Ch. 10 Muscle Tissue and Physiology

Amerman3rd EditionHuman Anatomy & PhysiologyISBN: 9780138247201, 9780138247928, 9780138201814Not the one you use?Change textbook

Amerman 3rd Edition

Ch. 10 Muscle Tissue and Physiology

Problem 8

Chapter 10, Problem 8

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

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

a. ATP is directly responsible for the power stroke.

b. ATP moves troponin and tropomyosin away from actin.

c. ATP breaks the actin/myosin attachment and 'cocks' the myosin head.

d. ATP causes the myofilaments to shorten.

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Textbook Question

Which of the following energy sources would provide the majority of the ATP for a person running a 26-mile marathon?

a. Stored ATP

b. Glycolytic catabolism

c. Oxidative catabolism

d. Creatine phosphate

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Textbook Question

Mr. Nasheed has cerebral palsy and suffers severe skeletal muscle spasms as a result of his condition. He is prescribed the drug dantrolene, which prevents the release of Ca²⁺ from the SR. Explain how this will treat his muscle spasms.

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Textbook Question

A muscle fiber relaxes when:

a. The concentration of Ca²⁺ in the cytosol returns to resting levels.

b. The supply of ATP is exhausted.

c. Ca²⁺ flood the cytosol.

d. Acetylcholine is released from the axon terminal and the sarcolemma depolarizes.

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Textbook Question

Match the following terms with the correct definition.

____Z-disc

____Sarcomere