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Questions and Answers
What is the primary role of troponin in muscle contraction?
What is the primary role of troponin in muscle contraction?
Which event is essential for the excitation-contraction coupling in skeletal muscle?
Which event is essential for the excitation-contraction coupling in skeletal muscle?
What happens during muscle relaxation?
What happens during muscle relaxation?
In isotonic contractions, what happens to the muscle?
In isotonic contractions, what happens to the muscle?
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Which statement describes isometric contractions?
Which statement describes isometric contractions?
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What initiates the release of acetylcholine from synaptic vesicles at the neuromuscular junction?
What initiates the release of acetylcholine from synaptic vesicles at the neuromuscular junction?
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What happens to acetylcholine after it binds to the ligand-gated sodium channels?
What happens to acetylcholine after it binds to the ligand-gated sodium channels?
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Which component of actin myofilaments covers the active sites on G actin subunits in relaxed muscle?
Which component of actin myofilaments covers the active sites on G actin subunits in relaxed muscle?
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What role does acetylcholinesterase play at the neuromuscular junction?
What role does acetylcholinesterase play at the neuromuscular junction?
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Which process is involved in the reformation of acetylcholine within the presynaptic terminal?
Which process is involved in the reformation of acetylcholine within the presynaptic terminal?
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What is a physiological change that occurs with aging in the muscular system?
What is a physiological change that occurs with aging in the muscular system?
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What is a primary cause of muscle cramps?
What is a primary cause of muscle cramps?
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Which condition is characterized by chronic widespread pain in skeletal muscles?
Which condition is characterized by chronic widespread pain in skeletal muscles?
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What diagnostic method is used for confirming Myasthenia Gravis?
What diagnostic method is used for confirming Myasthenia Gravis?
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What type of muscular issue often follows vigorous exercise?
What type of muscular issue often follows vigorous exercise?
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Which of the following is NOT a common mechanism involved in muscle fatigue?
Which of the following is NOT a common mechanism involved in muscle fatigue?
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What genetic mutation is associated with Duchenne Muscular Dystrophy?
What genetic mutation is associated with Duchenne Muscular Dystrophy?
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What is a primary cause of tendinitis in skeletal muscles?
What is a primary cause of tendinitis in skeletal muscles?
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What is the primary role of the neuromuscular junction in muscle physiology?
What is the primary role of the neuromuscular junction in muscle physiology?
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Which component of the neuromuscular junction contains acetylcholine receptors?
Which component of the neuromuscular junction contains acetylcholine receptors?
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What occurs first during the process of muscle contraction at the neuromuscular junction?
What occurs first during the process of muscle contraction at the neuromuscular junction?
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What happens at the presynaptic membrane when an action potential arrives?
What happens at the presynaptic membrane when an action potential arrives?
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Which structure separates the axonal endings and the muscle fibers at the neuromuscular junction?
Which structure separates the axonal endings and the muscle fibers at the neuromuscular junction?
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What is the function of synaptic vesicles in the neuromuscular junction?
What is the function of synaptic vesicles in the neuromuscular junction?
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In the context of muscle physiology, what does the term 'action potential' refer to?
In the context of muscle physiology, what does the term 'action potential' refer to?
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Which of the following is NOT a component of the neuromuscular junction?
Which of the following is NOT a component of the neuromuscular junction?
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Which statement correctly describes the action of myosin during muscle contraction?
Which statement correctly describes the action of myosin during muscle contraction?
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What is the primary function of the T tubule within skeletal muscle fibers?
What is the primary function of the T tubule within skeletal muscle fibers?
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In which type of muscle contraction is the muscle unable to visibly shorten despite exerting force?
In which type of muscle contraction is the muscle unable to visibly shorten despite exerting force?
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Which event occurs first during muscle contraction activation?
Which event occurs first during muscle contraction activation?
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What is the role of tropomyosin in muscle contraction?
What is the role of tropomyosin in muscle contraction?
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Which structure is primarily responsible for calcium ion storage in muscle cells?
Which structure is primarily responsible for calcium ion storage in muscle cells?
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What happens to tropomyosin in response to calcium ion binding?
What happens to tropomyosin in response to calcium ion binding?
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Which statement about the myosin head during contraction is incorrect?
Which statement about the myosin head during contraction is incorrect?
