Muscle Physiology Quiz
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Questions and Answers

What is the primary characteristic of isometric muscle contraction?

  • No change in muscle tension or muscle length.
  • Changes in muscle length without a change in tension.
  • Changes in muscle length with a constant level of tension.
  • No change in muscle length while generating tension. (correct)

    • Which metabolic process is responsible for meeting 95% of a muscle cell's ATP demands?

  • Aerobic metabolism (correct)
  • Glycolysis
  • Anaerobic metabolism
  • Creatine phosphate system

    • In isotonic muscle contraction, what changes occur as muscle tension is increased?

  • The muscle lengthens while bearing the constant load.
  • The muscle neither shortens nor lengthens.
  • The muscle maintains a constant length as tension increases.
  • The muscle shortens and lifts the constant load. (correct)

    • Which process primarily explains the mechanism of tetanus in muscle physiology?

    <p>Repeated stimulation leading to a cumulative increase in intracellular calcium ions. (C)</p> Signup and view all the answers

    How many ATP molecules are produced from one pyruvic acid molecule during aerobic metabolism via the Kreb's cycle?

    <p>17 ATP (C)</p> Signup and view all the answers

    During anaerobic metabolism, what are the end products of glycolysis?

    <p>2 pyruvic acids and 2 ATP (D)</p> Signup and view all the answers

    A person is holding a heavy box steady. What type of muscle contraction is primarily occurring in their arms?

    <p>Isometric contraction only (A)</p> Signup and view all the answers

    What directly triggers the movement of tropomyosin away from the myosin binding sites on actin?

    <p>The binding of calcium ions to troponin (D)</p> Signup and view all the answers

    What is the direct result of extended cross-bridge cycling during tetanus?

    <p>Prolonged muscle contraction without relaxation (B)</p> Signup and view all the answers

    During the contraction cycle, what event directly follows the hydrolysis of ATP?

    <p>Attachment of myosin to actin to form cross-bridges (B)</p> Signup and view all the answers

    Which of the following conditions must be met for the contraction cycle to continue?

    <p>High ATP levels and high calcium ion concentration (B)</p> Signup and view all the answers

    According to the sliding filament mechanism, what happens to the I band and H zone during maximal muscle contraction?

    <p>They narrow and eventually disappear (A)</p> Signup and view all the answers

    During muscle contraction, what happens to the length of the A band?

    <p>It remains unchanged. (A)</p> Signup and view all the answers

    How does the sliding filament mechanism explain muscle contraction?

    <p>Myosin heads attach to actin and 'walk' along the thin filaments, pulling them toward the M line (C)</p> Signup and view all the answers

    If a muscle cell runs out of ATP, which stage of the contraction cycle would be directly affected?

    <p>Detachment of myosin from actin (A)</p> Signup and view all the answers

    Which of the following factors does NOT directly determine the strength of skeletal muscle contraction?

    <p>Number of muscle fibers in the muscle (C)</p> Signup and view all the answers

    What is the role of the M line in the sliding filament mechanism?

    <p>It is where the thin filaments attach and are pulled towards during contraction (A)</p> Signup and view all the answers

    How does shortening the sarcomere affect the amount of tension that can be generated?

    <p>It decreases tension because there is less room for actin-myosin overlap. (C)</p> Signup and view all the answers

    Regulation of muscle contraction is controlled by which part of the nervous system?

    <p>Somatic nervous system (C)</p> Signup and view all the answers

    Which event occurs immediately after the power stroke in the contraction cycle, assuming ATP is available?

    <p>Detachment of myosin from actin (B)</p> Signup and view all the answers

    What is the primary determinant of the amount of tension a muscle can generate, according to the length-tension relationship?

    <p>The extent of actin-myosin myofilament overlap. (D)</p> Signup and view all the answers

    Which scenario would lead to a DECREASE in the force of skeletal muscle contraction?

    <p>Muscle fiber length stretched significantly beyond its optimal length (C)</p> Signup and view all the answers

    How does the recruitment of motor units affect muscle contraction?

