Skeletal Muscle Physiology
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Questions and Answers

What is the main function of skeletal muscle?

  • Respiration
  • Locomotion (correct)
  • Blood circulation
  • Digestion

    • Which type of muscle is controlled consciously?

  • Cardiac muscle
  • Smooth muscle
  • Involuntary muscle
  • Striated muscle (correct)

    • What is the property of muscles that allows them to generate tension?

  • Extensibility
  • Elasticity
  • Excitability
  • Contractility (correct)

    • Where can smooth muscles typically be found?

    <p>In the walls of blood vessels and internal organs</p> Signup and view all the answers

    Which type of muscle controls itself with the help of the nervous and endocrine systems?

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

    What is the capacity of a muscle to receive and respond to stimuli?

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

    What is the specialized organelle responsible for storing, releasing, and reuptake of ion calcium in a muscle fiber?

    <p>Sarcoplasmic Reticulum (SR)</p> Signup and view all the answers

    Which protein makes up the thick filament in a sarcomere responsible for muscle contraction?

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

    What component of an actin filament is responsible for regulating the interaction between actin and myosin during muscle contraction?

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

    What allows for rapid transmission of the action potential into a muscle cell?

    <p>T-Tubules</p> Signup and view all the answers

    What is the event that leads to a rapid change in membrane potential in a muscle cell?

    <p>Action Potential</p> Signup and view all the answers

    According to the Sliding Filament Model, why does a muscle shorten or lengthen?

    <p>Due to thick and thin filaments sliding over each other</p> Signup and view all the answers

    What is the primary function of the myofilaments in muscle contraction?

    <p>To shorten the sarcomere and cause muscle contraction</p> Signup and view all the answers

    What is the primary role of the troponin complex within the thin filament?

    <p>To regulate the exposure of the actin binding sites on the thin filament</p> Signup and view all the answers

    How do the mitochondria in slow-twitch muscle fibers differ from those in fast-twitch fibers?

    <p>Slow-twitch fibers have more mitochondria to provide a greater supply of ATP for prolonged activity</p> Signup and view all the answers

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

    <p>To regulate the uptake and release of calcium ions during contraction</p> Signup and view all the answers

    What is the primary role of the myosin heads within the thick filament?

    <p>To act as binding sites for the actin filaments during contraction</p> Signup and view all the answers

    What is the primary role of the connective tissue layers (epimysium, perimysium, and endomysium) surrounding the skeletal muscle fibers?

    <p>To provide strength, stability, and prevent tearing of the muscle during contraction</p> Signup and view all the answers

    What happens once myosin binds with actin in muscle fiber action?

    <p>The myosin head tilts and pulls the actin filament.</p> Signup and view all the answers

    What is the main function of Type I muscle fibers?

    <p>High aerobic endurance</p> Signup and view all the answers

    Which type of muscle fiber is better for explosive activities?

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

    What is the contractile speed of Type IIa muscle fibers?

    <p>50 ms</p> Signup and view all the answers

    Which type of muscle fiber has low aerobic capacity and high anaerobic capacity?

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

    How many fibers per motor neuron are present in Type IIa muscle fibers?

    <p>110-250</p> Signup and view all the answers

    What are the three types of muscle found in the human body?

    <p>Skeletal, Smooth, and Cardiac</p> Signup and view all the answers

    What is the primary function of skeletal muscle?

    <p>To enable voluntary movement of the body</p> Signup and view all the answers

    Which of the following is NOT a property of muscle fibers?

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

    What is the name of the connective tissue that surrounds the entire muscle?

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

    What is the name of the connective tissue that surrounds each fascicle (bundle) of muscle fibers?

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

    What are the structures responsible for muscle contraction?

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

    What is the main property of skeletal muscle that enables it to perform its functions effectively?

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

    Which type of muscle is found in the walls of blood vessels and internal organs?

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

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

    <p>To store and release calcium ions</p> Signup and view all the answers

    Which type of muscle fiber is better suited for explosive activities?

    <p>Type IIb (fast-twitch) muscle fibers</p> Signup and view all the answers

    What is the name of the connective tissue that surrounds the entire muscle?

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

    According to the Sliding Filament Model, why does a muscle shorten or lengthen?

    <p>Due to the movement of the myosin and actin filaments relative to each other</p> Signup and view all the answers

    Which organelle acts as the power plant of ATP in muscle cells?

