Stimulus Strength and Response in Muscle Fibers

A study of stimulus strength and response, muscle length and tension generated, and contraction strength in gastrocnemius muscle of frogs.

Introduction:

 

The amount of tension in muscles changes based on how many muscle fibers are contracting. When stimulus strength is increased beyond maximal level, tension does not continue to increase because all of the muscle fibers in the muscle are contracting (Hill, Wyse, & Anderson, 2018). The resting length of skeletal muscles maximizes the muscle’s contraction when stimulated (Hill at al., 2018).

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The objective of stimulus-response exercise was to determine the relationship between the strength of the stimulus and the response of the muscle. The length-tension relationship exercise was performed to determine the relationship between muscle length and tension generated in the muscle. The objective of the summation and tetanus was to measure the amplitude of contraction produced in a muscle that is stimulated with repeated pulses delivered at progressively higher frequencies. The objective of the pre- and post-loaded weight and contractile strength exercises were to measure the strength of contraction while the muscle was lifting pre-loaded and post-loaded weights.

 

Methods and Materials:

 

Figure 1:  Set-up for weight and work exercises acquired from Animal Muscle -Skeletal Muscle-Weight and Work-SetupIXTA page AM-1-4 used to produce and record contractions from the frog gastrocnemius muscle.

Figure 2: The equipment setup used to induce and record contractions from the frog gastrocnemius muscle related to length and tension of muscle using IXTA data acquisition unit and power supply.

The frogs were placed in an ice bath for ~15 minutes to anesthetize them. The frogs were then pinned down in a dissection tray and their skin was removed from the legs using scissors, forceps, and a scalpel. Steps for frog gastrocnemius were followed from a video titled Frog Dissection on YouTube. Ringer solution was used to moisten the muscle. The femur bone was clamped to the ring stand holder and a fishing hook was used to attach the Achilles tendon to transducer. The stimulating electrodes were positioned against the muscle about partway between the knee and the tendon as illustrated in Figure 2. The FT-302 Force Transducer was calibrated with no weight and 5 grams.

 

Results:

 

Table 1: Amplitude of muscle twitches generated by stimulus pulses of different amplitudes.

Stimulus Amplitude (V)

Twitch Amplitude (g)

0.000

0.000

0.250

0.000

0.500

2.769

0.750

10.288

1.000

12.046

1.250

20.750

1.500

28.257

1.750

49.130

2.000

60.014

2.250

63.854

2.500

63.944

2.750

68.599

3.000

70.347

3.250

73.564

3.500

79.990

3.750

81.064

4.000

80.645

4.250

83.224

4.500

85.355

Figure 3: Amplitude of muscle twitches (g) generated by stimulus pulses of different amplitudes (V).

Table 2: Muscle length and muscle twitch amplitude for the frog gastrocnemius muscle.

Muscle Length (mm)

Twitch Amplitude (g)

34

2.267

36

36.86

38

64.749

39

87.307

40

59.11

41

54.914

42

7.202

43

5.494

Figure 4: Muscle length (mm) and muscle twitch amplitude (g) for the frog gastrocnemius muscle. The active tension segment and passive tension segment are labeled, respectively.

 

Table 3: Amplitude and times of muscle twitches generated by stimulus pulses of different amplitudes.

 

Muscle Twitch

Stimulus Amplitude (V)

Amplitude (g)

Contract Time (msec)

Relax Time (msec)

Latency (msec)

0.000

0

0

0

0

1.000

99.955

95

160

20

2.000

112.588

100

175

25

3.000

121.634

105

195

25

4.000

124.295

105

180

25

5.000

128.733

105

195

25

6.000

128.766

105

215

25

7.000

128.515

105

210

25

 

Table 4: Strength of muscle contractions during mechanical summation and tetanus.

Stimulus Frequency (Hz)

Amplitude 1st Twitch (V)

Maximum Amplitude (V)

Change in Passive Tension (V)

Summation/Tetanus

0.5

124.612

126.05

0

No

1

120.376

122.636

0

No

2

116.017

116.812

0

No

3

111.796

118.150

81.975

Summation

4

108.676

120.282

113.929

Incomplete tetanus

5

108.604

122.611

121.033

Incomplete tetanus

10

139.881

143.591

143.098

Incomplete tetanus

20

145.456

145.456

145.456

Complete tetanus

30

146.079

146.079

146.079

Complete tetanus

 

 

Table 5: Amplitudes and times of contractions from a post-loaded muscle.

Rod displacement: 19 mm; trace deflection: 1,859 mV; conversion factor: 0.01

 

Muscle Twitch

Post-load Weight (g)

Amplitude (mV)

Distance (mm)

Contraction Time (msec)

Relaxion Time (msec)

Latency (msec)

Work (Weight x Distance)

Rate of Contraction (Amplitude /Contraction Time)

10

164

1.64

95

65

35

16.4

1.73

20

154

1.54

80

65

35

30.8

1.93

30

138

1.38

90

65

50

41.4

1.53

40

128

1.28

80

60

50

51.2

1.60

50

114

1.14

65

50

35

57.0

1.75

60

106

1.06

75

45

35

63.6

1.41

70

97

0.97

65

45

45

67.9

1.49

 

Table 6: Amplitudes and times of contractions from a pre-loaded muscle.

