Muscle Tissue Overview
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Questions and Answers

What is the primary outcome of the phosphagen system during intense activities?

  • Net +1 ATP per cycle (correct)
  • Net +32 ATP per cycle
  • Net +2 ATP per cycle
  • Converts glucose into ATP

    • Which muscle fiber type primarily uses oxidative phosphorylation?

  • Type I (correct)
  • Type IIa
  • Type IIx
  • Type IIb

    • At what age does muscle mass generally begin to decline due to sarcopenia?

  • Age 40
  • Age 50
  • Age 20
  • Age 30 (correct)

    • What is the role of calmodulin in smooth muscle contraction?

    <p>Binds calcium to regulate contraction</p> Signup and view all the answers

    Which energy system produces lactate as a byproduct?

    <p>Glycolysis (anaerobic)</p> Signup and view all the answers

    What initiates the action potential in the sarcolemma?

    <p>Sodium ion influx and potassium ion efflux</p> Signup and view all the answers

    Which protein binds calcium ions during excitation-contraction coupling?

    <p>Troponin</p> Signup and view all the answers

    Which muscle contraction type occurs when the muscle length changes and the load remains constant?

    <p>Isotonic</p> Signup and view all the answers

    What physiological change occurs in skeletal muscle during disuse atrophy?

    <p>Irreversible degeneration of muscle tissue</p> Signup and view all the answers

    In which type of contraction does muscle tension change while the muscle length remains constant?

    <p>Isometric</p> Signup and view all the answers

    What factor primarily influences the frequency and intensity of muscle contractions?

    <p>Frequency &amp; intensity of stimulus</p> Signup and view all the answers

    Which of the following statements about the size principle is correct?

    <p>Smaller motor units are recruited first.</p> Signup and view all the answers

    What happens to calcium ions immediately after neuronal action potential ceases?

    <p>Calcium ions return to the sarcoplasmic reticulum.</p> Signup and view all the answers

    Which skeletal muscle fiber type is characterized by high force but high fatigability?

    <p>Type IIx</p> Signup and view all the answers

    What is the primary energy source required for muscle contraction?

    <p>ATP</p> Signup and view all the answers

    How does the regeneration capacity of smooth muscle compare to that of skeletal muscle?

    <p>Smooth muscle can regenerate indefinitely</p> Signup and view all the answers

    Which type of contraction is characterized by muscle shortening while performing work?

    <p>Concentric</p> Signup and view all the answers

    What is the main function of T-tubules in muscle contraction?

    <p>To propagate action potentials</p> Signup and view all the answers

    What type of contraction is typically used in rehabilitation settings to maintain a constant speed during muscle shortening and lengthening?

    <p>Isokinetic</p> Signup and view all the answers

    What typically happens when energy use rates exceed the rate of energy production during muscle activity?

    <p>Fatigue sets in.</p> Signup and view all the answers

    Which type of muscle tissue is characterized by striations and involuntary control?

    <p>Cardiac muscle</p> Signup and view all the answers

    What is the primary function of sarcoplasmic reticulum in muscle fibers?

    <p>Calcium ion storage and release</p> Signup and view all the answers

    What term describes the 'functional' contractile unit of muscle?

    <p>Sarcomere</p> Signup and view all the answers

    Which myofilament is responsible for pulling actin closer during muscle contraction?

    <p>Myosin</p> Signup and view all the answers

    During muscle contraction, what happens to the H-zone?

    <p>It disappears</p> Signup and view all the answers

    What is the primary role of satellite cells in muscle tissue?

    <p>Muscle repair and growth</p> Signup and view all the answers

    What initiates the sliding filament mechanism during muscle contraction?

    <p>Calcium binding to troponin</p> Signup and view all the answers

    Which component is NOT a part of the neuromuscular junction?

    <p>Sarcoplasmic reticulum</p> Signup and view all the answers

    In which state is the myosin head before it interacts with actin during contraction?

    <p>Low energy state</p> Signup and view all the answers

    Which characteristic of muscle tissue allows it to recoil after stretching?