    <p>It increases the force of contraction by activating more muscle fibers. (A)</p> Signup and view all the answers

    Which of the following is a direct result of metabolic fatigue on muscle contraction?

    <p>Reduced force generation (A)</p> Signup and view all the answers

    In Myasthenia Gravis, which component of the neuromuscular junction is targeted by the autoimmune response?

    <p>Nicotinic acetylcholine receptor (D)</p> Signup and view all the answers

    What initial symptoms are most commonly observed in individuals diagnosed with Myasthenia Gravis?

    <p>Double vision and difficulty swallowing (B)</p> Signup and view all the answers

    Which of the following treatments is commonly used to manage Myasthenia Gravis by improving neuromuscular transmission?

    <p>Acetylcholinesterase inhibitors to increase acetylcholine availability (C)</p> Signup and view all the answers

    Which of the following best describes the primary role of synaptic vesicles in the neuromuscular junction?

    <p>To store and release neurotransmitters like acetylcholine (ACh). (B)</p> Signup and view all the answers

    What is the role of the motor end plate in the Neuromuscular Junction?

    <p>It contains receptors for Acetylcholine. (C)</p> Signup and view all the answers

    Considering the sequence of events in excitation-contraction coupling, what is the direct result of an action potential spreading down the T-tubules?

    <p>Release of $Ca^{++}$ ions from the sarcoplasmic reticulum (B)</p> Signup and view all the answers

    In the context of the neuromuscular junction, what is the primary function of acetylcholinesterase?

    <p>To break down acetylcholine (ACh) in the synaptic cleft. (D)</p> Signup and view all the answers

    Which of the following accurately describes the role of acetylcholine (ACh) in the process of excitation-contraction coupling?

    <p>ACh diffuses to receptors on the sarcolemma, leading to the opening of $Na^+$ channels. (B)</p> Signup and view all the answers

    How does the structural arrangement at the neuromuscular junction facilitate rapid and efficient communication between a motor neuron and a muscle fiber?

    <p>The close proximity of the axon terminal to the motor end plate, separated by the synaptic cleft, allows for rapid neurotransmitter diffusion. (D)</p> Signup and view all the answers

    What is the primary effect of $Na^+$ ions rushing into the muscle cell during excitation-contraction coupling?

    <p>Depolarization of the sarcolemma (C)</p> Signup and view all the answers

    A patient is diagnosed with a condition that prevents the release of acetylcholine at the neuromuscular junction. Which step in the excitation-contraction coupling would be directly affected?

    <p>Binding of acetylcholine to receptors on the sarcolemma (C)</p> Signup and view all the answers

    Which characteristic is unique to cardiac muscle tissue?

    <p>It contains intercalated discs. (D)</p> Signup and view all the answers

    How do acetylcholinesterase inhibitors alleviate the symptoms of Myasthenia Gravis?

    <p>By preventing the breakdown of acetylcholine in the synaptic cleft (C)</p> Signup and view all the answers

    How does smooth muscle contraction differ fundamentally from skeletal muscle contraction?

    <p>Smooth muscle relies on myosin light chain kinase (MLCK) for cross-bridge activation, while skeletal muscle uses troponin-tropomyosin. (C)</p> Signup and view all the answers

    Which of the following characteristics is most closely associated with slow-twitch (Type I) muscle fibers?

    <p>High resistance to fatigue (D)</p> Signup and view all the answers

    What is the primary mechanism behind muscle fatigue during intense, short-duration exercise?

    <p>Accumulation of lactic acid and other metabolites, disrupting muscle pH and enzyme function. (D)</p> Signup and view all the answers

    What is the primary cause of muscle fatigue during intense, short-duration exercise?

    <p>Inadequate release of calcium ions from the sarcoplasmic reticulum. (C)</p> Signup and view all the answers

    Which of the following characteristics is LEAST associated with fast glycolytic muscle fibers?