Rod displacement: 19 mm; trace deflection: 1,859 mV; conversion factor: 0.01

 

Muscle Twitch

Pre-load Weight (g)

Amplitude (mV)

Distance (mm)

Contraction Time (msec)

Relaxion Time (msec)

Latency (msec)

Work (Weight x Distance)

Rate of Contraction (Amplitude /Contraction Time)

10

215

2.15

90

65

40

21.5

2.39

20

199

1.99

80

60

35

39.8

2.49

30

195

1.95

95

65

30

58.5

2.05

40

192

1.92

80

65

40

76.8

2.40

50

187

1.87

100

55

45

93.5

1.87

60

177

1.77

100

50

35

106.2

1.77

70

164

1.64

90

60

45

114.8

1.82

 

 

Figure 5: Work plotted against load weight, both pre- and post- load.

 

Discussion and Conclusions:

 For the stimulus response exercise, the twitch amplitude increased from 0.500 V stimulus amplitude up to of 3.750 V, and decreased at 4.000 V. This data agrees with the expected results because a small amplitude was produced when a weak stimulus was applied due to the contraction of only some fibers. Additionally, when a strong stimulus was applied, all of the muscle fibers contracted, which caused a large amplitude. At 0.250 V, the twitch amplitude response was 0.000 mV because few channels were open, which was not enough to produce an action potential that reached threshold. The length-tension exercise results were supported by literature. As the muscle length increased to normal resting length for a frog, the overlap of the thick and thin filaments increased optimal cross-bridge binding with actin. Twitch amplitude decreased as length increased past moderate muscle lengths because sarcomeres had less overlap of thick and thin filaments (Hill at al., 2018).

 In the mechanical summation and tetanus exercise, once mechanical summation was present, the change in passive tension increased as stimulus frequency increased until the maximum amplitude and change in passive tension were equal. Tetanus was observed at high stimulus frequencies of 20 and 30 Hz because the reuptake of calcium is very fast. An increase in cytosolic calcium levels activates muscle contraction (Kuo & Ehrlich, 2015). Muscle relaxation is slower after tetanus compared to after a single muscle twitch because there is a larger amount of calcium that needs to go back to the sarcoplasmic reticulum.

Literature Cited:

 

Hill, R. W., Wyse, G. A., Anderson, M. (2018). Animal physiology. Oxford University Press, NY.

Kuo, I. Y., & Ehrlich, B. E. (2015). Signaling in muscle contraction. Cold Spring Harbor perspectives in biology, 7(2), a006023. doi:10.1101/cshperspect.a006023

 

Macroeconomic Analysis of the US Economy: Stimulus Package

In macroeconomics we focus on the United States economy as a whole rather than the smaller pieces that make it up. We also analyze the overall cause and effect of certain situations in order to further understand how these items affect the economy on a short-term and long-term basis. It is important to understand these things as a member of such a large society as it helps create a better idea of our specific roles at this time. When trying to select a topic that would best directly reflect the economy as whole and the impact that any decision could have on the overall well being of its people, what better topic of discussion than the 2009 economic stimulus plan.