    <p>Elasticity</p> Signup and view all the answers

    What is the primary reason skeletal muscles are classified as voluntary?

    <p>They require conscious control via the nervous system</p> Signup and view all the answers

    Which of the following statements about myofibers is incorrect?

    <p>They contain only actin filaments</p> Signup and view all the answers

    Which statement correctly describes the role of a motor unit?

    <p>It consists of a motor neuron and all the myofibers it innervates.</p> Signup and view all the answers

    In the process of excitation-contraction coupling, what does the neurotransmitter acetylcholine do?

    <p>Causes depolarization of the sarcolemma</p> Signup and view all the answers

    What is the primary function of the phosphagen system in the body?

    <p>It generates ATP from phosphocreatine</p> Signup and view all the answers

    Which muscle fiber type is primarily responsible for endurance activities?

    <p>Type I (Slow-oxidative)</p> Signup and view all the answers

    What happens to muscle mass after the age of 30?

    <p>It starts to decline due to sarcopenia</p> Signup and view all the answers

    Which energy system produces the highest net ATP yield per cycle?

    <p>Oxidative phosphorylation</p> Signup and view all the answers

    What characteristic distinguishes Type IIx muscle fibers?

    <p>They are fast-glycolytic and highly fatigable</p> Signup and view all the answers

    How do smooth muscle contractions compare to skeletal muscle contractions?

    <p>Smooth muscle can sustain contractions for longer periods</p> Signup and view all the answers

    Which of the following factors does NOT influence the strength of muscle contraction?

    <p>Age of the individual</p> Signup and view all the answers

    What is the primary regenerative capacity of smooth muscle compared to skeletal muscle?

    <p>Smooth muscle can regenerate more effectively than skeletal muscle</p> Signup and view all the answers

    What results from a muscle being paralyzed or immobilized?

    <p>Irreversible degeneration of muscle tissue</p> Signup and view all the answers

    Which type of muscle contraction is characterized by a constant load with changing muscle length?

    <p>Isotonic contraction</p> Signup and view all the answers

    What is the primary function of calcium ions during excitation-contraction coupling?

    <p>Bind to Troponin</p> Signup and view all the answers

    What occurs immediately after the action potential reaches the T-tubules?

    <p>Calcium channels in the sarcoplasmic reticulum open</p> Signup and view all the answers

    Which type of muscle contraction occurs when there is a constant load and muscle length changes?

    <p>Isotonic</p> Signup and view all the answers

    What determines the order of motor unit recruitment according to the size principle?

    <p>Motor units are recruited in the order of their size</p> Signup and view all the answers

    During muscle contractions, what happens to ATP levels as energy demands rise?

    <p>ATP is rapidly depleted</p> Signup and view all the answers

    What role does tropomyosin play in muscle contraction?

    <p>Blocks actin-binding sites</p> Signup and view all the answers

    In which circumstances is isokinetic contraction most commonly observed?

    <p>Rehabilitation and research settings</p> Signup and view all the answers

    What primarily happens to the sarcolemma during depolarization?

    <p>Facilitates sodium influx</p> Signup and view all the answers

    What can influence the selective recruitment of larger motor units during training?

    <p>Intensity of exercises performed</p> Signup and view all the answers

    How does muscle contraction cease after neuronal action potential ends?

    <p>Calcium is pumped back into the sarcoplasmic reticulum</p> Signup and view all the answers

    What is the primary characteristic that distinguishes cardiac muscle tissue from skeletal muscle tissue?

    <p>Cardiac muscle is only found in the heart</p> Signup and view all the answers

    Which component of the sarcomere is responsible for marking the ends of actin filaments?

    <p>Z-Disc</p> Signup and view all the answers

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

    <p>Binds calcium ions to trigger muscle contraction</p> Signup and view all the answers

    What is the main function of satellite cells within muscle tissue?

    <p>Differentiate into muscle tissue for repair and growth</p> Signup and view all the answers

    What happens to the H-zone during muscle contraction?

