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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3:16 minutes

Problem 23

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.

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Step 1: Define the sarcomere structure. A sarcomere is the functional unit of a muscle fiber, located between two Z-discs. It consists of thick filaments (myosin) and thin filaments (actin), which are organized in a specific pattern. The sarcomere includes the A-band (region containing the entire length of thick filaments), the I-band (region containing only thin filaments), the H-zone (center of the A-band where there are only thick filaments), and the M-line (center of the sarcomere where thick filaments are anchored).

Step 2: Explain the relationship between sarcomeres and myofilaments. Myofilaments are the protein filaments (actin and myosin) that make up the sarcomere. The thick filaments (myosin) are anchored at the M-line, while the thin filaments (actin) are anchored at the Z-discs. The arrangement of these filaments within the sarcomere allows for muscle contraction through their interaction.

Step 3: Introduce the sliding filament model of contraction. This model explains how muscle contraction occurs at the molecular level. During contraction, the thin filaments slide past the thick filaments, shortening the sarcomere and thus the muscle fiber. This sliding is powered by the interaction between actin and myosin, facilitated by ATP and calcium ions.

Step 4: Describe the relaxed sarcomere. In a relaxed state, the sarcomere is at its maximum length, with the H-zone and I-band clearly visible. The thick and thin filaments overlap minimally, and the Z-discs are farther apart.

Step 5: Describe the contracted sarcomere. In a contracted state, the sarcomere shortens as the thin filaments slide toward the M-line, overlapping more with the thick filaments. The H-zone disappears, the I-band narrows, and the Z-discs move closer together. Label diagrams to show these changes, highlighting the movement of filaments and the reduction in sarcomere length.

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Key Concepts

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

Sarcomere Structure

A sarcomere is the fundamental unit of muscle contraction, composed of thick and thin myofilaments. The thick filaments are primarily made of myosin, while the thin filaments consist mainly of actin, along with troponin and tropomyosin. Sarcomeres are organized in a repeating pattern along the length of myofibrils, separated by Z-discs, which anchor the thin filaments and define the boundaries of each sarcomere.

Myofilaments

Myofilaments are the contractile proteins within the sarcomere, categorized into thick and thin filaments. Thick filaments, composed of myosin, have heads that interact with the actin of thin filaments during contraction. Thin filaments, primarily made of actin, provide the site for myosin binding, and their arrangement and interaction are crucial for muscle contraction and relaxation.

Sliding Filament Model

The sliding filament model explains how muscle contraction occurs at the molecular level. According to this model, during contraction, the myosin heads attach to actin filaments, pulling them inward and causing the sarcomere to shorten. This process is powered by ATP and results in the sliding of thin filaments over thick filaments, leading to muscle shortening and force generation.

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Related Practice

Textbook Question

Aerobic exercise results in all of the following except:

a. More capillaries surrounding muscle fibers

b. More mitochondria in muscle cells

c. Increased size and strength of existing muscle cells

d. More myoglobin

What is the importance of acetylcholinesterase in muscle cell contraction?

Explain what is meant by the term excitation-contraction coupling.

Define and draw a motor unit.

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

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.

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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.

Key Concepts

Sarcomere Structure

Myofilaments

Sliding Filament Model

Watch next

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.