Lab 2 - Skeletal Muscle Physiology (P. 17)

Introduction:
In this lab, I will study how muscles contract, what makes muscles contract, different types of muscle contraction, and learn about how resistance affects muscle contraction. I will define Key Terms that describe what will occur in the experiments; I will conduct an experiment for each Activity and provide all resulting Data as well as answer Questions from each Activity. I will then provide a short Summary for what I learned in each Activity.

Key Terms:
Recruitment (or Multiple Motor Unit Summation) (p. 18) - greater number of motor units are present in a muscle and are able to be simultaneously stimulated causing an increase in muscle force
Latent Period (p. 18) - The interval between stimulus and response.
Isometric Contraction (or Fixed Length Contraction) (p. 20, 23 in Lab Manual; p. 963 - Hole's) - A contraction in which muscle tension is increased, but the muscle is not.
Treppe (or Staircase Effect) (p. 20) - The occurrence of a successive increases in the extent of contractions following rapid, repeated stimulation of a muscle. Wave Summation (p. 21) - The combination of responses from a motor unit that has had two or more stimuli applied to it in quick succession.
Tetanus (p. 21) - A state of continuous muscular contraction, especially when induced artificially by rapidly repeated stimuli.
Muscle Fatigue (p . 23) - Muscle fatigue is the repeated, intense use of muscles which leads to a decline in performance.Though the actual mechanism for muscle fatigue appears to involve the leakage of calcium.
Passive Force (p. 23) - Any movement produced by a force that is external to the muscle or muscle group normally responsible for the movement.
Active Force (p. 23) - A force due to movement entirely controlled by muscular activity.
Total Force (p. 23) - The process by which multiple or repeated stimuli can produce a response in a nerve, muscle, or other part that one stimulus alone cannot produce.
Isotonic Contraction (p. 25) - Of or involving muscular contraction in which the muscle remains under relatively constant tension while its length changes.

FIGURE 2.1 Single stimulus and muscle twitch.
(a) Opening screen of the Single Stimulus experiment. (b) The muscle twitch: myogram of an isometric twitch contraction.
(PhysioEx 8.0 for A&P: Laboratory Simulations in Physiology. Pearson Learning Solutions).

Activity 1: Practicing Generating a Tracing

No Data for This Activity (practice generating tracings)

No Questions For This Activity

Summary:
In this Activity, I learned how to produce a tracing of muscle activity following stimulation.

Activity 2: Determining the Latent Period

Data:

Questions:

2-1: How long is the latent period? In other words, how much time elapses before the active force reading moves? __2.78____ msec

2-2: What occurs in the muscle during this apparent lack of activity? (Hint: something IS occurring; see p. 18)
During the latent period calcium is being released from the sacroplasmic reticulum; which stores ATP, and filament movement is taking up slack.

Summary:

In this Activity, I learned/observed that: During the brief latent period the stimuli is circulating and sending signals for an appropriate response. The electrical signal gets passed up the cell membrane and other channels open.

Activity 3: Investigating Graded Muscle Response to Increased Stimulus Intensity

Data:

Questions:

3-1: What is the minimal, or threshold stimulus? In other words, when does active force start? __ around 0.8 ___ V

3-2: What is the maximal stimulus? In other words, when is the stimulus maximized (not the highest it can go but the highest active force you see)? __8.0______V

3-3: How can you explain the increase in force that you observe?
Stimulus intensity is the strength of the apmlitude of the stimulus. Stimulus frequency is the number of times per unit time that the stimulus is presented. In some cases it takes more intensity to get the reaction needed.

Summary:

In this Activity, I learned/observed that: All cells, including nerve and muscle cells, have an electrical gradient across their cell membranes, with the inside of the cell being negative with respect to the outside at rest.

Activity 4: Investigating Treppe

Data:

Questions:

4-1: What happens to force production with each subsequent stimulus? Force _increases__ (increases, decreases, stays the same - choose one) with each subsequent stimulus.

Summary:

In this Activity, I learned/observed that: Treppe is an increase in the force generated by a muscle fiber as it warms up. This is due to the increase in temperature because of an increase in cell activity. Enzymes and become more efficient at a slightly higher temperature.

Activity 5: Investigating Wave Summation

Data:

Questions:

5-1: Is the peak force produced in the second contraction greater than that produced by the first stimulus? Yes

5-2: Is the total force production even greater? Yes

5-3: In order to produced smooth, sustained muscle contraction at Active Force = 2 gms, do you think you will need to increase or decrease the voltage? Decrease voltage

5-4: At what voltage were you able to achieve Active Force = 2 gms? _1.7-2.5_ V (depending on how fast was clicking)

5-5: How does the frequency of stimulation affect the amount of force generated by the muscle? Hint: Compare the force generated from a single click and from rapidly clicking "Single Stimulus" several times. Increased frequency causes ___increased_____(increased, decreased, the same - choose one) force to be generated by the muscle.

Summary:

In this Activity, I learned/observed that: Summation is the combination of responses two or more stimuli applied to a muscle (or motor unit) in quick succession. The two responses combine to produce a greater muscle tension than what you see with just a single stimuli.