    <p>It shrinks and disappears</p> Signup and view all the answers

    What is the role of the T-tubules in muscle fibers?

    <p>Transmit action potential deep into the myofibrils</p> Signup and view all the answers

    What does the motor unit consist of?

    <p>One motor neuron and all the myofibers it innervates</p> Signup and view all the answers

    During the power stroke of muscle contraction, what happens to ADP and Pi?

    <p>They are released from the myosin head</p> Signup and view all the answers

    Which characteristic is NOT a main function of muscle tissue?

    <p>Protect internal organs</p> Signup and view all the answers

    What initiates muscle contractions at the neuromuscular junction?

    <p>Neurotransmitter release from the motor neuron</p> Signup and view all the answers

    In terms of energy, what is required for myosin heads to return to their low-energy state?

    <p>ATP</p> Signup and view all the answers

    What is the primary purpose of the sarcoplasmic reticulum in muscle fibers?

    <p>Store calcium ions</p> Signup and view all the answers

    Which type of muscle has striations and is under voluntary control?

    <p>Skeletal muscle</p> Signup and view all the answers

    Study Notes

    Muscle Tissue

    • Makes up approximately 42% of total body mass in males (AMAB) and 36% in females (AFAB).
    • Muscle-related tissues are often denoted by prefixes myo-, mys-, and sarco-.
    • There are three types of muscle tissue: skeletal, cardiac, and smooth.
      • Skeletal muscle is found in the body's framework, attached to bone and skin.
        • It is striated (meaning it appears striped under a microscope) and has voluntary control (we can consciously control its movement).
      • Cardiac muscle is found only in the heart (myocardium).
        • It is striated and has involuntary control (we cannot consciously control its beat).
      • Smooth muscle is found in the walls of hollow organs, including the digestive system, urinary bladder, blood vessels, and airways.
        • It is non-striated and has involuntary control.

    Muscle Tissue Characteristics and Functions

    • Four primary characteristics:

      • Excitability: ability to respond to stimuli.
      • Contractility: ability to shorten forcibly.
      • Extensibility: ability to be stretched.
      • Elasticity: ability to recoil to its original length.

    • Four main functions:

      • Produce movement: locomotion and joint manipulation.
      • Maintain body posture and position: keep the body upright.
      • Joint stabilization: keep joints from dislocating or overextending.
      • Generate heat: helps maintain thermoregulation and metabolism.

    Skeletal Muscle Makeup

    • Multilayered structure:
      • Muscle Belly: Entire muscle.
      • Epimysium: Connective tissue surrounding the entire muscle belly.
      • Fascicle: Bundle of muscle fibers.
      • Perimysium: Connective tissue surrounding each fascicle.
      • Myofiber: Muscle fiber, a single muscle cell.
      • Sarcolemma: Cell membrane of a myofiber.
      • Endomysium: Connective tissue surrounding each myofiber.
      • Sarcoplasm: Cytoplasm of a muscle fiber.
      • Myofibril: Bundle of sarcomeres, contains myofilaments.
      • Sarcomere: Contractile unit of skeletal muscle.

    Myofiber Structures

    • Mitochondria: Produce energy (ATP) for muscle contraction.
    • Sarcoplasmic Reticulum (SR): Release and reuptake calcium (Ca2+) ions which are essential for muscle contraction.
    • T-Tubules: Carry action potential from the sarcolemma deep into the myofiber, triggering calcium release from the SR.
    • Myonuclei: Contain DNA for the creation of new myofibrils.
    • Satellite cells: Muscle stem cells capable of differentiating into various muscle tissues, crucial for muscle growth and repair.

    Sarcomere Structure

    • Actin (thin) filaments: Contain three proteins:
      • Troponin: binds calcium (Ca2+).
      • Tropomyosin: covers myosin-binding sites on actin.
    • Myosin (thick) filaments: Contractile filaments that bind to and pull actin closer together.
    • Titin (elastic) filaments: Provide elasticity to the sarcomere.
    • Z-Disc: Ends of actin filaments, marking boundaries of the sarcomere.
    • M-Line: Midline of the sarcomere.
    • H-Zone: Region on either side of the M-Line with only myosin filaments (no actin-myosin overlap).

