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VIRTUAL MUSCLE STIMULATION ACTIVITY Go to: http://glencoe.mcgraw-hill.com/sites/dl/free/0078757134/383958/BL_21.html Read the Purpose and Objectives of the activity. Click on the blue Information button on the bottom right. Answer the following questions: 1. Contrast voluntary and involuntary muscles. Include what types of muscles are in each category and where these muscles are found. Both cardiac and smooth muscles are called “involuntary” because their contractions cannot be consciously controlled. Cardiac muscle exists only in the heart and contracts approximately 70 times per minute to pump blood throughout a body's circulatory system. Smooth muscles line many internal organs such as the trachea, intestines, and bladder. Smooth muscles contract and relax slowly, exerting and releasing pressure on the organs they surround. Skeletal muscles are the muscles that are used for movement. They are called “voluntary” muscles because their contractions are consciously controlled. 2. What attaches muscle to bones? Tendons 3. What is the “all or none” law of muscle contraction? When exposed to stimuli from the nervous system, each individual muscle fiber will contract either completely or not at all. 4. How is the strength of the muscle contraction determined? By the number of individual muscle fibers that respond to a stimulus. 5. Define a muscle twitch: If a single, quick electrical stimulus is applied to a skeletal muscle, the muscle will respond by contracting and relaxing quickly. 6. Define a muscle’s “threshold of stimulation:” The weakest electrical stimulation (measured in volts) required to cause a muscle to twitch. 7. Define the “point of muscle overload:” As the workload on a muscle increases, the muscle will eventually reach a point at which it will no longer be able to contract, no matter how much electrical stimulation it receives. Finish reading the information and then close the Information window. Follow the Procedure and record your data in the Table below. After you finish the experiment, answer the Analysis questions. TABLE 1 – Threshold Stimulus (V) LOAD LOWER FORELIMB MUSCLES UPPER FORELIMB MUSCLES CALF MUSCLES THIGH MUSCLES 0g 2.0 3.0 5.0 6.0 5g 3.0 4.0 5.5 6.5 10g 4.0 5.0 6.0 7.0 20g none 7.0 7.0 8.0 40g none None 8.0 9.0 80g none none none 10.0 ANALYSIS: 1. Based on the results of your investigation, what conclusions can you draw about the relationship between a muscle's workload and its threshold of stimulation? As the load doubles, the threshold stimulus usually increases by 1. A muscle that has a higher threshold of stimulation with no workload can handle a much higher workload. 2. Why would a muscle's threshold of stimulation change as its Workload changes? It would require more stimulation in order to contract. The muscle essentially has to work harder to get a contraction. 3. Which muscles were able to contract under the greatest loads? What does this suggest about the role these muscles play in frog movement? The calf and thigh muscles could contract with the greatest loads. These muscles are required for the frog to leap and need to bear the weight of the frog while causing the frog to jump. 4. Describe an experiment you might perform to determine which leg muscles of a frog are important for jumping long distances. Answers will vary. 5. What are some advantages of performing this experiment in a simulated environment? Each muscle can be isolated easily and a simulation does not hurt the animal.