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

    In a sarcomere, what is the function of Troponin I within the thin filament?

    <p>Inhibition of actin-myosin interaction</p> Signup and view all the answers

    What is the primary function of the light chain on a myosin molecule?

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

    Which component of a myosin filament serves as an ATPase enzyme?

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

    What is the role of Tropomyosin in muscle contraction?

    <p>Inhibition of actin-myosin interaction</p> Signup and view all the answers

    How do slow-twitch muscle fibers differ from fast-twitch fibers in terms of mitochondria?

    <p>Slow-twitch fibers have fewer mitochondria</p> Signup and view all the answers

    What is the primary function of the sarcoplasmic reticulum in a muscle fiber?

    <p>To store, release, and reuptake calcium ions</p> Signup and view all the answers

    According to the Sliding Filament Model, what is the primary reason a muscle shortens or lengthens?

    <p>The thick and thin filaments slide over each other without changing length</p> Signup and view all the answers

    What is the primary role of the $t$-tubules in a muscle fiber?

    <p>To allow for rapid transmission of the action potential into the cell</p> Signup and view all the answers

    What is the main component of the thin filament responsible for regulating the interaction between actin and myosin during muscle contraction?

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

    What is the primary function of the myosin heads within the thick filament?

    <p>To generate force and movement during muscle contraction</p> Signup and view all the answers

    Which type of muscle fiber is better suited for explosive activities?

    <p>Type IIb (fast-twitch) muscle fibers</p> Signup and view all the answers

    What is the role of ATP in muscle contraction according to the Sliding Filament Model?

    <p>Provides energy for muscle action</p> Signup and view all the answers

    What is the immediate result of the cleavage of ATP by ATPase in muscle contraction?

    <p>Formation of ADP and Pi</p> Signup and view all the answers

    In muscle contraction, what causes the actin filaments to slide toward the M line?

    <p>Conformational change in the myosin head</p> Signup and view all the answers

    What is the purpose of the troponin-tropomyosin complex in muscle contraction?

    <p>Lifting tropomyosin off active sites on actin filaments</p> Signup and view all the answers

    Where does the energy that powers the power stroke in muscle contraction come from?

    <p>Stored ADP</p> Signup and view all the answers

    What initiates muscle action by lifting tropomyosin off active sites on actin filaments according to the Sliding Filament Model?

    <p>Binding of calcium ions to troponin</p> Signup and view all the answers

    Which type of muscle fiber is best suited for long-distance running or cycling?

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

    What happens to calcium ions during muscle relaxation?

    <p>Calcium is pumped out of the sarcoplasm to the sarcoplasmic reticulum</p> Signup and view all the answers

    Which of the following is true about Type IIb muscle fibers?

    <p>They have fast contractile speed and high anaerobic capacity</p> Signup and view all the answers

    What is the approximate contractile speed of Type I muscle fibers?

    <p>110 ms</p> Signup and view all the answers

    How many muscle fibers are typically innervated by a single motor neuron for Type IIa fibers?

    <p>300-800</p> Signup and view all the answers

    What is the primary function of Type IIa muscle fibers?

    <p>Moderate-intensity activities requiring both aerobic and anaerobic metabolism</p> Signup and view all the answers

    What is the primary function of the Troponin complex within the thin filament?

    <p>Regulates the concentration of calcium ions in the muscle fiber</p> Signup and view all the answers

    What component of a myosin filament serves as an ATPase enzyme?

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

    Which of the following is true about Type IIb muscle fibers?

    <p>High anaerobic capacity and low aerobic capacity</p> Signup and view all the answers

    What is the main role of the Elasticity property of muscles?

    <p>Returning to original shape after being stretched or contracted</p> Signup and view all the answers

    What causes actin filaments to slide toward the M line during muscle contraction?

    <p>Binding of myosin heads to actin</p> Signup and view all the answers

    What distinguishes smooth muscles from skeletal muscles?

    <p>Involuntary control and non-striated appearance</p> Signup and view all the answers

    What is the primary role of the $t$-tubules in a muscle fiber?

    <p>To carry the depolarization from action potentials to the interior of the fiber</p> Signup and view all the answers

    Which protein makes up the thick filament in a sarcomere responsible for muscle contraction?

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

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

    <p>To store and release calcium ions for muscle contraction</p> Signup and view all the answers

    What is the primary function of the myofilaments in muscle contraction?

