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Questions and Answers
What percentage of total body weight do skeletal muscles typically make up in males?
What percentage of total body weight do skeletal muscles typically make up in males?
About 40%.
Define contractility in relation to muscle properties.
Define contractility in relation to muscle properties.
Contractility is the ability of a muscle to shorten with force.
What is the capacity of a muscle to respond to a stimulus called?
What is the capacity of a muscle to respond to a stimulus called?
Excitability.
Explain the importance of extensibility in muscle function.
Explain the importance of extensibility in muscle function.
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What does the elasticity property of muscles indicate?
What does the elasticity property of muscles indicate?
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What type of muscle is characterized as voluntary and can be consciously controlled?
What type of muscle is characterized as voluntary and can be consciously controlled?
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List one example of involuntary muscle action.
List one example of involuntary muscle action.
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What are the primary functions served by muscle tissues?
What are the primary functions served by muscle tissues?
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What causes the shortening of myofibrils during muscle contraction?
What causes the shortening of myofibrils during muscle contraction?
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How do myosin cross bridges contribute to muscle contraction?
How do myosin cross bridges contribute to muscle contraction?
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What changes occur to the A and I bands during muscle contraction?
What changes occur to the A and I bands during muscle contraction?
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What is the role of the neuromuscular junction in muscle contraction?
What is the role of the neuromuscular junction in muscle contraction?
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How does the action potential propagate along the sarcolemma and into the muscle fiber?
How does the action potential propagate along the sarcolemma and into the muscle fiber?
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What effect does the release of acetylcholine (ACh) have at the neuromuscular junction?
What effect does the release of acetylcholine (ACh) have at the neuromuscular junction?
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What is the relationship between T tubules and the sarcoplasmic reticulum (SR) during excitation-contraction coupling?
What is the relationship between T tubules and the sarcoplasmic reticulum (SR) during excitation-contraction coupling?
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What phenomenon is described when APs in T tubules result in Ca2+ release from the sarcoplasmic reticulum?
What phenomenon is described when APs in T tubules result in Ca2+ release from the sarcoplasmic reticulum?
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Why do H bands shorten during muscle contraction?
Why do H bands shorten during muscle contraction?
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What retains its length during muscle contraction, and why is this significant?
What retains its length during muscle contraction, and why is this significant?
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What happens to calcium ions during muscle relaxation?
What happens to calcium ions during muscle relaxation?
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Define a motor unit and its components.
Define a motor unit and its components.
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How does the number of muscle fibers in a motor unit affect muscle control?
How does the number of muscle fibers in a motor unit affect muscle control?
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What is the role of motor unit recruitment in muscle contraction strength?
What is the role of motor unit recruitment in muscle contraction strength?
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What occurs when a motor neuron is activated?
What occurs when a motor neuron is activated?
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Give an example of a muscle with a high density of motor units and its significance.
Give an example of a muscle with a high density of motor units and its significance.
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Contrast the structure of motor units in fine control muscles versus larger muscles.
Contrast the structure of motor units in fine control muscles versus larger muscles.
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What is the significance of Ca2+ binding to troponin C during muscle contraction?
What is the significance of Ca2+ binding to troponin C during muscle contraction?
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What happens when action potentials cease in muscle fibers?
What happens when action potentials cease in muscle fibers?
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Explain the trade-off between muscle control and strength.
Explain the trade-off between muscle control and strength.
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What is muscle tone and how is it established?
What is muscle tone and how is it established?
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Differentiate between hypotonia and hypertonia.
Differentiate between hypotonia and hypertonia.
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What are the differences between isometric and isotonic contractions?
What are the differences between isometric and isotonic contractions?
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Describe the characteristics of Type I muscle fibers.
Describe the characteristics of Type I muscle fibers.
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What is the role of satellite cells in skeletal muscle repair?
What is the role of satellite cells in skeletal muscle repair?
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How do Type II A fibers differ from Type IIX fibers?
How do Type II A fibers differ from Type IIX fibers?
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What is the significance of the alternating activation of motor units?
What is the significance of the alternating activation of motor units?
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What type of muscle tissue is striated and can be both voluntary and involuntary?
What type of muscle tissue is striated and can be both voluntary and involuntary?
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What role does the autonomic nervous system play in muscle function?
What role does the autonomic nervous system play in muscle function?
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What is the primary structural unit of a muscle fiber?
What is the primary structural unit of a muscle fiber?
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What is the connective tissue that surrounds individual muscle fibers called?
What is the connective tissue that surrounds individual muscle fibers called?
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What features distinguish cardiac muscle from smooth muscle?
What features distinguish cardiac muscle from smooth muscle?
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What is the function of the sarcoplasmic reticulum in muscle fibers?
What is the function of the sarcoplasmic reticulum in muscle fibers?
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What distinguishes smooth muscle in terms of its cellular structure?
What distinguishes smooth muscle in terms of its cellular structure?
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What is the collective term for the connective tissue that encases a muscle and its fascicles?
What is the collective term for the connective tissue that encases a muscle and its fascicles?
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What is the smallest functional unit of a muscle that can contract?
What is the smallest functional unit of a muscle that can contract?
