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answers to exercise 2 physio 9.0
EXERCISE 2: Skeletal Muscle Physiology
Student Name:
ACTIVITY 1: The Muscle Twitch and the Latent Period Answers
1. The latent period of the skeletal muscle that was tested in this lab simulation was
a. about 1 second.
b. less than 1 msec.
c. between 2-3 msec.
d. variable, depending on the voltage that was applied to it. C.2-3 msec
2. True or False: Another name for a muscle cell is “myofibril.” False
3. The largest active force that could be generated in the muscle is Activity 1 was _______ grams. 1.82
4. Define the terms skeletal muscle fiber, motor unit, skeletal muscle twitch, electrical stimulus, and latent period. Skeletal muscle fiber- muscle composed of striated muscle that are elongated. There are thousands of cells that cause the muscle to be tense
Motor unit- all muscle cells, approximately 1,500 muscle fibers of the skeletal muscle that is controlled by one motor neuron
Skeletal muscle twitch- mechanical response to a single electrical stimulus
Electrical stimulus- electrical pulses set for precise voltage, frequency, and duration, acetylcholine triggers actions
Latent period- time that lapses between generation of action and start of muscle contraction, no force generated during this time, and no chemical changes i
5. What is the role of acetylcholine (ACh) in a skeletal muscle contraction? This is the chemical signal the nerve sends to the skeletal muscle to cause contraction. This comes from the end-plate and the contraction starts.
6. Describe the process of excitation-contraction coupling in skeletal muscle fibers. This process converts electrical stimulus to a mechanical response stimulus. The stimulus is the action and the contraction is the mechanical response. The action releases ACH and restructures the ions to create depolarization of the end-plate. This is the cause of the excitation-contraction.
7. Describe the three phases of a skeletal muscle twitch. A muscle twitch is a single contraction. The three phases are:
Latent- no activity of muscle contraction
Contraction- muscle tension high and the highest amount of force involved
Relaxation- occurs after contraction and ends when the muscle contraction has stopped
8. Does the duration of the latent period change with different stimulus voltages? No the latent did not change through all experiments. This was the answer I chose.
9. At the threshold stimulus, do sodium ions start to move into or out of the cell to bring about the membrane depolarization? This is the influx (move in) of sodium ions to cause the membrane depolarization.
ACTIVITY 2: The Effect of Stimulus Voltage on Skeletal Muscle Contraction
10. The threshold voltage for the muscle in this lab simulation was ________ volts. When that voltage was used to stimulate the muscle, ________ grams of active force were generated. 0.8Volts
0.02 grams-Active force
11. True or False: In a resting skeletal muscle cell, most of the calcium ions freely move through the cytoplasm of the cell. False
12. Describe the effect of increasing stimulus voltage on isolated skeletal muscle. Specifically, what happened to the muscle force generated with stronger electrical stimulations and why did this change occur? Muscle force generated increased as the electrical stimulation became stronger. When more voltage is increased the fibers activate for total increase of force in the muscle.
13. How is this change in whole-muscle force achieved in vivo (eg. in the human body)? The amount of the electrical current determines the amount of force. The current has to go past the threshold to create increased muscle force. With higher voltage and increased force will meet the maximum for tension. This process is reached in vivo with more motor units to increase the muscle force.
14. What happened in the isolated skeletal muscle when the maximal voltage was applied? Fibers become depolarized and create an active force with maximum voltage.
ACTIVITY 3: The Effect of Stimulus Frequency on Skeletal Muscle Contraction
15. True or False: There is no limit to the amount of force that a skeletal muscle can generate if it is stimulated by a high enough voltage at a very high frequency. False
16. The chemical ion or molecule that is primarily responsible for initiating the contraction of a muscle fiber is
a. Na+
b. K+
c. Ca2+
d. ADP C. Ca2+
17. What is the difference between stimulus intensity and stimulus frequency? Stimulus intensity- is the amount of intensity of a stimulus to produce a response from the sensory system
Stimulus frequency- the number of times per unit times the stimulus is presented
18. In this experiment you observed the effect of stimulating the isolated skeletal muscle multiple times in a short period with complete relaxation between the stimuli. Describe the force of contraction with each subsequent stimulus. Is this called treppe or wave summation? This is called treppe. Stimulating the skeletal muscle numerous times for short periods, with relaxation periods in between, the stimulus increased force. This reached a maximum peak to see where the force happened.
19. How did the frequency of stimulation affect the amount of force generated by the isolated skeletal muscle when the frequency of stimulation was increased such that the muscle twitches did not fully relax between subsequent stimuli? Is this called treppe or wave summation? This is wave summation. Stimulation frequency was increased with no muscle relaxation, and the force increased with each stimulus. A muscle twitch if overlapped will bring no relaxation. Stimulus occurs continuously for a short time, and contraction is higher.
20. To achieve an active force of 5.2 g, did you have to increase the stimulus voltage above 8.5 volts? If not, how did you achieve an active force of 5.2 g? To get the active force of 5.2g stimulus was delivered in short time, rapid succession, and no relaxation. There was no increase to 8.5g.
