Table of contents

1. Introduction to Anatomy & Physiology5h 43m
2. Cell Chemistry & Cell Components12h 36m
3. Energy & Cell Processes10h 6m
4. Tissues & Histology10h 3m
5. Integumentary System2h 20m
6. Bones & Skeletal Tissue2h 16m
7. The Skeletal System2h 35m
8. Joints2h 17m
9. Muscle Tissue2h 33m
10. Muscles1h 11m
11. Nervous Tissue and Nervous System1h 35m
12. The Central Nervous System1h 6m
- Introduction to the Central Nervous System
  18m
- The Cerebrum
  48m
13. The Peripheral Nervous System1h 26m
14. The Autonomic Nervous System1h 38m
15. The Special Senses2h 41m
16. The Endocrine System2h 48m
17. The Blood3h 22m
18. The Heart3h 42m
19. The Blood Vessels3h 35m
20. The Lymphatic System3h 16m
21. The Immune System14h 37m
22. The Respiratory System3h 20m
23. The Digestive System2h 5m
24. Metabolism and Nutrition4h 0m
25. The Urinary System2h 39m
26. Fluid and Electrolyte Balance, Acid Base Balance37m
27. The Reproductive System2h 5m
28. Human Development1h 21m
29. Heredity3h 32m

9. Muscle Tissue

Steps of Muscle Contraction

Anatomy & Physiology

9. Muscle Tissue

Steps of Muscle Contraction

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3:19 minutes

Problem 22

Textbook Question

For each portion of a myogram tracing a twitch in a stimulated calf muscle fiber, describe the events that occur within the muscle fiber.

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Identify the three main phases of a muscle twitch as shown in the myogram: the latent period, the contraction phase, and the relaxation phase.

During the latent period, explain that the muscle fiber is stimulated by the motor neuron, leading to the release of acetylcholine at the neuromuscular junction. This triggers an action potential that travels along the sarcolemma and into the T-tubules, causing calcium ions to be released from the sarcoplasmic reticulum.

In the contraction phase, describe how calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the active sites on actin. This allows myosin heads to bind to actin, forming cross-bridges, and initiating the sliding filament mechanism, which generates tension in the muscle fiber.

During the relaxation phase, explain that calcium ions are actively pumped back into the sarcoplasmic reticulum, reducing their concentration in the cytoplasm. This causes troponin to return to its original shape, allowing tropomyosin to cover the active sites on actin, thereby ending cross-bridge formation.

Conclude by noting that the muscle fiber returns to its resting state, and the tension in the muscle decreases, completing the twitch cycle as shown in the myogram tracing.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Muscle Contraction Mechanism

Muscle contraction occurs through a process called the sliding filament theory, where actin and myosin filaments within the muscle fibers slide past each other. This process is initiated by the release of calcium ions from the sarcoplasmic reticulum, which binds to troponin, causing a conformational change that allows myosin heads to attach to actin and pull, resulting in contraction.

Myogram Phases

A myogram tracing of a muscle twitch consists of three distinct phases: the latent period, contraction phase, and relaxation phase. The latent period is the time between stimulation and the onset of contraction, during which the muscle prepares for contraction. The contraction phase is when the muscle fibers actively shorten, and the relaxation phase is when the muscle returns to its resting state as calcium is reabsorbed.

Neuromuscular Junction

The neuromuscular junction is the synapse between a motor neuron and a muscle fiber, where the transmission of signals occurs. When a nerve impulse reaches the junction, acetylcholine is released, binding to receptors on the muscle fiber's membrane, leading to depolarization and the initiation of an action potential that triggers muscle contraction.

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Textbook Question

Chemical A binds and blocks acetylcholine receptors of muscle cells. Chemical B floods the cytoplasm of muscle cells with calcium ions. Which chemical would make the best muscle relaxant, and why?

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Textbook Question

What structural feature of a skeletal muscle fiber propagates action potentials into the interior of the cell?

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Textbook Question

What forms of energy reserves do resting skeletal muscle fibers contain?

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Textbook Question

Areas of the body where you would not expect to find slow fibers include the

(a) Back and calf muscles

(b) Eye and hand

(d) All of these

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Textbook Question

Characteristics of isometric contractions include all but:

a. Shortening

b. Increased muscle tension throughout the contraction phase

c. Absence of shortening

d. Used in resistance training

When a suicide victim was found, the coroner was unable to remove the drug vial clutched in his hand. Explain the reasons for this. If the victim had been discovered three days later, would the coroner have had the same difficulty? Explain.

Define neuromuscular junction, motor unit, tetanus, graded response, aerobic respiration, anaerobic glycolysis, muscle fatigue, and neurotransmitter.

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Textbook Question

When Eric returned from jogging, he was breathing heavily and sweating profusely, and he complained that his legs ached and felt weak. On the basis of what you have learned about muscle energy metabolism, respond to the following questions:

a. Why is Eric breathing heavily?

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