Question at position 3 Which structural feature enables the rapid propagation of the action potential deep within the muscle fiber?Z-discsTransverse tubules (T-tubules)Sarcoplasmic reticulum cisternaeM-linesClear my selectionSingle choice
A
Z-discs
B
Transverse tubules (T-tubules)
C
Sarcoplasmic reticulum cisternae
D
M-lines

Question

Question at position 3 Which structural feature enables the rapid propagation of the action potential deep within the muscle fiber?Z-discsTransverse tubules (T-tubules)Sarcoplasmic reticulum cisternaeM-linesClear my selectionSingle choice

A

Z-discs

B

Transverse tubules (T-tubules)

C

Sarcoplasmic reticulum cisternae

D

M-lines

BlackTom AI · Accepted Answer

Transverse tubules (T-tubules) are invaginations of the sarcolemma that transmit the action potential into the fiber’s interior, so they enable rapid propagation of the action potential deep within the muscle fiber.

1) Relevant knowledge points and concepts
- Sarcolemma: the muscle cell membrane that conducts action potentials on the cell surface.
- T-tubules: deep invaginations of the sarcolemma that penetrate the myofiber and conduct electrical signals inward.
- Sarcoplasmic reticulum (SR) and terminal cisternae: intracellular Ca2+ store that releases Ca2+ in response to signals; forms triads with T-tubules in skeletal muscle.
- Excitation–contraction coupling: depolarization → DHP (voltage-sensing) receptors in T-tubules activate ryanodine receptors on SR → Ca2+ release → contraction.

2) Step-by-step reasoning
- An action potential begins on the sarcolemma and must reach the entire volume of a large muscle fiber to produce coordinated contraction.
- T-tubules are continuous with the sarcolemma, so the electrical depolarization travels down these tubules as if they were extensions of the membrane.
- In the interior, T-tubules are physically adjacent to SR terminal cisternae (forming triads), allowing voltage sensors (DHP receptors) in T-tubules to trigger SR Ca2+ release quickly and uniformly throughout the fiber.
- Thus T-tubules are the structural feature that conducts the AP inward, ensuring synchronous Ca2+ release and rapid contraction.

3) Intermediate steps/calculations
- No numeric calculation is required. Mechanistic steps: sarcolemma AP → T-tubule conduction → DHP activation → ryanodine receptor opening → SR Ca2+ release.

4) Why the correct answer is correct
- Only T-tubules are specialized membrane invaginations whose purpose is to carry electrical signals into the fiber’s core and coordinate rapid, deep propagation of the action potential for excitation–contraction coupling.

5) Why other options are incorrect
- Z-discs: structural boundaries anchoring actin filaments; do not conduct APs.
- Sarcoplasmic reticulum cisternae: store and release Ca2+, but they do not propagate action potentials inward.
- M-lines: central structural support for myosin filaments in the sarcomere; not involved in electrical conduction.

6) Conclusion
- Therefore the correct answer is Transverse tubules (T-tubules), which matches the provided answer.

Question at position 3 Which structural feature enables the rapid propagation of the action potential deep within the muscle fiber?Z-discsTransverse tubules (T-tubules)Sarcoplasmic reticulum cisternaeM-linesClear my selectionSingle choice

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Question at position 3 Which structural feature enables the rapid propagation of the action potential deep within the muscle fiber?Z-discsTransverse tubules (T-tubules)Sarcoplasmic reticulum cisternaeM-linesClear my selectionSingle choice

Similar Questions

Question at position 7 The major function of the sarcoplasmic reticulum in skeletal muscle contraction is to: provide a source of myosin for the contraction processstore ATPregulate intracellular calcium concentrationsynthesize actin and myosin myofilaments

Muscle cramps are defined as sudden, painful ________blank of a muscle or group of muscles.

Antagonists muscle group: A to B: EJ __extenders __ B to A: EJ __ extenders __ Antagonists are passively __ lengthening __ from A to B and passively __shortening __ from B to A.

Question1.20 Which of the following does NOT directly impact force production potential of a muscle? Muscle volume Muscle fibre type Neural recruitment frequency Muscle fibre Pinnation Muscle length ResetMaximum marks: 1 Flag question undefined

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