EGRB 209 Homework #3 1. Muscle Force (6 points) a. What are the three ways that the body varies muscle force? b. Which method has the biggest effect and which has the least? 2. Active Tension in Muscles (10 points) a. What is active tension? b. How does it vary with length of the muscle? Include details on how the microstructure of the muscle cell contributes to active tension. 3. Consider muscle fibers that are 16 cm long and that develop a maximum of 20 N/cm² force. The muscle has a volume of 140 cm³ with the fibers aligned in the direction of the tendon. (hint: muscle force = Σ= N¿A¿F¸, where N = innervation ratio, A =cross-sectional area per muscle fiber, and Fs = force per unit area of muscle fibers) (12 points) a. What is the maximum force developed by this muscle? b. partial recruitment results in activation of 20% of the muscle fibers (assuming they are all of equal size), how much force could the muscle generate? c. If the muscle fibers contract 15% of their length in 70 ms under no load, what is the maximum muscle velocity? 4. Muscular Force Generation (15 points) a. Describe the Cross-bridge cycle. b. How many ATP are used per cycle? c. How does Calcium effect/control the cross-bridge cycle? 5. Synapse A on a motor neuron has an EPSP with a peak depolarization of 3 mV. Synapse B has an EPSP with a peak depolarization of 2 mV. Synapse C results in an IPSP with a peak hyperpolarization of 2.5 mV. The resting potential of the nerve is -70mV, assume threshold is -59 mV. (12 points) a. Simultaneous firing of A and B results in what peak potential? What is this phenomenon called? Is this enough to reach threshold? b. Simultaneous firing of B and C results in what peak potential? What is this phenomenon called? Is this enough to reach threshold? c. What is the peak potential of simultaneous firing of 6 A, 10 B, and 8 C synapses? Is this enough to reach threshold? 6. Neuromuscular Junctions (10 points) a. How is an action potential on a neuron transferred to an action potential on a Muscle? b. What is Excitation-Contraction Coupling? 7. Valeria is a well-trained endurance athlete, and she is currently training for her next marathon. She needs to run 15 miles in one day as part of her training routine but she doesn't have the time to do all 15 at once and her schedule is packed that day with back to back meetings all day. She decides to split her run up and goes out for a 5 mile morning jog at an elevated pace (6 min/mile), which ultimately requires 2.5 mol of ATP per minute. 12 hours later Valeria runs the remaining 10 miles. She attempts to run slower than her average pace at 8 min/mile, but she cannot maintain and she drops to an 11 min/mile in the last 2 miles. This run ultimately consumes an average of 1.5 mol of ATP per minute. (10 points) a. How much ATP did Valeria use during her runs? b. If Valeria's muscles are capable of consuming 220 mols of ATP in one run, what are some reasons why Valeria experience fatigue toward the end of her evening run? 8. Lactic acid production is increased when the demand for ATP outpaces oxidative phosphorylation and intensity of exercise increases. Describe three ways lactic acid can be recycled? (9 points) 9. Complete the following table comparing Fast-twitch vs Slow-twitch muscle fibers (16 points) General size of fiber (small or large) Speed of Cross-bridge cycle Type of Metabolism (glycolic vs oxidative) Relative amount of Mitochondria Example of exercise that uses each fiber Which fiber would consume more ATP per min, assuming both are active? Which fiber has a slower velocity? Which fiber has more power? Slow Twitch Fibers Fast Twitch Fibers