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The 2009 economic stimulus plan being implemented under the Obama administration is titled the American Recovery and Reinvestment Act of 2009 abbreviated as ARRA. This package was signed by President Obama on February 17, 2009. The current focus of the stimulus plan is economic expansion. The plan focuses on the current state of the economy while trying not to damage future funds and spending. A few key things of importance in the stimulus plan are health care, creation of new jobs, and new resources for energy. This 787 billion dollar plan strives to pull the economy out of its current recession in hopes of healing the global community.
The American Recovery and Reinvestment Act of 2009 is the biggest stimulus plan put into place since the Roosevelt Administration. The importance of this plan is its overall impact in the United States. If the plan follows through in accordance with the incentives proposed, the economy should feel a breakthrough from the recession. On the contrary, if implemented too quickly, it may cause a reverse effect and draw the economy into a greater recession. It is important to discuss the stimulus plan as it directly affects the citizens of this country. We wanted a topic that would educate us as well as provide information supportive of macroeconomics and the broader topic. The American Recovery and Reinvestment Act of 2009 is an important topic of discussion as it evaluates and analyzes the current economic crisis and the things the government needs and wants to do in order to satisfy the needs of its current members.
In the economic stimulus plan of 2008 and the extended version American Recovery and Reinvestment Act of 2009 & 2010, are solutions to reinvest in the economy from different tax use aspects. The Government uses fiscal policy tools as a solution to the economic recession, just as in the Great depression. This time around tax cuts returned in the form of stimulus checks are being used to increase consumption and investment in U.S. goods. Due to the fact that our economy is at an exceptionally large deficit, a plan that would help decrease taxes in the current 2010 year would be ideal. Structural explanations for the solutions that the Government applies are Keynesian Economics. One of the theories associated with Keynesian economics is the expansionary fiscal policy which explains what happens when government spending increases. The following formula further explains this theory; (G á ðADá [C+I +Gá+NX] (TâðADá [Cá+ Iá+G+NX]) taxes reduced increase aggregate demand. The 2008 stimulus plan was much less complex than the ARRA. Comparing total cost and distributions, the 2008 bill only cost 150 billion dollars. The 2008 stimulus plan didn’t have a huge effect on the economy as it only increased consumption by 3% due to a prolonged process in the distribution of stimulus checks. The American Recovery and Reinvestment act of 2009 specifies that 37% of the package is to be devoted to tax cuts that are equivalent to approximately 288 billion dollars. 18% of the package or 144 billion dollars is being given for state and local fiscal relief. 45% of the package or 357 billion dollars is being given to social and spending programs on a federal level.
In comparison to the 2008 stimulus plan, this plan serves a much broader sector of the economy as billions of tax dollars are being presented to local state fiscal relief, health care, education, infrastructure, developments in science and a few of other areas. The American Recovery and Reinvestment act of 2009 is still in progress until 2010, so the effects are still unpredictable as to how the economy will be affected until the process is complete. It’s probably safe to say that tax reduction is the most important portion in the stimulus plans process as it will increase the overall aggregate demand and spending amongst the U.S. citizens.
In addition, considering the fact that our country has plummeted into recession, this package is said to help the economy recover from its detrimental state. According to hubpages.com the main focus of the ARRA is to increase consumer consumption, investment and spending in the market. This package also co-exists with Fiscal policies, Budget deficits and Debt. The president is considering using two fiscal tools to help improve the economy which include government spending, and taxes illustrated in chapter 8 of the Macroeconomics brief edition book. The government accumulated an 819 billion dollar budget in order to spend on the entire stimulus package. This is a prime example of Discretionary fiscal policy. This policy explains the significant changes in government spending and collection of taxes, which also explains the current billon dollar budget being proposed by the government. These processes are a few ways to help our economy move toward expansion. With government spending increasing this causes a reduction in taxes. When taxes are decreased, it leaves consumers more money to spend on goods and services, causing an increase in the overall aggregate demand. In increase in the overall demand of goods and services helps regenerate the economy in an effort to push it out of the recession. In addition, an overall increase in consumer spending will allow the government to pull government spending from certain areas as consumers become more optimistic about the economy. Something the American Recovery and Reinvestment Act of 2009 definitely wants to avoid is the Crowding Out Effect. When there is fiscal expansion through an increase in interest rate, aggregate demand is forced to decrease. An example of the crowding out effect is the current lack of investment, such as fewer people are purchasing homes.
The American Recovery and Reinvestment Act of 2009 is looking towards an expansionary policy. The proof is clearly defined in the different measures associated with the bill. Being that the government is spending money at all in an effort to help the economy is an obvious sign of expansionary fiscal policy. The ARRA is pushing for an increase in government spending and decrease in taxes. These are two aspects that describe expansionary policy as explained in chapter 8.
The current United States government debt is set at 11.4 trillion dollars and steadily rising. Looking at the fact that the Obama Administration plans to spend an additional 787 billion dollars of what the government already doesn’t have, it is believed that this is not the best of ides. There are many concerns associated with the stimulus package and its long-term effects on the U.S. economy. The two main concerns being listed as the stimulus package not working, and even if it does work that the plan could still be problematic. More than anything the concern is that if the U.S deficit expands too quickly it will require the government to borrow internationally. According to the Council on Foreign Relations, “if the government starts borrowing internationally, it will in turn weaken the U.S. geopolitical strength and increase the risk of the U.S. defaulting in on its international debt and facing a true financial meltdown.” Adversely the stimulus plan has the potential to bring the community back to a normal state. Jason Furman, the senior economic advisor during Obama’s campaign, argues that the stimulus plan need be:
Timely so that it guarantees that spending affects the economy when it is needed the most, and in order to prevent overexpansion or rapid inflation
Targeted to ensure that ach dollar being spent is used to its maximum potential in the gross domestic product and helps the people most effected by the current state of the economy and,
Temporary in order to prevent unnecessary strain on the country’s budget in the long-run
Overall, many economist feel as though the stimulus package is headed in the right direction as it focuses on the many things affecting the people most effected by the country’s recession. Tyler Cowen, an economic blogger, recently wrote that Obama’s plan appears to take into account the frightening possibility of the U.S. defaulting on its international debt, in turn explaining why the stimulus package isn’t any larger.
In conclusion, we have to come to understand not only the overall purpose of the stimulus package but also the effects that it may have on the economy in the long-run. It has been brought to our attention that although the efforts of the stimulus package are to push the economy towards expansion, it is going to require the members of this country to be more optimistic about the economy. The measures established in the American Recovery and Reinvestment Act of 2009 provide information regarding the expected direction the U.S. government is pushing for the economy to go. The Obama Administration plans to put 75 billion dollars into the economy by implementing tax cuts and pushing direct spending directly to the people who need it the most.