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PhysioEx 8.0 Exercise 2 Skeletal Muscle Physiology Answers
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Single Stimulus
Activity 1:  Identifying the Latent Period

1.   How long is the latent period?    3.33   msec
2.   Does the latent period change with different stimulus voltages? no

Activity 2:  Identifying the Threshold Voltage

1.   What do you see in the Active Force display? Deadline at zero
2.   What is the threshold voltage?  .8    V
3.   How does the graph generated at the threshold voltage differ from the graphs generated at voltages below the threshold? Below threshold they were deadline graphs

Activity 3:  Effect of Increases in Stimulus Intensity

1.   How did the increases in voltage affect the peaks in the tracings? Increases in voltage made the peaks rise
2.   How did the increases in voltage affect the amount of active force generated by the muscle? Active force grew
3.   What is the voltage beyond which there were no further increases in active force? Maximal voltage:         8.5   V
4.   Why is there a maximal voltage?  What has happened to the muscle at this voltage?  Max voltage is like the muscles limits, if there are no limits then there are injuries. It was at the contraction phase
5.   An individual muscle fiber follows the all-or-none principle—it will either contract 100% or not at all.  Does the muscle we are working with exhibit the all-or-none principle?  Why or why not? No, there was no contraction at .5V but there was at 1.0 -10.00. The muscle only contracts if there is enough force active.

Multiple Stimulus
Activity 4:  Treppe

1.   What do you observe? The muscle follows all three phases: latent, contraction, and relaxation when the single stimulus button is clicked

Activity 5:  Summation

1.   What is the active force of the contraction?   1.83    gms
2.   What is the active force now?     2.89    gms
3.   Was there any change in the force generated by the muscle? Yes, force increased
4.   Was there any change in the force generated by the muscle? Yes
5.   Why has the force changed? The muscle never relaxed, so the contraction was stronger
6.   Do you see the same pattern of changes in the force generated? Yes
7.   Does the force generated change with each additional stimulus?  If so, why? Yes, summation is when muscle twitches overlap and cause stronger contractions creating a greater force.

Activity 6:  Tetanus

1.   What begins to happen at around 80 msec? the active force begins to plateau
2.   What is this condition called? Tetanus (unfused)
3.   How does the trace at 130 stimuli/sec compare with the trace at 50 stimuli/sec? Twitches are closer together
4.   What is this condition called? Fused Tetanus
5.   At what stimulus frequency is there no further increase in force? 146
6.   What is this stimulus frequency called? Max titanic tension

Activity 7:  Fatigue

1.   In fatigue, what happens to force production over time? Force production slowly goes down until it reaches zero

Isometric and Isotonic Contractions
Activity 8:  Isometric Contractions

1.   Looking at your graph, what muscle lengths generated the most active force? (provide a range)         70       to       80          mm
2.   At what muscle length does passive force begin to play less of a role in the total force generated by the muscle?      70         mm
3.   Looking at your graph, at what muscle length does passive force begin to play a role in the total force generated by the muscle?     80          mm
4.   The graph shows a dip at muscle length = 90 mm.  Why is this? Most active force is generated at the length of 80mm
5.   What is the key variable in an isometric contraction? When the amount of force of an object is greater than the amount of force that is applied, the muscles isometrically.

Activity 9:  Isotonic Contractions

1.   How much time does it take for the muscle to generate 0.5 grams of force?         Msec 3.77
2.   At what point in the trace does the muscle shorten? Beginning
3.   You can observe from the trace that the muscle is rising in force before it reaches the plateau phase.  Why doesn’t the muscle shorten prior to the plateau phase? Because enough force hasn’t been generated to move the load
4.   Did it take any longer for the muscle to reach the force it needed to move the weight? No
5.   How does this trace differ from the trace you generated with the 0.5 gram weight attached?    More force has to be generate to lift the weight 
6.   Examine the plot data and your numerical data.  At what weight was the velocity of contraction the fastest?     1.0    grams
7.   What happened when you attached the 2.0 gram weight to the muscle and stimulated the muscle? When the muscle reached the peak of the contraction phase, the muscle immediately entered the relaxation phase.  How did this trace differ from the other traces? The muscle did not plateau. What kind of contraction did you observe? Isotonic contraction
8.   What kind of trace did you get? The force started at 0.5 but there was no change
9.   What was the force of the contraction?     0.5    grams
10.   With the 1.0 gram weight, what kind of trace did you get?  started at a force of 1.0, there was no change to the trace. What was the force of the contraction?   Passive 1.00    grams
11.   With the 1.5 gram weight, what kind of trace did you get?  started at a force of 1.5, there was no change to the trace.  What was the force of the contraction?    Passive 1.51   grams
12.   With the 2.0 gram weight, what kind of trace did you get? started at a force of 1.75, there was a slight increase to 1.86 and then the trace leveled back off at 1.75. What was the force of the contraction?     Active 0.11/passive 1.75 for a total of 1.86  grams
13.   Describe your four tracings and explain what has happened in each of them. For the weight of 0.5 the trace started at a force of 0.5, there was no change to the trace.  For the 1.0 trace, the trace started at a force of 1.0, there was no change to the trace.  For the 1.5 trace, the trace started at a force of 1.5, there was no change to the trace.  For the 2.0 trace, the trace started at a force of 1.75, there was a slight increase to 1.86 and then the trace leveled back off at 1.75.
14.   What muscle length(s) generated the fastest contraction velocity? 70 and 80mm

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PhysioEx 8.0 Exercise 2 Skeletal Muscle Physiology Answers
3 years ago
This deserves another read, bump...

Thanks for this.


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