    <p>Abundant mitochondria (B)</p> Signup and view all the answers

    Rigor mortis, the stiffening of muscles after death, is a direct result of which of the following?

    <p>Complete depletion of ATP and phosphorylcreatine. (D)</p> Signup and view all the answers

    Which type of muscle fiber is best suited for activities requiring prolonged, sustained contractions, such as maintaining posture?

    <p>Slow oxidative (slow-twitch) (B)</p> Signup and view all the answers

    If a muscle fiber is described as 'red' and having 'abundant mitochondria', it is most likely what type of fiber?

    <p>Slow oxidative (C)</p> Signup and view all the answers

    What is the role of ATP in the context of muscle rigor?

    <p>ATP is needed for cross-bridge detachment, allowing the muscle to relax. (C)</p> Signup and view all the answers

    A weightlifter is performing a set of heavy squats. Which type of muscle fibers are MOST likely being heavily recruited during this activity?

    <p>Predominantly fast glycolytic fibers due to the high force and short duration of the activity. (A)</p> Signup and view all the answers

    Which metabolic process is primarily utilized by fast glycolytic muscle fibers to produce energy for contraction?

    <p>Anaerobic glycolysis (D)</p> Signup and view all the answers

    Flashcards

    Muscle Fatigue

    A decline in muscle performance due to prolonged activity, resulting from factors like energy depletion and lactic acid accumulation.

    Types of Muscle Fibers

    There are three types: Type I (slow-twitch), Type IIa (fast-twitch), and Type IIb (fast-twitch, fatigue-prone), each with different functionalities.

    Cardiac Muscle

    A type of involuntary muscle with striations, intercalated discs, and a branched structure, specialized for continuous contraction.

    Smooth Muscle

    Involuntary, non-striated muscle found in organs, responsible for slow, sustained contractions.

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    Skeletal Muscle vs Smooth Muscle

    Skeletal muscle is voluntary and striated, while smooth muscle is involuntary and non-striated, differing in control and structure.

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    Neuromuscular Junction

    The connection between a motor neuron and a muscle fiber, including axon terminal, motor end plate, and synaptic cleft.

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    Axon Terminal

    The end part of a motor neuron where neurotransmitters are stored and released into the synaptic cleft.

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    Synaptic Cleft

    The space between the axon terminal and motor end plate where neurotransmitters are released during muscle activation.

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    Myasthenia Gravis

    An autoimmune neuromuscular disease targeting acetylcholine receptors.

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    Nicotinic Acetylcholine Receptor

    A receptor that binds acetylcholine and is crucial for muscle contraction.

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    Acetylcholinesterase Inhibitors

    Medications that inhibit the breakdown of acetylcholine to improve muscle activation.

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    Excitation-Contraction Coupling

    The process linking nerve impulses to muscle contraction through calcium release.

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    Sarcoplasmic Reticulum

    An organelle that stores and releases calcium ions for muscle contraction.

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    ACh Release

    Acetylcholine is released from synaptic vesicles into the synaptic cleft.

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    Action Potential

    An electrical impulse that triggers muscle contraction after binding of ACh.

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    Calcium Ions (Ca++)

    Ions released by the sarcoplasmic reticulum that initiate muscle contraction.

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    A band

    The dark stripe in a muscle fiber representing thick filaments and unchanged width during contraction.

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    Skeletal muscle contraction factors

    Factors influencing contraction strength include metabolic conditions, load, motor unit recruitment, fiber length, and stimulation frequency.

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    Metabolic conditions

    Physical state influencing muscle contraction, like fatigue from prolonged activity.

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    Load in muscle contraction

    The amount of weight a muscle must lift affects its contraction strength.

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    Recruitment of motor units

    Activating more motor units increases muscle contraction force and strength.

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    Initial length of muscle fibers

    The starting length of muscle fibers affects the tension they can produce when contracting.

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    Frequency of stimulation

    The rate at which a muscle is stimulated influences the strength and duration of contraction.

