Exam Review: Muscles (Chapters 9 & 10)

1. If a muscle is stretched too far, fewer cross-bridges can form.

True

False

When a muscle is stretched too far, the sarcomeres within the muscle fibers are also stretched. This causes the actin and myosin filaments to move further apart, reducing the overlap between them. As a result, fewer cross-bridges can form between the actin and myosin, which are necessary for muscle contraction. Therefore, the statement that fewer cross-bridges can form when a muscle is stretched too far is true.

Explanation

When a muscle is stretched too far, the sarcomeres within the muscle fibers are also stretched. This causes the actin and myosin filaments to move further apart, reducing the overlap between them. As a result, fewer cross-bridges can form between the actin and myosin, which are necessary for muscle contraction. Therefore, the statement that fewer cross-bridges can form when a muscle is stretched too far is true.

2. Calcium binds on troponin on the _____ myofilaments

Calcium binds to the troponin complex, which is located on the actin myofilaments. The troponin complex consists of three subunits: troponin C, troponin I, and troponin T. Troponin C specifically binds to calcium ions. When calcium binds to troponin C, it causes a conformational change in the troponin complex, which allows the myosin heads to bind to the exposed binding sites on the actin filaments. This interaction between actin and myosin is essential for muscle contraction. G-actin refers to the globular form of actin, which is the monomeric subunit that polymerizes to form the filamentous actin (F-actin).

Explanation

Calcium binds to the troponin complex, which is located on the actin myofilaments. The troponin complex consists of three subunits: troponin C, troponin I, and troponin T. Troponin C specifically binds to calcium ions. When calcium binds to troponin C, it causes a conformational change in the troponin complex, which allows the myosin heads to bind to the exposed binding sites on the actin filaments. This interaction between actin and myosin is essential for muscle contraction. G-actin refers to the globular form of actin, which is the monomeric subunit that polymerizes to form the filamentous actin (F-actin).

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3. The part of the sarcomere that A (green) refers to is the _______________.

M line

A band

I band

Z disk

The correct answer is Z disk. The Z disk is a protein structure that anchors the thin filaments of the sarcomere and defines its boundaries. It is located in the middle of the I band and separates the sarcomere into two halves. The Z disk provides structural support and helps in the contraction and relaxation of the muscle fibers.

Explanation

The correct answer is Z disk. The Z disk is a protein structure that anchors the thin filaments of the sarcomere and defines its boundaries. It is located in the middle of the I band and separates the sarcomere into two halves. The Z disk provides structural support and helps in the contraction and relaxation of the muscle fibers.

4. During the depolarization phase of an action potential, the permeability of the plasma membrane to

Ca2+ increases

Na+ increases

K+ increases

Na+ decreases

During the depolarization phase of an action potential, the permeability of the plasma membrane to Na+ increases. This is because depolarization is the process in which the membrane potential becomes less negative or even positive, and it is mainly driven by the influx of Na+ ions into the cell. This increase in Na+ permeability allows more Na+ ions to enter the cell, leading to depolarization and the generation of an action potential.

Explanation

During the depolarization phase of an action potential, the permeability of the plasma membrane to Na+ increases. This is because depolarization is the process in which the membrane potential becomes less negative or even positive, and it is mainly driven by the influx of Na+ ions into the cell. This increase in Na+ permeability allows more Na+ ions to enter the cell, leading to depolarization and the generation of an action potential.

5. Which statement about muscles and muscle contraction is false?

ATP is required for the cycle of cross-bridge formation, movement, and release.

Muscle tissue shortens forcefully but lengthens passively.

The H zone contains only actin myofilaments

Type II muscle fibers respond rapidly to nervous stimulation.

The H zone contains both actin and myosin myofilaments, not only actin myofilaments.

Explanation

The H zone contains both actin and myosin myofilaments, not only actin myofilaments.

6. Of these, which is the greatest source of ATP?

Creatine kinase

Anaerobic respiration

Aerobic Respiration

Myokinase

How much ATP does each pathway produce?

Explanation

How much ATP does each pathway produce?

7. A weightlifter attempts to lift a weight from the floor, but the weight is so heavy that he is unable to move it. The type of muscle contraction the weightlifter is using is mostly

Concentric

Isometric

Isotonic

Isokinetic

The weightlifter is using isometric muscle contraction. Isometric contraction occurs when the muscle generates tension but does not change in length. In this case, the weightlifter is unable to move the heavy weight, so the muscles are contracting and generating tension, but there is no change in the length of the muscle fibers.

Explanation

The weightlifter is using isometric muscle contraction. Isometric contraction occurs when the muscle generates tension but does not change in length. In this case, the weightlifter is unable to move the heavy weight, so the muscles are contracting and generating tension, but there is no change in the length of the muscle fibers.

8. Given these events: 1) Calcium ions combine with tropomyosin 2) Calcium ions combine with troponin 3) Tropomyosin pulls away from actin 4) Troponin pulls away from actin 5) Tropomyosin pulls away from myosin 6) Troponin pulls away from myosin 7) Myosin binds to actin Choose the arrangement that lists the correct events in the order they occur in muscle contraction.