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Study Notes
Neuromuscular Junction
- Stimulation of muscle cell by a nerve happens at a neuromuscular junction.
- The neuromuscular junction is formed from axonal endings and motor end plate.
- Axonal endings have small membranous sacs called synaptic vesicles containing acetylcholine.
- Motor end plate is the muscle plasma membrane in the area of the junction, and contains acetylcholine receptors.
- Axonal endings and muscle fibers are separated by a space called the synaptic cleft.
Muscle Contraction
- The process of muscle contraction begins when an action potential arrives at the presynaptic terminal.
- Voltage gated calcium channels in the presynaptic membrane open.
- Acetylcholine is then released into the synaptic cleft by exocytosis.
- Acetylcholine binds to ligand-gated sodium channels on the motor end plate.
- Ligand-gated sodium channels open and sodium enters the muscle fiber. An action potential is generated if depolarization passes threshold.
- Acetylcholine unbinds from the ligand-gated channels, which then close.
- Acetylcholinesterase removes acetylcholine from the synaptic cleft.
- Choline is symported with sodium in the presynaptic terminal.
- Acetylcholine is reformed within the presynaptic terminal.
Actin and Myosin Myofilament Structure
- Actin Myofilament Component: Globular (G) actin forms a strand called fibrous (F) actin. Tropomyosin covers the active sites on the G actin subunits in relaxed muscle. Troponin anchors to the actin, and binds calcium.
- Myosin Myofilament Component: Myosin molecules consist of two myosin heavy chains and two myosin heads which bind to active sites on actin molecules to form cross bridges.
Excitation-Contraction Coupling
- Excitation-contraction coupling occurs at the triad, which links the electrical component of muscle contraction to the mechanical component.
- A skeletal muscle must be stimulated by a nerve ending, propagate an action potential along its sarcolemma, and have a rise in intracellular calcium levels in order to contract.
- Calcium release from the sarcoplasmic reticulum is triggered by the action potential traveling down the T tubules, activating voltage-sensitive receptors that open calcium release channels.
Cross-bridge Movement
- Calcium ions bind to troponin, causing tropomyosin to move away from the active sites on actin.
- Myosin heads bind to the exposed active sites on actin, forming cross-bridges.
- The myosin heads pivot, pulling the thin filaments past the thick filaments. This is powered by ATP hydrolysis.
- The myosin heads detach from actin, then bind to a new active site further down the actin filament, repeating the cycle.
Types of Muscle Contractions
- Isometric contractions occur when the muscle does not shorten, but tension increases.
- Isotonic contractions occur when the muscle shortens and tone remains constant throughout the contraction.
- Concentric contractions occur when the muscle shortens to move a load.
- Eccentric contractions occur when the muscle lengthens while resisting a load.
Disorders of the Muscular System
- Aging: Physiologic muscle atrophy is a age-related reduction in muscle mass and regulation of muscle function. Loss of muscle fibers begins as early as 25 years old.
- Muscle fatigue: This is a temporary state of reduced work capacity due to factors such as acidosis, ATP depletion, oxidative stress and local inflammatory response.
- Muscle soreness: Caused by inflammatory chemical influx into the muscle fibers.
- Cramps: Painful spastic contractions of skeletal muscle, caused by dehydration or ion imbalance.
- Tendonitis: Inflammation of a tendon or its attachment point due to overuse.
- Fibromyalgia: Non-life-threatening chronic widespread pain in skeletal muscles with no known cure.
- Myasthenia gravis: Autoimmune disease in which autoantibodies bind to acetylcholine receptors at the neuromuscular junction.
- Duchenne muscular dystrophy: Mutations in the dystrophin gene on the x chromosome causing progressive muscle weakness and muscle contractures.
Diagnostic Tests for Muscular System Disorders
- Electromyography: Measures electrical activity of muscles.
- Muscle biopsies: Are used to examine muscle tissue structure.
- Immunohistochemical studies: Detect specific proteins or antibodies in muscle tissue.
- Serum creatinine: Measures the level of creatinine in the blood, which can be elevated in muscle damage or disease.
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Description
Explore the intricate processes involved in muscle contraction and the critical role of the neuromuscular junction. This quiz covers how nerve stimulation leads to muscle action and the functions of synaptic vesicles and acetylcholine. Test your knowledge on the mechanisms of action potentials and synaptic transmission.