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    Length-tension relationship

    The tension generated by a muscle is related to the overlap of actin and myosin filaments.

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    Sarcoplasm

    The cytoplasm of muscle cells where important reactions occur during contraction.

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    Troponin

    A protein that binds calcium ions and moves tropomyosin to expose myosin binding sites on actin.

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    Tropomyosin

    A protein that blocks myosin binding sites on actin when muscle is relaxed.

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    Contraction Cycle

    The series of events that allow muscle contraction through sliding filaments.

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    ATP Hydrolysis

    The process that provides energy during the first step of muscle contraction.

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    Cross-Bridge Formation

    The attachment of myosin heads to actin to initiate muscle contraction.

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    Power Stroke

    The action that pulls the thin filaments toward the M line during contraction.

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    Sliding Filament Mechanism

    The theory explaining how muscle fibers shorten during contraction by filaments sliding past each other.

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    Isometric Muscle Contraction

    A muscle contraction where the muscle length does not change while exerting tension.

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    Isotonic Muscle Contraction

    A muscle contraction where muscle length changes while producing a constant force.

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    Mechanism of Tetanus

    A state where repeated stimulation leads to sustained muscle contraction without relaxation due to high calcium levels.

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    Aerobic Metabolism

    Energy production method using oxygen, primarily through the Kreb's cycle, generating ATP.

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    Anaerobic Metabolism

    Energy production without oxygen, primarily through glycolysis, producing less ATP than aerobic.

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    Cross-bridge Cycling

    The process by which muscles generate force through attachment and movement of myosin heads on actin filaments.

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    Intracellular Calcium Ions

    Calcium ions inside muscle cells that are crucial for initiating contraction and sustaining tetanus.

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    Kreb's Cycle

    A metabolic pathway that produces ATP through the oxidation of pyruvic acid in aerobic metabolism.

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    Lactic Acid Buildup

    A byproduct of anaerobic metabolism that contributes to muscle fatigue.

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    Acetylcholine Release Failure

    When action potentials cannot stimulate the motor neuron to release acetylcholine.

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    Muscle Fiber Classification

    Muscle fibers are classified into slow oxidative, oxidative-glycolytic, and fast glycolytic.

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    Slow Oxidative Fibers

    Muscle fibers that are red, abundant in mitochondria, and used for prolonged activity.

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    Fast Glycolytic Fibers

    Muscle fibers that are white, low in mitochondria, and suited for short bursts of power.

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    Muscle Rigor

    A state of rigidity in muscles caused by depletion of ATP and phosphorylcreatine.

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    Rigor Mortis

    The postmortem condition where muscles stiffen due to ATP depletion.

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    Study Notes

    Muscle Physiology

    • Muscle physiology is a study of how muscles work.
    • Muscle contraction is regulated by the somatic nervous system.
    • The strength of skeletal muscle contraction is determined by metabolic conditions, amount of load, motor unit recruitment, muscle fiber length, and frequency of stimulation.

    Neuromuscular Junction

    • The neuromuscular junction is formed by the axon terminal and the motor end plate.
    • The axon terminal is the end of a motor neuron axon, containing synaptic vesicles that release acetylcholine (ACh).
    • The motor end plate is a specific part of the sarcolemma that contains ACh receptors.
    • The synaptic cleft is the space between the axon terminal and the muscle fiber.

    Excitation-Contraction Coupling

    • Nerve impulse triggers the release of acetylcholine (ACh).
    • ACh binds to receptors on the sarcolemma, opening Na+ channels and generating a muscle action potential.
    • The muscle action potential travels down the sarcolemma and T-tubules.
    • The sarcoplasmic reticulum releases calcium ions (Ca²⁺).
    • Ca²⁺ binds to troponin, moving tropomyosin.
    • Myosin binding sites are exposed, allowing myosin to bind to actin and begin the contraction cycle.

