’ in the knowledge in the field ? Rationale for investigating this ‘gap’ ? Presentation of a hypothesis or research question ? A brief explanation of how the experiment will be conducted. This must include how you measured the ‘factor’ responsible for the observed fatigue. Same as your Pre-Lab 2 Assignment (refer to page 3 of the Pre-Lab 2 Assignment). ? A brief mention of the key findings/results (optional) o You should include only three cited (referenced) sources: Pre-Lab 2 Manual, Chapter 6 of Principles of Animal Physiology (3rd Edition) by Moyes and Schulte, and one appropriate peer-reviewed primary research article (selected by you). ? Note that if it appears in the Literature Cited section, it must be cited in-text also. ? For assistance with your citations, please see the file ‘Citing Sources in BIO270H1 and BIO271H1’ in the Lab Assignment Tips and Resources section of the General Online Lab Information Module on Quercus. o To receive full marks, students must address the format and style guidelines in Appendix 1 of the Pre-Lab 2 Assignment. 2. Create a single figure illustrating your “Clothespin Workout” results, comparing the data from your dominant hand and non-dominant hand. 3. Answer a question related to your “Bag Curl Workout” about motor unit recruitment. Electromyography (EMG): The measurement of the electric potentials generated by muscles is called electromyography, and recordings of these potentials is called an electromyogram, or EMG. The action potentials generated by contracting muscle alter the electrical charge in the surrounding extracellular fluid. These electrical changes are conducted through body fluids, and can be detected from the surface of the skin using electrodes applied to the skin. The EMG signal is the recorded consequence of two principal bioelectric activities: Nadia Morson and Christopher Garside Fall 2020 3 1. Propagation of motor nerve impulses and their transmission at the neuromuscular junctions of a motor unit, and 2. Propagation of muscle impulses along the sarcolemma and the T-tubular systems resulting in excitation-contraction coupling. The EMG is not a series of predictable waves like those of the electrocardiogram (ECG), but a burst of spike-like signals. Integrating this complex signal will give an indication of the intensity of muscle activity during a contraction. Although the electrical impulse generated and conducted by each muscle fiber is very weak (less than 100 ?volts: which is close to levels of background noise), many fibers in a motor unit and multiple motor units conducting simultaneously induce voltage differences large enough to be detected by a pair of surface electrodes and visualized after signal integration. Note that each fiber is a different distance from the electrode, and therefore signals take different times to reach the electrode. Therefore, the surface EMG actually provides indirect information about levels of motor unit activity. Furthermore, at any instant in time the electrical potential between different parts of the muscle can be either positive or negative, depending on which end of the muscle fiber is experiencing the action potential. Thus, the voltage recorded can be either positive or negative, and changes rapidly. EMGs can be used diagnostically to detect damage to muscle or to the neural pathways responsible for triggering muscle contractions. Instead of measuring your own EMG data, you will visualize example EMG data collected when performing the same exercises that you will perform. You can find this example EMG data for each exercise on Quercus in the Lab 2 module. Caution: If any discomfort or pain is felt during the exercises, discontinue and consult the TA or instructor. Exercise 1: Motor Unit Recruitment – “Bag Curl Workout” Objectives: ? To demonstrate motor unit recruitment in dominant and non-dominant arms, and visualize example EMG data during this exercise; ? To determine the maximum curling weight for your dominant and non-dominant arms and correlate to differences in size of muscle; and ? To observe, record, and correlate motor unit recruitment with increased force of skeletal muscle contraction. In this exercise, you will demonstrate motor unit recruitment and fatigue through the contraction of your biceps muscle, during a biceps curl, by gradually increasing the load. Nadia Morson and Christopher Garside Fall 2020 4 Setup and Preparation: To complete this exercise, you will need the following materials: o A bag (cloth, plastic, paper, etc.) with handles that are durable enough to lift items of various weights inside the bag ? Examples: a bookbag, reusable shopping bag, or backpack o 5-10 items that can fit inside your bag together ? Examples: books (textbooks, cookbooks, novels, etc. are best), filled water bottles, household items, etc. ? Avoid using electronics to minimize physical damage and water damage if you plan to use water-filled items o Measuring tape ? Alternatives: string/paper/cloth and a ruler o Scale (optional) o A space to safely complete the exercise (seated or standing) Instructions: 1. Gather the required materials to complete the experiment. These materials will need to be easily accessible (within arm’s reach) during the experiment. o You will also need to have the worksheet (Appendix 1) ready to record your data. o Note: Collect the data from this experiment accurately and to the best of your abilities. You will be answering a question about the results of this experiment that will be graded in the Lab 2 Assignment. 