Module 6 Intro

Module 6—The Motor System and Homeostasis

Energy for Muscle Contraction

 

The body’s muscles require a continuous supply of energy in order to maintain their function. When the energy demands for muscle contraction exceed the reservoir of stored energy, the ability to control movements may be impaired to the point that normal voluntary coordination of even simple tasks like running are impossible.

 

You can find a number of videos on the Internet outlining the effects of extreme depletion of energy reserves in two competing triathletes as they approach the finish line of the 1997 Ironman World Championship. These videos are quite compelling and may be found using the key words “1997 ironman crawl.”

 

Muscle contraction requires a continuous supply of energy in the form of ATP. There are three main sources of this energy—one of which is new to you:

• creatine phosphate (sometimes referred to as the phosphagen system)
  
  
• aerobic respiration
  
  
• fermentation (also known as anaerobic respiration and/or as the lactic acid system)

Review the mechanisms by which the energy is supplied through creatine phosphate, aerobic cellular respiration, and fermentation by looking at the following diagram and reviewing what you learned in Unit C. Reading “Energy for Muscle Contraction” on pages 339 to 342 of the textbook may also be beneficial.

 

Self-Check

 

SC 5. Once you are clear on the differences described in the diagram, complete the following summary table. This table compares the three sources of energy for muscle contraction.

 

Energy Source	Aerobic or Anaerobic	Site of Reaction	Initial Reactant Required for Contraction	Final Products of Reaction	Relative Amounts of ATP Produced
Creatine Phosphate
Aerobic Cellular Respiration
Fermentation

 

 

During prolonged endurance exercise—such as running a marathon—a depletion of muscle sugar stores, a decrease in blood glucose, dehydration, or an increase in body temperature contribute to fatigue. During intense muscular activity, such as short-distance running, lactic acid is formed through glycolysis and lactic acid fermentation.

 

The H+ ions from lactic acid decrease the pH of the muscle; this may inhibit metabolic processes, Ca2+ fluxes, and ATP activity, and thereby decrease work output. The reason why you experience pain while having a muscle cramp is because your muscle has stopped functioning properly. This is a mechanism designed to allow your body to recover the oxygen debt that has occurred. If you are in pain, you generally stop using the muscles.

 

Try This

 

TR 3. Energy Supply During an Activity

 

How and when are the different sources of muscle metabolism that you already know about—creatine phosphate (the phosphagen system), aerobic respiration, and anaerobic respiration (lactic acid system)—used during exercise? Why is heat produced in the muscles during exercise? You may need to do further research.

 

Prepare a step-by-step summary of how the body is supplied with energy over the course of exercising. Keep in mind how ATP is supplied to the muscle cells over the first few seconds, minutes, and eventually longer portions of a workout. Also, show the relationship between heat production and muscle use. You may use a variety of formats such as a slide show, a podcast, a poster, a diagram, or a paragraph to present your summary.

 

You will find directions and marking guidelines in your Lesson 1 Assignment.

 

Self-Check

 

SC 6. Click here to complete a quiz.

 

Biology 20 © 2008 Alberta Education