    Skeletal Muscle Contraction

    • Relaxed state: Sarcomeres and myofibers are at full length, with some actin-myosin overlap.
    • Contracted state: Sarcomeres and myofibers shorten due to the Sliding Filament Model.
      • Calcium binds to troponin, causing tropomyosin to move and expose myosin binding sites on actin.
      • Myosin heads bind to actin and pull the filaments past each other.
      • The H-zone shrinks and disappears as actin filaments slide over myosin filaments.

    Sliding Filament Model

    • The model describes the interaction between actin and myosin filaments during muscle contraction.
    • Resting State: Myosin head is in a low-energy state with ATP bound to it, not yet attached to actin.
    • Cross-bridge Formation: ATP hydrolyzes, and the myosin head becomes energized and attaches to a binding site on actin, forming a cross-bridge.
    • Power Stroke: ADP and Pi are released, triggering the myosin tail to contract and pull actin.
      • This movement shortens the sarcomere.
    • Cleavage: A new ATP molecule binds to the myosin head, causing it to detach from actin.
      • This returns it to a low-energy state.
    • Cross-bridge Cycling: These steps repeat as long as calcium is available and ATP is present.

    Excitation-Contraction Coupling

    • The process of converting an electrical signal (action potential) into a muscle contraction.
    • Motor Unit: Comprises a motor neuron and all the muscle fibers it innervates.
    • Neuromuscular Junction: The site where a motor neuron communicates with a muscle fiber.
      • Synaptic Vesicles: Store acetylcholine (ACh) in the neuron's axon.
      • Synaptic Cleft: Space between the neuron's axon and the sarcolemma.
      • End-Plate Receptors: Binding proteins on the sarcolemma specific for ACh.

    Membrane Potential

    • The sarcolemma is a polarized membrane, maintaining a negative charge at rest.
    • A motor neuron stimulus causes depolarization of the sarcolemma, altering the charge and initiating an action potential.

    Excitation-Contraction Coupling Steps

    1. Neuron Releases ACh: ACh from the motor neuron binds to end-plate receptors, opening ligand-gated channels.
    2. Sarcolemma Depolarizes: Ion flow across the membrane, facilitated by the open channels, causes membrane potential to rise.
      • This triggers voltage-gated channels to open.
    3. Action Potential Propagates: The action potential travels down the sarcolemma.
    4. T-Tubules: The action potential reaches T-tubules and activates voltage-sensitive proteins, opening Ca2+ channels in the SR.
    5. Calcium Release: Calcium ions flood the sarcoplasm, binding to troponin.
    6. Sliding Filament Model: Muscle contraction occurs as myosin heads bind to actin.
    7. Calcium Reuptake: After the neuronal signal ceases, Ca2+ is pumped back into the SR, tropomyosin covers the binding sites, and muscle relaxation occurs.

    Size Principle

    • Motor units are recruited in order of size, with smaller motor units (lower force, finer motor control) activated first, and larger motor units (higher force) recruited later.
    • This allows for efficient and controlled muscle force generation.

    Muscle Contractions

    • Three main types:
      • Isometric: Muscle tension changes, but muscle length remains constant, often used in rehabilitation.
      • Isotonic: Muscle tension is constant, but muscle moves through a range of motion.
        • Concentric: Muscle shortens while generating force.
        • Eccentric: Muscle lengthens while generating force, often used to stabilize joints during motion.
      • Isokinetic: Muscle tension varies, but the movement speed is constant, often used in research and rehabilitation settings.

    Energy for Muscle Contractions

    • ATP is the primary energy source for muscle contraction.
    • ATP stores are limited, lasting only ~4-6 seconds.
    • Muscle fatigue arises when energy use rates exceed energy replenishment rates.

