PEX-02-06

Exercise 2: Skeletal Muscle Physiology: Activity 6: The Skeletal Muscle Length-Tension Relationship Lab Report Pre-lab Quiz Results You scored 80% by answering 4 out of 5 questions correctly. 1. During an isometric contraction You correctly answered: d. the skeletal muscle is generating force, but it remains at a fixed length. 2. The force that results from muscles being stretched is You correctly answered: a. passive force. 3. Active force You correctly answered: b. is determined by the amount of myosin bound to actin. 4. When you generate the isometric length-tension curve, which of the following forces will not be indicated on your screen? You correctly answered: c. tetanic force 5. Passive force in skeletal muscle is largely caused by Your answer : d. the bungee cords. Correct answer: c. the protein titin.

03/19/13

page 1

Experiment Results Predict Question: Predict Question: As the resting length of the muscle is changed, what will happen to the amount of total force the muscle generates during the stimulated twitch? Your answer : a. An increase in muscle length will increase total force. Stop & Think Questions: Note the dip in total force at a muscle length of 90 mm. Why does this occur? Your answer : a. At this muscle length, there is too much overlap of myosin and actin, which impairs active force production. Correct answer: d. At this muscle length, active force has decreased in value and passive force has not yet increased to a significant value. Experiment Data: Voltage 8.5 8.5 8.5 8.5 8.5 8.5 8.5 8.5 8.5

Length 75 70 65 60 55 50 80 90 100

Active Force 1.82 1.75 1.55 1.21 0.73 0.11 1.75 1.21 0.11

03/19/13

page 2

Passive Force 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.25 1.75

Total Force 1.82 1.75 1.55 1.21 0.73 0.11 1.77 1.46 1.86

03/19/13

page 3

03/19/13

page 4

03/19/13

page 5

03/19/13

page 6

03/19/13

page 7

03/19/13

page 8

Post-lab Quiz Results You scored 60% by answering 3 out of 5 questions correctly. 1. When a skeletal muscle is stimulated and generates force but remains at a fixed length You correctly answered: d. the muscle is contracting isometrically. 2. Which protein is mostly responsible for the development of passive force in a muscle? You correctly answered: d. titin 3. In skeletal muscle, active force stimulated through a range of muscle lengths Your answer: c. will always be the dominant value contributing to the total force of the muscle. Correct answer: b. will utilize ATP hydrolysis to drive the cross bridge cycle. 4. Which if the following is not depicted in a typical skeletal muscle isometric length-tension curve? You correctly answered: a. time 5. Maximal active tension will be produced in a skeletal muscle fiber when Your answer: c. the fiber is longer than its resting length. Correct answer: a. the fiber is at its resting length.

03/19/13

page 9

Review Sheet Results 1. What happens to the amount of total force the muscle generates during the stimulated twitch? How well did the results compare with your prediction? Your answer: Total force is altered by the starting resting length. My prediction was correct in that it would change either way, with either lengthening the muscle or shortening it, both methods changed the total force generated by the muscle. If the muscle is lengthened the passive force increases, and if the muscle is shortened the active force increases. With each force (a&p) the total force is changed depending on the amount of either A or P forces. 2. What is the key variable in an isometric contraction of a skeletal muscle? Your answer: The muscle is attached to a weight that exceeds its peak tension capabilities. On stimulation, tension will rise to a peak, but the muscle as a whole cannot shorten. 3. Based on the unique arrangement of myosin and actin in skeletal muscle sarcomeres, explain why active force varies with changes in the muscle's resting length. Your answer: Active force is generated from myosin thick filaments bind to thin actin filaments, engaging the cross bridge cycle and ATP hydrolysis. Active force data changes as the resting length of the muscle changes. When the resting length of the muscle is shortened, the active force amount increases. When the resting length of the muscle is lengthened, the active force amount decreases. The change in the active force amount is completely caused by the amount of myosis bound to actin. The shorter the muscle's resting length is, the more myosis filaments bind to actin filaments. 4. What skeletal muscle lengths generated passive force? (Provide a range.) Your answer: 80, 90, and 100. 5. If you were curling a 7-kg dumbbell, when would your bicep muscles be contracting isometrically? Your answer: At any point in which the bicep muscle remains at a fixed length. My best example is holding 2 dumbbells parallel to the floor and holding them in that position for 30 seconds. The muscles are contracting but are not shortening.

03/19/13

page 10