    <p>To interact and slide past each other, generating the force for muscle contraction</p> Signup and view all the answers

    Which type of muscle fiber is better suited for explosive activities?

    <p>Type IIb (fast-twitch) muscle fibers</p> Signup and view all the answers

    What is the primary role of the light chain on a myosin molecule?

    <p>To act as an ATPase enzyme, powering the contraction process</p> Signup and view all the answers

    What is the primary function of the sarcoplasmic reticulum in a muscle fiber?

    <p>To store and release calcium ions for muscle contraction</p> Signup and view all the answers

    What is the primary role of the t-tubules in a muscle fiber?

    <p>To allow for rapid transmission of the action potential into the cell</p> Signup and view all the answers

    According to the Sliding Filament Model, what causes the actin filaments to slide toward the M line during muscle contraction?

    <p>The binding of myosin heads to actin filaments and the power stroke</p> Signup and view all the answers

    What is the primary function of the troponin complex within the thin filament?

    <p>To regulate the interaction between actin and myosin during muscle contraction</p> Signup and view all the answers

    What is the primary function of the myosin heads within the thick filament?

    <p>To bind to actin filaments and undergo a power stroke during muscle contraction</p> Signup and view all the answers

    What is the immediate result of the cleavage of ATP by ATPase in muscle contraction?

    <p>The release of energy for the power stroke</p> Signup and view all the answers

    What is the main difference between Type I and Type II muscle fibers?

    <p>Type I fibers have high aerobic endurance, while Type II fibers are better for anaerobic or explosive activities.</p> Signup and view all the answers

    Which type of muscle fiber has a high anaerobic capacity and motor unit strength?

    <p>Type IIb muscle fibers</p> Signup and view all the answers

    What is a characteristic of Type IIa muscle fibers compared to Type I and Type IIb fibers?

    <p>Type IIa fibers have moderate aerobic capacity and fatigue resistance.</p> Signup and view all the answers

    Which statement best describes the function of Type IIb muscle fibers?

    <p>Low aerobic capacity and fatigue resistance</p> Signup and view all the answers

    In terms of the sarcoplasmic reticulum, how do Type IIa muscle fibers differ from Type I muscle fibers?

    <p>Type IIa muscles store more calcium in the sarcoplasmic reticulum compared to Type I muscles.</p> Signup and view all the answers

    What differentiates Type IIa muscle fibers from Type IIb muscle fibers?

    <p>Mitochondrial density</p> Signup and view all the answers

    What is the role of ATP in the initial stages of muscle contraction according to the Sliding Filament Model?

    <p>ATP is cleaved by ATPase, energizing the myosin heads in a 'cocked' position</p> Signup and view all the answers

    What is the primary function of the troponin-tropomyosin complex during muscle contraction?

    <p>To cover and uncover the active sites on actin filaments</p> Signup and view all the answers

    What is the primary source of energy that powers the 'power stroke' during muscle contraction?

    <p>The stored energy from the 'cocked' myosin head conformation</p> Signup and view all the answers

    What is the primary event that initiates the muscle contraction process?

    <p>Release of calcium ions from the sarcoplasmic reticulum</p> Signup and view all the answers

    What is the primary result of the 'power stroke' during muscle contraction?

    <p>The actin filaments slide toward the M line</p> Signup and view all the answers

    What is the primary function of the ATPase enzyme on the myosin heads?

    <p>To cleave ATP, energizing the myosin heads</p> Signup and view all the answers

    Study Notes

    Muscle Structure and Function

    • A muscle fiber is enclosed by a plasma membrane called the sarcolemma.
    • The sarcoplasmic reticulum (SR) is a specialized organelle responsible for storing, releasing, and reuptake ion calcium.
    • T-tubules allow for rapid transmission of the action potential into the cell and play an important role in regulating cellular calcium concentration.

    Myofibril Structure

    • Myofibrils are made up of sarcomeres, the smallest functional units of a muscle.
    • A sarcomere is composed of filaments of two proteins, myosin and actin, which are responsible for muscle contraction.
    • Myosin is a thick filament with a globular head at one end.
    • An actin filament is composed of actin, tropomyosin, and troponin. It is attached to a Z disk.

    Muscle Contraction

    • Action potential is a rapid change in membrane potential that travels rapidly along the membrane.
    • It is caused by the inflow of Na+ (highly concentrated outside the cell) and the outflow of K+ (highly concentrated inside the cell), causing a change in the voltage of the cell, producing a spike in the action potential.