    Contraction Cycle

    • ATP hydrolysis prepares myosin for binding.
    • Myosin binds to actin, forming a cross-bridge.
    • Power stroke moves filaments.
    • Myosin detaches from actin.
    • The cycle repeats as long as ATP and calcium are available.

    The Sliding Filament Mechanism

    • Muscle contraction occurs due to the sliding of actin and myosin filaments.
    • The I band and H zone narrow during contraction.
    • The A band remains the same width.

    Relaxation

    • Ca²⁺ is pumped back into the sarcoplasmic reticulum.
    • Troponin returns to its original position.
    • Tropomyosin blocks myosin-binding sites on actin.
    • The muscle relaxes.

    Determinants of Contraction Force

    • Muscle contraction is influenced by metabolic conditions (e.g., fatigue), load, motor unit recruitment, initial muscle fiber length, and stimulation frequency.

    Length-tension Relationship

    • Tension generation is determined by the amount of actin-myosin overlap.
    • Optimal overlap leads to maximal tension.
    • Over-stretched or shortened muscles generate less tension.

    Twitch Contraction

    • A twitch contraction is a brief and complete muscle contraction following a single nerve impulse.
    • A myogram records muscle contractions, including latent, contraction, and relaxation periods.
    • The refractory period is the time after a contraction when the muscle cannot be stimulated.

    Types of Contraction

    • Twitch contractions are single, brief contractions.
    • Summation occurs when twitches combine due to high frequency stimulation, leading to sustained contraction (tetanus).
    • Graded contractions vary in strength based on the number of muscle fibers recruited.

    Mechanism of Tetanus

    • Muscle stimulation occurs repeatedly.
    • There is a cumulative increase in intracellular calcium ions.
    • Cycling of cross bridges is extended.
    • The muscle does not relax (tetanus).

    Muscle Metabolism

    • Aerobic metabolism provides 95% of energy for muscle activity, via Kreb's cycle (17 ATP per pyruvic acid molecule).
    • Anaerobic metabolism (glycolysis) produces 2 pyruvic acids and 2 ATP, with pyruvic acid converted to lactic acid if oxygen is low.
    • Creatine phosphate stores energy to replenish ATP during rapid muscle activity.

    Muscle Fatigue

    • Muscle fatigue is the inability of muscles to maintain their output.
    • Factors contributing to muscle fatigue include depletion of metabolic reserves (oxygen, glycogen, creatine phosphate), reduced calcium concentration, build-up of lactic acid and ADP, and failure of action potential.

    Classification of Muscle Fibers

    • Muscle fibers are categorized as slow oxidative (red), oxidative-glycolytic (red-fast twitch A), and fast glycolytic (white).
    • Oxidative fibers are specialized for prolonged, sustained contraction.
    • Glycolytic fibers are better for short, powerful contractions.

    Muscle Rigor

    • Rigor occurs when ATP and creatine phosphate are completely depleted.
    • Rigor mortis is the post-mortem rigidity of muscles.

    Cardiac Muscle

    • Cardiac muscle is branched, cylindrical, and contains one central nucleus
    • Intercalated discs join neighboring fibers.
    • Intercalated discs contain gap junctions and desmosomes.
    • Cardiac muscle is involuntary and autorhythmic.

    Smooth Muscle

    • Smooth muscle is thickest in the middle and tapers at the ends. Each cell has one centrally located nucleus, not striated.
    • Smooth muscle is located in the walls of hollow organs, airways, blood vessels.
    • Smooth muscle is involuntary and can stretch and shorten to a greater degree than other muscle types.
    • Smooth muscle contraction is slower and has a longer contraction period compared to skeletal muscle.
    • It has very few sarcoplasmic reticulum compared to other muscle types, releasing calcium ions from the interstitial fluid.
    • Smooth muscle has caveolae.
    • It uses calmodulin instead of troponin in the regulation step.
    • Smooth muscle contraction is regulated by nerve impulses, hormones, stretching, local factors, and changes in pH, oxygen, and carbon dioxide levels, and ions.

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