2. Before you begin the exercise, use your measuring tape to measure the circumference of your biceps muscle of your dominant arm and non-dominant arm. Record on the worksheet. 3. Beginning from either a seated position or a standing position (Figure 1), you will prepare to complete your first biceps curl. Proper biceps curling technique involves: (i) keeping the elbows pinned to sides, (ii) curling up to shoulders and down to straight arm position, and (iii) curling slowly and with control (Figure 2). In these examples (Figure 1), you will replace the dumbbell with your bag. You will also be curling one arm at a time, not both at the same time. Nadia Morson and Christopher Garside Fall 2020 5 Figure 1: Correct form for biceps curls in a seated or standing position. Photos from Google Images. Figure 2: Proper bicep curling technique. Key features: (i) elbows pinned to sides, (ii) curl slowly and with control, (iii) curl up to shoulders and down to straight arm position. Photo from Google Images. 4. Once you are ready in position, begin with the dominant arm and hold the handle of the bag in your dominant hand. For your first repetition, you will curl the empty bag. Record the difficulty score on the worksheet. Nadia Morson and Christopher Garside Fall 2020 6 o For example, if you write with your right hand, this is your dominant hand and you will begin with your right hand. 5. Fill the bag with more items. Curl. Record. 6. Repeat until you have either (i) filled the bag to the maximum capacity, or (ii) you can no longer curl the bag because it is too heavy (use your judgement and discretion here). o If you have a scale, weigh the filled bag and record on the handout. o Don’t overdo it and strain yourself to curl the filled bag. Again, if at any time you feel uneasy or uncomfortable, discontinue the exercise. 7. Repeat steps 3-7 on your non-dominant arm. 8. View the EMG recordings of Motor Unit Recruitment in the Lab 2 module on Quercus. 9. Answer the remaining questions on the worksheet (Appendix 1) for your dominant arm. Exercise 2: Muscle Fatigue – “Clothespin Workout” Objectives: ? To demonstrate skeletal muscle fatigue in dominant and non-dominant arms, and visualize example EMG data during this exercise; and ? To observe, record, and graph skeletal muscle fatigue. You will demonstrate skeletal muscle fatigue during a pinching exercise. The primary intrinsic muscles responsible for pinching are the adductor pollicis, first dorsal interosseous, and flexor pollicis brevis muscles. Setup and Preparation: To complete this exercise, you will need the following materials: o A clothespin ? Alternatives: any spring-loaded clip (hair clip, binder clip, chip bag clip), or anything you can squeeze between fingers that will reshape when pressure is released ? Additional alternatives: using the opposite motion, you can “open” or expand an elastic band or hair tie o A stopwatch ? You can use the Google stopwatch (by searching ‘stopwatch’ into the Google search bar), or you can use the stopwatch in the Clock app on your smartphone o Someone to help you count repetitions or record on the worksheet (optional) o Measuring tape ? Alternatives: string/paper/cloth and a ruler Nadia Morson and Christopher Garside Fall 2020 7 o A space to safely complete the exercise (seated) Instructions: 1. Gather the required materials to complete the experiment. o You will also need to have the worksheet (Appendix 1) ready to record your data. o Note: Collect the data from this experiment accurately and to the best of your abilities. You will be graphing the results of this experiment and will be graded on it in the Lab 2 Assignment. 2. Before you begin the exercise, measure the circumference of your dominant forearm and non-dominant forearm. Record on the handout. 3. In a seated position, hold the clothespin (or alternative) between your index finger and thumb of your dominant hand (Figure 1). Prepare your stopwatch. Figure 3: Squeezing a clothespin, hair clip or binder clip using the index finger and thumb. Alternatively, using the index finger and thumb to expand an elastic band. Photos from Google Images. 4. For 2 minutes, you will squeeze and release the clothespin, in a pinching motion, as many times as you can without stopping. Using the stopwatch as a timer, Nadia Morson and Christopher Garside Fall 2020 8 record how many times you can pinch the clothespin during every 30 second interval. o Alternatively, you could expand the elastic band using your index finger and thumb and count how many times you can stretch to the maximum range within the 30 second intervals. For example, have the stopwatch running for the duration of the exercise. Keeping an eye on the stopwatch for each 30 second interval, count how many squeezes you complete in each trial and record it on the worksheet. You will complete 4 trials, each lasting 30 seconds. Therefore, you will record 4 values for the number of pinches (or alternative, ex. number of stretches of the elastic). o Important: Do not stop or pause between 30 second trials! To see the greatest effect of the muscle fatigue, you must continue the exercise consistently for the 2 minutes. o If you need to pause to record the value, be as quick as possible before returning to the exercise. 5. Repeat steps 3 and 4 using your non-dominant hand index finger and thumb.