    Energy Systems

    • 3 primary systems:
      • Phosphagen (PCr) System: Most immediate ATP source, lasts ~15 seconds.
      • Glycolysis: Converts glucose to ATP, lasts ~60 seconds (anaerobically) or until glucose is depleted (aerobically).
      • Oxidative Phosphorylation: Uses pyruvate to generate ATP via Krebs Cycle and Electron Transport Chain, lasts until fuel sources are depleted.

    Skeletal Muscle Fiber Typing

    • Classified based on their primary energy system:
      • Type IIx (Fast-glycolytic): Primarily rely on PCr and anaerobic glycolysis, high force and power, highly fatigable.
      • Type IIa (Fast-oxidative): Utilize both anaerobic glycolysis and oxidative phosphorylation, moderate force and power, moderately fatigable.
      • Type I (Slow-oxidative): Primarily rely on oxidative phosphorylation, low force and power, fatigue-resistant.

    Muscle Development & Decay

    • Muscle development follows a pattern from head to toe, reaching peak control in mid-adolescence.
    • After age 30, muscle mass declines (sarcopenia), and muscle fibers are replaced by connective tissue.
    • Disuse Atrophy: Muscle tissue irreversibly degenerates with immobility or paralysis (muscle mass can shrink to 25% of its original size).
    • Exercise and training can help maintain or even reverse muscle decline.

    Smooth Muscle

    • Compared to skeletal muscle, smooth muscle:
      • Has fewer myosin filaments.
        • Actin uses calmodulin instead of troponin to bind calcium (though still has tropomyosin).
      • Less forceful and powerful, but more efficient.
        • Slower contractions and relaxations, but can maintain contractions for longer durations.
        • Lower energy cost.
      • Regenerates throughout life, unlike skeletal muscle.

    Summary

    • Muscles are multilayered structures with integrated functions.
    • Contraction is initiated by the motor neuron at the neuromuscular junction, leading to calcium release and the Sliding Filament Model.
    • Muscle force is regulated by the frequency and intensity of the stimulus and the Size Principle.
    • Fiber types are categorized by their energy systems and fatigability.
    • Muscle contractions can be isometric, isotonic, or isokinetic, depending on load, length, and speed of movement.
    • The three energy systems provide ATP for muscle contraction, each with different durations and capabilities.

    Muscle Tissue

    • Makes up 42% of total body mass in males (AMAB) and 36% in females (AFAB)
    • Terms related to muscle are denoted with prefixes myo-, mys-, and sarco-
    • Three types of muscle tissue: skeletal, cardiac, and smooth

    Skeletal Muscle Makeup

    • Muscles are multi-layered structures:
      • Muscle belly is surrounded by epimysium
      • Fascicles are surrounded by perimysium
      • Myofibers are surrounded by sarcolemma and endomysium
      • Myofibrils are surrounded by sarcomere

    Myofiber Structures

    • These structures aid in myofiber function:
      • Mitochondria: produce energy (ATP)
      • Sarcoplasmic Reticulum: releases and retakes calcium (Ca2+) ions
      • T-Tubules: carry action potential from the sarcolemma deep into the myofiber
      • Myonuclei: contain DNA for the creation of new myofibrils
      • Satellite cells: "muscle stem cells" that can differentiate into necessary tissue

    Sarcomere Structure

    • Composed of three myofilaments
      • Actin (thin): Contains troponin and tropomyosin
      • Myosin (thick): Contractile filaments that bind to and pull actin
      • Titin (elastic): gives sarcomere its elasticity
    • Key demarcations:
      • Z-Disc: ends of Actin filaments; demarcate ends of sarcomere
      • M-Line: midline of sarcomere
      • H-zone: area with no actin-myosin overlap

    Skeletal Muscle Contraction

    • When a muscle is relaxed:
      • Sarcomeres and myofibers are at full length
      • Some actin-myosin overlap
      • M-Line and H-Zone are distinct
    • When a muscle contracts:
      • Sarcomeres and myofibers shorten
      • Sliding Filament Model: calcium binds to troponin and ATP hydrolysis causes myosin to bind to actin, forming a cross-bridge, which pulls actin towards the M-Line.