ACTIVITY 4: Tetanus in Isolated Skeletal Muscle
21. When stimuli were applied to the muscle frequently enough to cause a plateau in the amount of force generated, a state known as ____________ ____________ occurs. Unfused Tetanus
22. Why do children (and adults) receive an immunization (actually several!) called a “tetanus shot”?
a. This will prevent the development of muscle fatigue when she/he becomes an athlete.
b. The person will then be able to develop the maximum amount of force from each and every muscle in her/his body.
c. To prevent the development of a condition called “lockjaw” that can develop from a specific bacterial infection.
d. This will a reminder to her/him to keep the skin washed and clean when she/he is outside playing. C. to prevent development of condition…
23. The maximal tetanic tension of the muscle in this simulation was _________ grams. 5.95
24. Describe how increasing the stimulus frequency affected the force developed by the isolated whole skeletal muscle in this activity. Frequencies:
50s/s- force at lowest level
130s/s- slight increase of force
146-150s/s- force reached peak and maximum tetanic tension
25. Indicate what type of force was developed by the isolated skeletal muscle in this activity at the following stimulus frequencies: at 50 stimuli/second, at 140 stimuli/second, and above 146 stimuli/second. 50- Unfused Tetanus
140- Fused Tetanus
146+- Maximal Tetanus Tension
26. Beyond what stimulus frequency is there no further increase in the peak force? What is the muscle tension called at this frequency? Maximal Tetanic Tension
ACTIVITY 5: Fatigue in Isolated Skeletal Muscle
27. True or False: The primary reason for muscle fatigue is the buildup of Ca2+ ions in the muscle fiber. False
28. If an intervening rest period is imposed on active muscle,
a. it will then be able to generate much more force.
b. the development of fatigue will be delayed.
c. muscle hypertrophy can be prevented.
d. muscle atrophy can be prevented. B. development of fatigue delayed
29. When a skeletal muscle fatigues, what happens to the contractile force over time? The contractile declines due to previous activity. No increase in force by the muscle because of the maximum tetanic tension. Once there is fatigue the contractile decreases over time.
30. What are some proposed causes of skeletal muscle fatigue? 1. ADP
2. Decrease of calcium levels
3. Pi in muscle fibers
4. Lactic acid buildup
31. Turing the stimulator off allows a small measure of muscle recovery. Thus, the muscle will produce more force for a longer time period if the stimulator is briefly turned off than if the stimuli were allowed to continue without interruption. Explain why this might occur. A rest period occurs and intercellular concentrations are decreased. The concentrations being decreased and any length of time the muscle can reach maximum tension. Simulator kept on gives no rest time and continuous fatigue.
32. List a few ways that humans could delay the onset of fatigue when they are vigorously using their skeletal muscles.
ACTIVITY 6: The Skeletal Muscle Length-Tension Relationship
33. In a force-length graph,
a. the muscle length is the independent variable.
b. the amount of force generated is the dependent variable.
c. both active and passive forces must be considered.
d. All the above are correct. D. All
34. According to your lab manual, the protein titin is the primary cause of _________ __________. Passive force
35. In this lab simulation, the muscle length of _______ mm was able to generate the largest active force. 1.82
36. The force that results from muscles being stretched is called
a. active force.
b. passive force.
c. maximal tetanic force.
d. stretch force. B. Passive force
37. What happens to the amount of total force that the muscle generates during the stimulated twitch? Prediction : change either way
Muscle lengthened- passive force increases
Muscle Shortened- active force increases
38. Based on the unique arrangement of myosin and actin in skeletal muscle sarcomeres, explain why active force varies with changes in the muscle’s resting length. During shortened rest active force increases, muscle shortened.
During longer rest active force decreases and muscle lengthens.
The cause of change for the active force is amount of myosis attached to actin,
39. What range of skeletal muscle lengths generated passive force? 80, 90, 100
40. If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically? The muscles are contracting with no lengthening. Isometrically would be anytime the biceps are at a certain length for a certain time.
ACTIVITY 7: Isotonic Contractions and the Load-Velocity Relationship
41. The fastest muscle contraction velocity measured in this part of the simulation occurred with the ______ weight.
a. 2.0 gm
b. 1.5 gm
c. 1.0 gm
d. 0.5 gm D. 0.5 gm
42. The fastest muscle contraction velocity in this simulation was approximately ________ mm/msec. 0.100 mm/msec.
43. True or False: A muscle that is contracting isometrically will fatigue much slower than one that is contracting isotonically. True
44. If you were using your biceps muscles to curl a 7kg dumbbell, when would your muscles be contracting isotonically? The arm extends down and to a point of being straight or the goes from down to being raised up,
45. Explain why the latent period became longer as the load became heavier in the experiment. The muscle has a rise in tension, no movement, no contraction,. Cross bridges cycle and muscle tension is cause from overloading. The muscle generates necessary force.
46. Explain why the shortening velocity became slower as the load became heavier in this experiment. Shortening velocity- speed of contraction of muscles shorting while lifting a load.
Light load- shortening velocity at maximal
Heavy load- decreases to slower velocity
47. Explain why it would take you longer to perform 10 repetitions lifting a 10kg weight than it would to perform the same number of repetitions with a 5kg weight. Weight of load increases
Latent time increases
Shortening velocity increases
Smaller weight muscle contracts faster in latent and shortened velocity speeds.
48. Describe what would happen in the following experiment: A 2.5g weight is attached to the end of the isolated whole skeletal muscle used in these experiments. Simultaneously, the muscle is maximally stimulated by 8.5 volts and the platform supporting the weight is removed.
a. Will the muscle generate force?
b. Will the muscle change length?
c. What is the name for this type of contraction? 1. Force is from stretching muscle and caused by recoil of the tissue.
2. If platform is removed and weight is still connected. The length change would be from muscle contraction.
3. Isometric
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