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Questions and Answers
What is the primary function of the sarcoplasm in skeletal muscle fibers?
Which of the following is NOT a characteristic of skeletal muscle?
What is the primary function of the transverse tubules (T-tubules) in skeletal muscle fibers?
What is the purpose of the extensive vascular system in skeletal muscle?
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What is the role of the sarcoplasmic reticulum (SR) in skeletal muscle fibers?
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Which of the following is a characteristic of skeletal muscle fibers?
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What is the purpose of the connective tissue (epimysium, perimysium, endomysium) in skeletal muscle?
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What is the role of the sarcolemma in skeletal muscle fibers?
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In the T-tubule membrane, what is the function of DHPR?
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What is the primary function of Troponin-C?
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What is the main component of thick fibers in myofibrils?
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What is the function of Nebulin in myofibrils?
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What is the structure formed by a transverse tubule flanked by two terminal cisternae?
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What is the function of Tropomyosin in resting muscle cells?
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What is the binding site for actin in myofibrils?
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What is the function of Titin in myofibrils?
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Study Notes
Muscle Structure and Function
- A/I bands and H zones are fused together in skeletal muscle.
- DHPR (Dihydropyridine receptor) is a voltage-gated sensor in the T-tubule membrane.
- RYR (Ryanodine Receptor) is a Ca2+ release channel in the SR membrane.
Muscle Fiber Components
- Myofibrils: site of contraction, consisting of thick and thin filaments.
- Thick filaments: • Made up of myosin, composed of 2 heavy chains and 4 light chains. • Heavy chain is the motor domain for binding ATP and releasing to create movement.
- Thin filaments: • Actin: a globular protein that polymerizes to form F-actin filaments. • Tropomyosin: a strand protein wrapped spirally around F-actin filaments. • Troponin: a complex of 3 subunits (T, I, and C) that regulate muscle contraction.
Troponin and Muscle Contraction
- Troponin-C binds to 4 Ca2+ ions, initiating muscle contraction.
- In the absence of Ca2+, tropomyosin inhibits myosin head attachment to actin, preventing contraction.
- When Ca2+ binds to troponin, the complex shifts, allowing myosin heads to bind to actin and initiate contraction.
Skeletal Muscle Characteristics
- Contract in response to signals from somatic motor neurons.
- Cannot initiate their own contraction.
- Functions: movement, maintaining posture, supporting soft tissue, and storing nutrient reserves.
Skeletal Muscle Structure
- Consists of muscle fibers developed from myoblasts.
- Surrounded by connective tissue (epimysium, perimysium, and endomysium).
- Nerves: controlled by somatic nervous system, with each fiber supplied with nerve endings that control contraction.
- Blood vessels: extensive vascular system supplies oxygen and nutrients and removes waste.
Muscle Fiber Components
- Sarcolemma: maintains transmembrane potential.
- Sarcoplasm: rich in glycogen and myoglobin, providing ATP for muscle contraction.
- Myofibrils and sarcoplasmic reticulum (SR): site of muscle contraction and Ca2+ storage.
Transverse Tubules (T-Tubules) and Sarcoplasmic Reticulum (SR)
- T-tubules: passageways from extracellular space to terminal cisternae of SR, allowing nerve message and nutrient passage.
- SR: stores Ca2+ at rest, releasing it upon stimulation, and pumping it back in the absence of stimulation.
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Description
Test your knowledge on the basics of skeletal muscles, including their characteristics, functions, and mechanisms of contraction.
