Question

muscles and muscle tissue

1. correctly relate the story of contraction events in a muscle fiber by numbering each event below. the first step is indicated (number 1).

______ 1. myosin heads bind to active sites on actin molecules.
______ 2. atp is hydrolyzed.
______ 3. myosin heads return to their high - energy shape (cocked), ready for the next working stroke.
__1_ 4. calcium ions bind to troponin.
______ 5. cycling continues until calcium ions are sequestered by the sr.
______ 6. myosin cross bridges detach from actin.
______ 7. troponin changes shape.
______ 8. adp and $p_i$ (inorganic phosphate) are released from the thick filament.
______ 9. myosin heads pull on the thin filaments (working stroke) and slide them toward the center of the sarcomere.
______ 10. atp binds to the thick filament.
______ 11. tropomyosin is moved into the groove between the f - actin strands exposing active sites on actin.

1. relative to general terminology concerning muscle activity, first, label the following structures on figure 9.5: insertion, origin, tendon, resting muscle, and contracting muscle. next, identify the two structures named below by choosing different colors for the coding circles and the corresponding structures in the figure.

$\bigcirc$ movable bone
$\bigcirc$ immovable bone

Explanation:

Question 6 (Muscle Contraction Event Ordering)

Step 1: Recall the Sliding Filament Theory Steps

The correct order of muscle contraction events (after step 1: Calcium ions bind to troponin) is based on the sliding filament theory. Let's list the correct sequence:

1. Calcium ions bind to troponin (given as step 4, number 1).
2. Troponin changes shape (step 7).
3. Tropomyosin is moved to expose active sites on actin (step 11).
4. Myosin heads bind to actin active sites (step 1).
5. ADP and \( P_i \) are released (step 8).
6. Myosin heads pull (working stroke, step 9).
7. ATP binds to myosin (step 10).
8. Myosin cross - bridges detach (step 6).
9. ATP is hydrolyzed (step 2).
10. Myosin heads return to cocked position (step 3).
11. Cycling continues until \( Ca^{2+} \) is sequestered (step 5).

Now let's number each event:

• Event 1: Myosin heads bind to active sites on actin molecules. → 4 (after step 11)
• Event 2: ATP is hydrolyzed. → 9 (after step 10)
• Event 3: Myosin heads return to their high - energy shape (cocked), ready for the next working stroke. → 10 (after step 9)
• Event 4: Calcium ions bind to troponin. → 1 (given)
• Event 5: Cycling continues until calcium ions are sequestered by the SR. → 11 (last step)
• Event 6: Myosin cross bridges detach from actin. → 8 (after step 10)
• Event 7: Troponin changes shape. → 2 (after step 4)
• Event 8: ADP and \( P_i \) (inorganic phosphate) are released from the thick filament. → 5 (after step 4)
• Event 9: Myosin heads pull on the thin filaments (working stroke) and slide them toward the center of the sarcomere. → 6 (after step 5)
• Event 10: ATP binds to the thick filament. → 7 (after step 6)
• Event 11: Tropomyosin is moved into the groove between the F - actin strands exposing active sites on actin. → 3 (after step 2)

So the correct numbering from 1 - 11 (with step 4 as 1) is:

1. Calcium ions bind to troponin. → 1
2. Troponin changes shape. → 2
3. Tropomyosin is moved into the groove between the F - actin strands exposing active sites on actin. → 3
4. Myosin heads bind to active sites on actin molecules. → 4
5. ADP and \( P_i \) (inorganic phosphate) are released from the thick filament. → 5
6. Myosin heads pull on the thin filaments (working stroke) and slide them toward the center of the sarcomere. → 6
7. ATP binds to the thick filament. → 7
8. Myosin cross bridges detach from actin. → 8
9. ATP is hydrolyzed. → 9
10. Myosin heads return to their high - energy shape (cocked), ready for the next working stroke. → 10
11. Cycling continues until calcium ions are sequestered by the SR. → 11

Question 7 (Muscle Terminology and Bone Labeling)

• Movable bone: The insertion of a muscle is on the movable bone. So the movable bone is associated with the insertion of the muscle. In the context of muscle action, when a muscle contracts, the movable bone moves.
• Immovable bone: The origin of a muscle is on the immovable bone. The immovable bone provides a fixed point for the muscle to act from.

For the labeling:

• Movable bone: The bone to which the muscle's insertion is attached (the bone that moves when the muscle contracts, e.g., in the arm, the radius/ulna during elbow flexion is the movable bone relative to the humerus).
• Immovable bone: The bone to which the muscle's origin is attached (the bone that does not move much during the muscle's contraction, e.g., the humerus in elbow flexion).

Answer:

(Question 6):
The correct numbering of the events is:

1. Myosin heads bind to active sites on actin molecules. → \(\boldsymbol{4}\)
2. ATP is hydrolyzed. → \(\boldsymbol{9}\)
3. Myosin heads return to their high - energy shape (cocked), ready for the next working stroke. → \(\boldsymbol{10}\)
4. Calcium ions bind to troponin. → \(\boldsymbol{1}\)
5. Cycling continues until calcium ions are sequestered by the SR. → \(\boldsymbol{11}\)
6. Myosin cross bridges detach from actin. → \(\boldsymbol{8}\)
7. Troponin changes shape. → \(\boldsymbol{2}\)
8. ADP and \( P_i \) (inorganic phosphate) are released from the thick filament. → \(\boldsymbol{5}\)
9. Myosin heads pull on the thin filaments (working stroke) and slide them toward the center of the sarcomere. → \(\boldsymbol{6}\)
10. ATP binds to the thick filament. → \(\boldsymbol{7}\)
11. Tropomyosin is moved into the groove between the F - actin strands exposing active sites on actin. → \(\boldsymbol{3}\)