    Sliding Filament Model

    • Myosin head in the “low energy” state (ATP bonded): Not yet attached to actin
    • ATP Hydrolysis: Myosin head energizes and attaches to actin
    • Power Stroke: ADP & Pi are released, and the myosin tail contracts, pulling the actin-myosin bridge closer to the M-Line, shortening the sarcomere
    • Cleavage: New ATP binds to myosin head, causing it to detach from its binding site on actin
    • Cross-Bridge Cycling: Cycle repeats as long as calcium and ATP are available.

    Excitation-Contraction Coupling

    • Goal: Convert electrical signal (brain) to chemical signal (neurotransmitter release)
    • Motor Unit: Motor neuron and all the myofibers it innervates
    • Neuromuscular Junction: Where motor neuron meets its fiber group (Synaptic Vesicles, Synaptic Cleft, End-Plate Receptors)

    Membrane Potential

    • Sarcolemma is polarized (holds a negative charge)
    • Motor neuron stimuli depolarize the sarcolemma (flip the charge) generating an action potential by causing ion shuttling across the membrane

    Size Principle

    • Motor units are recruited in order of size, smaller motor units first (for finer motor tasks) and larger motor units last (for higher forces)
    • Allows for orderly recruitment of muscle fibers

    Muscle Contractions

    • Three main types:
      • Isometric: External load changes but muscle length remains constant
      • Isotonic: External load is constant but muscle length changes
        • Concentric: muscle shortening (does work)
        • Eccentric: muscle lengthening (resists work)
      • Isokinetic: External load varies as muscle length changes so that the movement speed is constant

    Energy for Contractions

    • Muscles need ATP to contract
    • ATP stores only last for ~4-6 seconds
    • Fatigue occurs when energy use exceeds the rate of energy production

    Energy Systems

    • Three main energy systems:
      • Phosphagen (PCr) system: Most immediate source of ATP; anaerobic; lasts ~15 seconds
      • Glycolysis: Conversion of glucose into ATP; can be anaerobic or aerobic; lasts ~60 seconds
      • Oxidative Phosphorylation: Uses pyruvate from glycolysis to generate ATP; aerobic; lasts until all fuel sources are depleted

    Skeletal Muscle Fiber Typing

    • Three types of fibers based on primary energy system:
      • Type IIx (Fast-glycolytic): Rely on PCr and anaerobic glycolysis; high force and power, highly fatigable
      • Type IIa (Fast-oxidative): Use combination of anaerobic glycolysis and oxidative phosphorylation; moderate force and power, moderately fatigable
      • Type I (Slow-oxidative): Rely on oxidative phosphorylation; low force and power, fatigue-resistant

    Muscle Development & Decay

    • In infancy, muscle development reflects changes in neuromuscular control
    • Muscle mass begins to decline after age 30 (sarcopenia)
    • Paralysis, immobilization, or bedridden states can lead to irreversible muscle degeneration (disuse atrophy)
    • Muscle strength relative to body mass is similar between genders

    Smooth Muscle

    • Fewer myosin filaments
    • Actin has calmodulin that binds calcium
    • Less forceful, but more efficient than skeletal muscle
    • Regenerates throughout the lifespan

    Muscle Tissue Summary

    • Muscles are multilayered structures, require coordination of innervation
    • Contractions are carried out through excitation-contraction coupling
    • Muscle strength is regulated by frequency and intensity of stimulus along with size principle
    • Muscle fibers are classified based on energy systems and have varying fatigabilities
    • Muscle contractions can be isometric, isotonic, or isokinetic based on changes in load, muscle length, and movement speed.

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    Description

    Explore the different types and characteristics of muscle tissue. This quiz covers skeletal, cardiac, and smooth muscle, along with their functions in the human body. Test your understanding of muscle tissue and its importance in our body system.

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