Activity 6: Investigating Fusion Frequency/Tetanus

Data:

Questions:

6-1: Describe the appearance of the tracing. Specifically, discuss the force appearance.

6-2: How do the tracings change as the stimulus rate is increased? Increased stimulation rate causes __increased__ (increased, decreased, the same - choose one) active force; this is demonstrated by ___smoother___ (smoother, rougher, the same - choose one) peaks shown on the tracings.

6-3: From your graph, estimate the stimulus rate above which there appears to be no significant increase in force: ___120______ stimuli/sec

6-4: What stimulus intensity produced smooth (active) force at Force = 2 gms? _1.2_V

6-5: What intensity produced smooth contraction at Force = 3 gms? __1.6___V

6-6: Explain what must happen to the intensity and frequency of the stimulus to achieve smooth contraction at different force levels. Increased stimulation rate creates ___smoother____ (smoother, rougher, the same - choose one) contraction and decreased voltage means that ___less______ (more, less, the same - choose one) force is produced.

Summary:

In this Activity, I learned/observed that: The muscle tightening up can cause severe pain as well as damage. If you have the “lockjaw” symptom it can easily had the additional spasms in the chest, back, neck and abdomen.

Activity 7: Investigating Muscle Fatigue

Data:

Questions:

7-1: Why does the force begin to decrease with time? Note that a decrease in force indicates muscle fatigue. (Hint: think about what a muscle needs to contract).
The muscle force decreases because the muscle is consuming ATP faster than it is being produced.

7-2: Turning the stimulator off allows a small measure of recovery. The muscle will produce force for a longer period if the stimulator is briefly turned off than if the stimulations were allowed to continue without interruption. Explain why.
When the stimulator is turned off the muscle is able to catch up a little with ATP production

7-3: Describe the difference between the current tracing and the myogram generated in step 6. The second tracing shows faster fatigue than the tracing in which the stimulator was turned on and off.

Summary:

In this Activity, I learned/observed that: Fatigue is a feeling of exhaustion or loss of strength. Even though most discuss the muscle fatigue, the body can tire of prolonged work in other ways. Fluid loss, mainly sweat, is a major factor. The heart is a muscle, and so are the muscles used in breathing and they are also able to become fatigued.

Activity 8: Investigating Isometric Contraction

Data:

Questions:

8-1: What happens to the passive and active forces as the muscle length is increased from 50 mm to 100 mm? Specifically, discuss what the force looks like at particular lengths - at what lengths did the force show large increases or decreases.

Passive force: As the muscle length is increased from 50 mm to 100 mm, the passive force is initially zero and then, at approximately 84 mm, begins to sharply rise.

Active Force: As the muscle length is increased from 50 mm to 100 mm, the active force increases steadily until a muscle length of 75mm and then begins to fall with increasing muscle length.

Total force: As the muscle length is increased from 50 mm to 100 mm, the total force initially rises, then, at a muscle length of 76 mm, begins to fall, and finally, at a muscle length of 94 mm rises again producing a dip in the curve.

8-2: Explain the dip in the total force curve. (Hint: Keep in mind you are measuring the sum of active and passive forces).
Because the total force curve is the result of the numerical sum of the active and passive force data points, we see a rise on the left side of the total force due to the rise in the active force. The passive force has no influence in the rise on the left side. The total force curve begins to fall because the active force falls. The total force does not fall as fast as the active force because the passive force is simultaneously rising. The sharp increase at the right side of the total force curve is almost entirely due to the passive force.
Summary:

In this Activity, I learned/observed that: Isometrics are a type of strength training in which the joint angle and muscle length do not change during contraction. They are done in static positions, rather than being dynamic through a range of motion. A maximal isometric contraction falls to half or less in the first minute, and starting at 70-80% maximum force retards the subsequent decline only a little.

Activity 9: Investigating the Effect of Load on Skeletal Muscle

Data:

Questions:

9-1: What do you see happening to the muscle during the flat part of the tracing? Click "Stimulate" to repeat if you wish to see the muscle action again.
During the flat part of the tracing, the muscle rises from the surface of the platform and then descends again

9-2: Does the force the muscle produces change during the flat part of the tracing (increase, decrease, or stay the same)?
The force production does not change during the flat part of the tracing. It stays the same.

9-3: Which of the two weights used so far results in the highest initial velocity of shortening?
Weight_1.5____ g
Velocity _0.45___mm/sec

9-4: Repeat step 6 for the remaining two weights:
Weight __1.0___g
Velocity__1.34___ mm/sec

Weight __2.0___g
Velocity __0.0___mm/sec

9-5: What does the plot reveal about the relationship between resistance and the initial velocity of shortening? Increased resistance causes __shorter____ (shorter, longer, the same - choose one) initial velocity of shortening.

9-6: Describe the relationship between starting length and initial velocity of shortening.
As the starting length of the muscle is increased from 60 mm to 90 mm, the initial velocity of shortening first increases and then decreases.

Summary:

In this Activity, I learned/observed that:  write 1-2 sentences on what you observed by doing this experiment – think “big picture" That more of the muscle fibres are being called into action simultaneously at the end of an exercise phase than at the beginning. It is as if the nervous system has been teaching itself how to get the most force out of the muscle bulk it already has available to it.