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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Problem 8

Textbook Question

Order the following events of excitation and excitation-contraction coupling. Put 1 by the first event, 2 by the second, and so on.
The motor end plate generates an end-plate potential.
The action potential spreads along the T-tubules, SR Ca²⁺ channels are pulled open, and Ca²⁺ floods the cytosol.
Acetylcholine binds to receptors on the motor end plate, and ligand-gated ion channels open.
Ca²⁺ bind troponin, which allows tropomyosin to move away from the actin active site, initiating a contraction cycle.
The action potential propagates through the sarcolemma and dives deeply into the cell along the T-tubules.

Verified step by step guidance

Identify the sequence of events in excitation and excitation-contraction coupling by understanding the physiological process of muscle contraction.

Step 1: Acetylcholine (ACh) is released from the motor neuron and binds to receptors on the motor end plate, causing ligand-gated ion channels to open. This allows sodium ions (Na⁺) to enter the muscle fiber, initiating depolarization.

Step 2: The motor end plate generates an end-plate potential, which is a localized depolarization that triggers an action potential in the sarcolemma.

Step 3: The action potential propagates along the sarcolemma and dives deeply into the muscle fiber through the T-tubules, ensuring the signal reaches all parts of the muscle cell.

Step 4: The action potential in the T-tubules causes the sarcoplasmic reticulum (SR) to release calcium ions (Ca²⁺) into the cytosol by opening SR Ca²⁺ channels.

Step 5: Calcium ions bind to troponin, causing a conformational change that moves tropomyosin away from the actin active sites, allowing the myosin heads to bind to actin and initiate the contraction cycle.

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Key Concepts

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

Excitation-Contraction Coupling

Excitation-contraction coupling is the physiological process that links the electrical excitation of a muscle fiber to its contraction. It begins with the generation of an action potential in the muscle cell membrane, which then triggers the release of calcium ions from the sarcoplasmic reticulum. This increase in intracellular calcium concentration is crucial for muscle contraction, as it initiates the interaction between actin and myosin filaments.

Role of Acetylcholine

Acetylcholine is a neurotransmitter that plays a vital role in muscle contraction. It is released from motor neurons and binds to receptors on the motor end plate of the muscle fiber, leading to the opening of ligand-gated ion channels. This influx of sodium ions generates an end-plate potential, which is essential for initiating the action potential that propagates along the muscle membrane and into the T-tubules.

Calcium Ion Functionality

Calcium ions (Ca2+) are critical for muscle contraction. When the action potential reaches the T-tubules, it causes the sarcoplasmic reticulum to release Ca2+ into the cytosol. The binding of Ca2+ to troponin causes a conformational change that moves tropomyosin away from the actin active sites, allowing myosin heads to bind to actin and initiate the contraction cycle.

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Related Practice

Textbook Question

a. Describe the structure of a sarcomere and indicate the relationship of the sarcomere to myofilaments.

b. Explain the sliding filament model of contraction using appropriately labeled diagrams of a relaxed and a contracted sarcomere.

Explain how a slight (but smooth) contraction differs from a vigorous contraction of the same muscle. Use the concepts of multiple motor unit summation.

Muscle-relaxing drugs are administered to a patient during major surgery. Which of the two chemicals described next would be a good skeletal muscle relaxant and why?

• Chemical A binds to and blocks ACh receptors of muscle cells.

• Chemical B floods the muscle cells' cytoplasm with Ca²⁺.

What is the basic mechanism of contraction at the level of myofilaments?

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Textbook Question

Which of the following statements accurately describes the role of ATP in a muscle contraction?

a. ATP is directly responsible for the power stroke.