1, 4, 7

2, 5, 6

2, 3, 7

1, 3, 7

In muscle contraction, the correct sequence of events is as follows:
1) Calcium ions combine with troponin (event 2)
2) Tropomyosin pulls away from actin (event 3)
3) Myosin binds to actin (event 7)
Therefore, the correct arrangement is 2, 3, 7.

Explanation

In muscle contraction, the correct sequence of events is as follows:
1) Calcium ions combine with troponin (event 2)
2) Tropomyosin pulls away from actin (event 3)
3) Myosin binds to actin (event 7)
Therefore, the correct arrangement is 2, 3, 7.

9. Match the following

Sarcolemma

Sarcoplasm

Sarcoplasmic Reticulum

T Tubules

Tropomyosin

Neuromuscular Junction

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10. Given these structures: 1. Whole muscle 2. Muscle fibers 3. Myofilaments 4. Myofibrils 5. Muscle Fascicles Choose the correct order from largest to smallest.

1, 2, 5, 3, 4

1, 2, 5, 4, 3

1, 5, 2, 3, 4

1, 5, 2, 4, 3

The correct order from largest to smallest is 1, 5, 2, 4, 3. This is because the whole muscle is the largest structure, followed by muscle fascicles, muscle fibers, myofibrils, and finally myofilaments, which are the smallest structures.

Explanation

The correct order from largest to smallest is 1, 5, 2, 4, 3. This is because the whole muscle is the largest structure, followed by muscle fascicles, muscle fibers, myofibrils, and finally myofilaments, which are the smallest structures.

11. Match the following

Agonist

Antagonist

Synergists

Fixators

Prime Mover

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12. Given these events: (1) The sarcoplasm reticulum releases Ca+ (2) The sarcoplasm reticulum takes up Ca+ (3) Ca+ ions diffuse into the sarcoplasm (4) An AP moves down the T-tubule (5) The sarcomere shortens (6) The muscle relaxes Choose the arrangement that lists the events in the order they occur following a single stimulation.

1, 3, 4, 5, 2, 6

2, 3, 5, 4, 6, 1

4, 1, 3, 5, 2, 6

4, 2, 3, 5, 1, 6

The correct order of events following a single stimulation in muscle contraction is as follows: (1) An AP moves down the T-tubule, (2) The sarcoplasm reticulum releases Ca+, (3) Ca+ ions diffuse into the sarcoplasm, (4) The sarcomere shortens, (5) The sarcoplasm reticulum takes up Ca+, and (6) The muscle relaxes. This order ensures that the necessary calcium ions are present in the sarcoplasm for muscle contraction to occur, and then the calcium ions are removed to allow the muscle to relax.

Explanation

The correct order of events following a single stimulation in muscle contraction is as follows: (1) An AP moves down the T-tubule, (2) The sarcoplasm reticulum releases Ca+, (3) Ca+ ions diffuse into the sarcoplasm, (4) The sarcomere shortens, (5) The sarcoplasm reticulum takes up Ca+, and (6) The muscle relaxes. This order ensures that the necessary calcium ions are present in the sarcoplasm for muscle contraction to occur, and then the calcium ions are removed to allow the muscle to relax.

13. What are the main contributors of negative charges within a muscle cell?

Sodium Ions

Chloride Ions

Proteins

Potassium Ions

Proteins are the main contributors of negative charges within a muscle cell. Proteins contain negatively charged amino acids, which help to maintain the negative charge inside the cell. This negative charge is important for various cellular processes, including muscle contraction. Sodium ions, chloride ions, and potassium ions also play important roles in muscle cell function, but proteins are specifically responsible for the negative charges.

Explanation

Proteins are the main contributors of negative charges within a muscle cell. Proteins contain negatively charged amino acids, which help to maintain the negative charge inside the cell. This negative charge is important for various cellular processes, including muscle contraction. Sodium ions, chloride ions, and potassium ions also play important roles in muscle cell function, but proteins are specifically responsible for the negative charges.

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15. Factors that increase the number of cross-bridges and therefore increase the force of muscle contraction. (Multiple answers; select all that apply).

Larger muscle fiber diameter

Increased number of muscle fibers

More myofibrils

Frequency of stimulation

Muscle length at time of contraction

The factors that increase the number of cross-bridges and therefore increase the force of muscle contraction are larger muscle fiber diameter, more myofibrils, frequency of stimulation, and muscle length at the time of contraction. These factors contribute to a greater number of cross-bridges formed between the actin and myosin filaments, leading to a stronger muscle contraction.

Explanation

The factors that increase the number of cross-bridges and therefore increase the force of muscle contraction are larger muscle fiber diameter, more myofibrils, frequency of stimulation, and muscle length at the time of contraction. These factors contribute to a greater number of cross-bridges formed between the actin and myosin filaments, leading to a stronger muscle contraction.

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