    The Sliding Filament Model

    • Proposed in the early 1950s by two British biologists, Hugh Huxley and Andrew Huxley.
    • The theory proposes that a muscle shortens or lengthens because thick and thin filaments slide over each other without changing length.

    Muscle Fiber Action

    • Muscle action is initiated by a nerve impulse.
    • If the cell receives the right stimulus, an action potential occurs, which releases stored Ca2+ ions.
    • Ca2+ ions bind with troponin, which lifts the tropomyosin molecules off the active sites on the actin filament.
    • These open sites allow the myosin heads to bind to them.
    • Energy for muscle action is provided when the myosin head binds to ATP.
    • ATPase on the myosin head splits the ATP into a usable energy source.

    Muscle Fiber Types

    • Type I (Red) fibers: have high aerobic endurance and are suited to low-intensity endurance activities.
    • Type II (White) fibers: are better for anaerobic or explosive activities.
    • Type IIa fibers: are mixed oxidative-glycolytic fibers.
    • Type IIb fibers: are glycolytic fibers.

    Muscle Properties

    • Contractility: the ability to contract or shorten, allowing muscles to generate tension.
    • Extensibility: the property of muscles that allows them to be stretched or lengthened beyond their resting length.
    • Elasticity: the ability to return to its original shape after being stretched or contracted.
    • Excitability: the capacity to receive and respond to stimuli (from the motor neuron, neurotransmitters, hormone, etc).

    Muscle Types

    • Skeletal muscle: primary function is to enable movement of the body; attached to the bones of the skeleton.
    • Smooth muscle: involuntary muscle; controlled unconsciously; found in the walls of blood vessels and internal organs.
    • Cardiac muscle: controls itself with help from nervous and endocrine systems; only found in the heart.### Myofilaments
    • Myofilaments are responsible for muscle contraction
    • Thin filaments consist of Actin, Troponin complex, and Tropomyosin
    • Thick filaments consist of Myosin molecules, with a tail and two globular heads that can bind both ATP and Actin
    • Myosin heads function as an ATPase enzyme, using ATP as an energy source for contraction

    Actin Filament (Thin Filament)

    • Composed of ACTIN, TROPOMYOSIN, and TROPONIN COMPLEX
    • 2 helical strands of actin protein intertwined with 2 helical strands of tropomyosin protein
    • Troponin complex consists of three globular protein subunits (C, I, and T)
    • TnC binds calcium, TnI is inhibitory, and TnT binds tropomyosin

    Organelles of the Muscle Cell (Fiber)

    • MITOCHONDRIA: Power plant of ATP, provides myofibrils with large amounts of energy for muscle contraction
    • SARCOPLASMIC RETICULUM: Specialized endoplasmic reticulum, regulates calcium storage, release, and reuptake, important for muscle contraction

    Muscle Fiber

    • Surrounded by layers of connective tissue (epimysium, perimysium, and endomysium) for strength and stability

    Muscle Fiber Action

    • Muscle contraction occurs when myosin binds with actin, causing actin filaments to slide across each other
    • Muscle action ends when calcium is pumped out of the sarcoplasm to the sarcoplasmic reticulum for storage

    Types of Muscle Fibers

    • Skeletal muscles contain both Type I and Type II fibers
    • Type I (Red): High aerobic endurance, suited for low-intensity endurance activities
    • Type II (White): Better for anaerobic or explosive activities, divided into Type IIa and Type IIb

    Type I Muscle Fibers

    • Oxidative Fiber, high aerobic capacity and fatigue resistance
    • Rich in mitochondria, slow contractile speed (110 ms)
    • Found in muscles with slow, prolonged activity, 10–180 fibers per motor neuron

    Type IIa Muscle Fibers

    • Mixed oxidative-glycolytic fiber, moderate aerobic capacity and fatigue resistance
    • High anaerobic capacity, fast contractile speed (50 ms)
    • Highly developed sarcoplasmic reticulum, 300–800 fibers per motor neuron

    Type IIb Muscle Fibers

    • Glycolytic Fiber, low aerobic capacity and fatigue resistance
    • High anaerobic capacity and motor unit strength, fast contractile speed (50 ms)
    • Highly developed sarcoplasmic reticulum, 300–800 fibers per motor neuron

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