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Questions and Answers
What is the primary function of calmodulin in smooth muscle contraction?
What is the primary function of calmodulin in smooth muscle contraction?
What characterizes malignant hyperthermia?
What characterizes malignant hyperthermia?
Which type of channels are involved in calcium entry for smooth muscle contraction?
Which type of channels are involved in calcium entry for smooth muscle contraction?
How do cardiac muscle cells effectively communicate with one another?
How do cardiac muscle cells effectively communicate with one another?
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What distinguishes the T tubules in cardiac muscles from those in skeletal muscles?
What distinguishes the T tubules in cardiac muscles from those in skeletal muscles?
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What initiates the contraction of a muscle cell during excitation-contraction coupling?
What initiates the contraction of a muscle cell during excitation-contraction coupling?
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What structure is responsible for transmitting the action potential deep into the muscle fiber?
What structure is responsible for transmitting the action potential deep into the muscle fiber?
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Which process follows the depolarization of the T-tubule membrane?
Which process follows the depolarization of the T-tubule membrane?
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What is the role of sodium ions during the excitation phase of muscle contraction?
What is the role of sodium ions during the excitation phase of muscle contraction?
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How does excitation-contraction coupling primarily link excitation to contraction?
How does excitation-contraction coupling primarily link excitation to contraction?
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What anatomical feature facilitates the connection between the T-tubule and the sarcoplasmic reticulum?
What anatomical feature facilitates the connection between the T-tubule and the sarcoplasmic reticulum?
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What happens during muscle fiber relaxation?
What happens during muscle fiber relaxation?
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Which type of muscle is characterized by a different mechanism of excitation-contraction coupling compared to skeletal muscle?
Which type of muscle is characterized by a different mechanism of excitation-contraction coupling compared to skeletal muscle?
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What does the DHPR (dihydropyridine receptor) primarily function as in muscle contraction?
What does the DHPR (dihydropyridine receptor) primarily function as in muscle contraction?
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What triggers the release of calcium ions during muscle contraction?
What triggers the release of calcium ions during muscle contraction?
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What role does troponin C play in muscle contraction?
What role does troponin C play in muscle contraction?
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What effect does the calcium-troponin complex have on the tropomyosin protein?
What effect does the calcium-troponin complex have on the tropomyosin protein?
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What process occurs to shorten the sarcomere during muscle contraction?
What process occurs to shorten the sarcomere during muscle contraction?
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Which pump is responsible for muscle relaxation by moving calcium back into the sarcoplasmic reticulum?
Which pump is responsible for muscle relaxation by moving calcium back into the sarcoplasmic reticulum?
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In an excited muscle, how does the presence of calcium ions in the cytosol affect muscle contraction?
In an excited muscle, how does the presence of calcium ions in the cytosol affect muscle contraction?
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What is the condition of calcium levels in the cytosol during a resting muscle state?
What is the condition of calcium levels in the cytosol during a resting muscle state?
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Study Notes
Excitation-Contraction Coupling (EC Coupling)
- EC coupling is the link between muscle excitation and muscle contraction.
- Action potentials trigger muscle cell contraction.
- Calcium ions control whether or not contraction occurs.
- The link between muscle excitation and calcium release is excitation-contraction coupling.
Objectives
- Understand EC coupling.
- Understand the passage of impulses.
- Understand the function of T-tubules.
- Understand how calcium is released.
- Know the muscle contraction sequence.
- Understand muscle relaxation.
- Compare smooth and cardiac muscle differences.
- Understand applied aspects of EC coupling.
What is EC Coupling?
- Action potentials initiate muscle contraction.
- Calcium regulates contraction.
- Excitation-contraction coupling links muscle excitation to calcium release from the sarcoplasmic reticulum.
The Passage of the Impulse
- Nerve impulses travel to the post-synaptic membrane via neuromuscular junctions.
- Conformational changes result in sodium ion influx into muscle fibers.
- Sodium accumulation depolarizes the membrane, creating an end-plate potential.
- The potential increases towards the action potential threshold.
The T-tubule
- T-tubules are invaginations of the sarcolemma that extend into the muscle fiber.
- T-tubule lumen is continuous with the extracellular fluid (ECF).
- Depolarization during action potentials occurs across the T-tubule membrane.
- Terminal cisterns, swellings of sarcoplasmic reticulum (SR), are on each side of T-tubules.
How Depolarization Opens a Calcium Channel
- Dihydropyridine receptor (DHPR) is a voltage sensor in the T-tubule membrane.
- DHPR is closely associated with the foot of the calcium channel.
- The action potential passes to the L-tubules, containing the ryanodine receptor (RyR).
- The voltage sensor changes shape when depolarized, causing the RyR to open, releasing calcium.
The Contraction Sequence
- Accumulated calcium initiates and maintains sarcomere contraction.
- Free calcium binds to troponin C on thin actin filaments.
- This forms the active calcium-troponin complex.
Binding of Calcium to Troponin C
- Calcium binds to troponin C.
- This causes a conformational change in tropomyosin.
- This exposes myosin binding sites on actin filaments.
Myosin Head Binding
- Myosin heads bind to actin.
- ADP and IP release trigger power strokes, shortening sarcomeres.
Relaxation
- SERCA pump (Sarcoplasmic/Endoplasmic Reticulum Calcium ATPase pump) actively pumps calcium back into the sarcoplasmic reticulum.
Differences in Smooth Muscles
- Different calcium channels (voltage-gated, ligand-gated, second messenger-gated, or mechanically-gated) exist depending on smooth muscle type.
- Calcium can enter from the extracellular fluid.
- IP3 (inositol triphosphate) is a second messenger that opens channels and releases calcium from the SR.
- Calcium binds to calmodulin.
- Myosin light chain kinase (MLCK) activates the myosin head through phosphorylation.
Differences in Cardiac Muscles
- Cardiac muscle cells form a syncytium (electrically connected).
- Gap junctions, made of connexins, link cells.
- T-tubules are well-developed.
- Only one terminal cistern per T-tubule (a diad).
Applied Aspects (e.g., Malignant Hyperthermia)
- Malignant hyperthermia is caused by RyR mutations in L-tubules.
- Symptoms include increased body temperature, muscle contractions, rigidity, and heart rate with high fever.
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Description
Explore the intricate process of excitation-contraction coupling, where electrical impulses lead to muscle contraction. This quiz covers essential concepts such as the function of T-tubules, calcium release, and differences between muscle types. Enhance your understanding of how muscle contraction and relaxation occur through this vital physiological mechanism.