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How does skeletal muscle achieve its striated appearance?
How does skeletal muscle achieve its striated appearance?
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Study Notes
Muscular System Overview
- Muscle tissue is one of four basic tissue types.
- Skeletal muscles make up a significant portion of body weight (40% in males, 32% in females).
- Muscle tissues perform various functions.
Muscle Tissue Properties
- Contractility: Ability of a muscle to shorten with force.
- Excitability: Capacity of muscle to respond to a stimulus.
- Extensibility: Ability of muscle to be stretched to its normal resting length and beyond.
- Elasticity: Ability of muscle to recoil to its original resting length after stretched.
Muscle Classification
- Voluntary Muscles: Controlled by conscious thought (skeletal muscles).
- Involuntary Muscles: Not under conscious control (cardiac and smooth muscles).
Types of Muscle Tissue
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Skeletal Muscle:
- Attached to bones.
- Multiple, peripherally located nuclei.
- Striated.
- Voluntary and involuntary (reflexes).
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Smooth Muscle:
- Found in walls of hollow organs, blood vessels, eye, glands, and skin.
- Single, centrally located nucleus.
- Not striated.
- Involuntary, with gap junctions in visceral smooth.
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Cardiac Muscle:
- Found in the heart.
- Single, centrally located nucleus.
- Striated.
- Involuntary, with intercalated discs.
Skeletal Muscle Structure
- Most distinctive features: Striations and multinucleate.
- Muscle fibers: Muscle cells, ensheathed by endomysium.
- Sarcolemma: Plasma membrane of muscle fibers.
- Myofibrils: Inside muscle fibers, composed of myofilaments.
- Myofilaments: Composed of thick and thin filaments (myosin and actin).
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Sarcomere: Basic contractile unit.
- Contains thick filaments (myosin), thin filaments (actin), Z lines, M lines, and H bands
- These structural proteins contribute to elastic recoil, and anchor myosin during contraction.
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Connective tissues:
- Epimysium: Covers the entire muscle.
- Perimysium: Surrounds fascicles (bundles of muscle fibers).
- Endomysium: Surrounds individual muscle fibers.
Mechanisms of Contraction
- Sliding filament theory: Thin filaments (actin) slide over thick filaments (myosin).
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Cross-bridge cycle: Myosin heads bind to actin, pivot, detach, and re-cock for the next cycle.
- Step 1. Active-site exposure
- Step 2. Cross-bridge formation
- Step 3. Myosin head pivoting (power stroke)
- Step 4. Cross-bridge detachment
- Step 5. Myosin reactivation
Control of Contraction
- Troponin-tropomyosin system: Regulates cross-bridge attachment to actin.
- Calcium ions (Ca2+): Necessary for muscle contraction.
- Relaxation: When action potentials cease, Ca2+ is pumped back into the SR.
Excitation-Contraction Coupling
- Neuromuscular junction (NMJ): Where motor neuron meets muscle fiber.
- Acetylcholine (ACh): Neurotransmitter that triggers muscle action potentials.
- Action potential propagation: APs travel down T tubules, triggering Ca2+ release from SR.
Relationship of Action Potential
- Direct relationship between action potential, intracellular Ca2+ concentration, and muscle contraction.
Muscle Relaxation
- Action potential ceases.
- Ca2+-ATPase pumps move Ca2+ back into the SR.
- Cross-bridge formation stops.
Motor Units
- Motor neuron innervates a variable number of muscle fibers.
- Motor units vary in size based on needed precision of muscle control.
- Recruitment of motor units is important for increasing contraction strength.
Muscle Tone
- Skeletal muscles exhibit muscle tone in a resting state.
- Due to weak, involuntary contractions of motor units.
- Maintained by continually shifting activity of motor units.
- Essential for posture and supporting certain body positions.
Muscle Tone Abnormalities
- Hypotonia: Decreased or lost muscle tone.
- Hypertonia: Increased muscle tone.
Types of Muscle Contractions
- Isometric: Muscle produces tension but does not change length.
-
Isotonic: Muscle changes length and moves a load.
- Concentric: Muscle shortens while producing tension.
- Eccentric: Muscle lengthens while producing tension.
Types of Skeletal Muscle Fibers
- Type 1 (Slow Oxidative): Adapted for endurance.
- Type IIa (Intermediate): Mid-range of speed and endurance.
- Type IIx (Fast Glycolytic): Adapted for speed and power.
Homeostatic Imbalance Disorders
- Spasm/Cramp: Sudden, involuntary contraction of a muscle group.
- Muscle fatigue: Reduced ability to produce muscle tension.
- Delayed-onset muscle soreness (DOMS): Soreness 12–48 hours after strenuous exercise.
- Muscle tone abnormalities.
Muscle Repair
- Skeletal muscles have stem cells (satellite cells) near muscle fibers for repair and regeneration.
Muscle Decline With Aging
- Reduced muscle mass, reduced capillary blood supply, and fewer satellite cells.
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Description
Explore the fundamentals of the muscular system, including muscle tissue properties and classifications. This quiz covers voluntary and involuntary muscles, as well as the types of muscle tissue in the human body. Test your knowledge and understanding of how muscles function.