6.3 Skeletal muscles
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Flashcards in this deck (36)

  • How do muscles contract?

    They work in antagonistic pairs; one muscle (agonist) contracts while the other (antagonist) relaxes.

    biology muscle_contraction

  • What advantage do antagonistic muscle pairs provide?

    They allow for reversal of movement and help maintain posture.

    biology muscle_function

  • What is the basic structure of skeletal muscle?

    Made of bundles of muscle fibers attached to bones by tendons.

    biology muscle_structure

  • What does a muscle fiber contain?

    • Sarcolemma
    • Sarcoplasm
    • Multiple nuclei
    • Myofibrils
    • Mitochondria
    • Sarcoplasmic reticulum
    biology muscle_fiber_structure

  • What is the function of the T tubules in muscle fibers?

    They are invaginations of the sarcolemma that help transmit signals to contract muscles.

    biology muscle_function

  • What role do calcium ions play in muscle contraction?

    They trigger the interaction between actin and myosin filaments.

    biology muscle_contraction calcium

  • What is the function of phosphocreatine in muscles?

    It provides a quick source of energy during contractions.

    biology energy muscle_metabolism

  • What are myofibrils?

    They are structures within muscle fibers, composed of repeating units called sarcomeres.

    biology muscle_structure myofibrils

  • What are the two types of filaments in a myofibril?

    • Myosin: thick filament
    • Actin: thin filament
    biology muscle

  • What structure units are myofibrils arranged in?

    • Sarcomeres
    • Z-line / disc at ends
    • M-line in middle
    • H zone contains only myosin
    biology muscle

  • What do I-bands and A-bands represent in myofibrils?

    • I-bands: light bands with thin actin filaments
    • A-bands: dark bands with thick myosin filaments
    biology muscle

  • What happens to the H zone during muscle contraction?

    The H zone gets shorter as myosin heads slide actin along myosin.

    biology muscle contraction

  • How does muscle contraction occur?

    Myosin heads slide actin, causing sarcomeres to contract and Z lines to get closer.

    biology muscle contraction

  • What remains unchanged during muscle contraction?

    A band stays the same length.

    biology muscle contraction

  • What does the H zone contain?

    Only myosin filaments.

    biology muscle

  • Describe the overall effect of simultaneous contraction of many sarcomeres.

    Contraction of myofibrils and muscle fibers as a whole.

    biology muscle contraction

  • What structural components are visible in a sarcomere diagram?

    • Thick myosin filament
    • Thin actin filament
    • Z disc
    • H zone
    • M line
    • I band
    • A band
    biology muscle

  • What initiates the release of calcium ions (Ca²+) during muscle contraction?

    Depolarisation spreads down the sarcolemma via T tubules, causing Ca²+ release from the sarcoplasmic reticulum.

    muscle_contraction calcium

  • How do calcium ions affect tropomyosin during contraction?

    Calcium ions bind to tropomyosin, causing it to move and expose binding sites on actin.

    muscle_contraction tropomyosin

  • What forms when myosin heads bind to exposed sites on actin?

    An actinomyosin crossbridge is formed.

    muscle_contraction actin

  • What role does ATP play in the reattachment of myosin heads?

    New ATP binds to myosin head, causing it to detach from the binding site.

    muscle_contraction atp

  • How does ATP hydrolysis contribute to muscle contraction?

    Hydrolysis releases energy for myosin heads to return to their original position.

    muscle_contraction atp

  • What happens to Ca²+ during muscle relaxation?

    Ca²+ is actively transported back into the endoplasmic reticulum using ATP energy.

    muscle_relaxation calcium

  • What does tropomyosin do during muscle relaxation?

    Tropomyosin moves back to block the myosin binding site on actin.

    muscle_relaxation tropomyosin

  • What energy source is critical for the cross-bridge cycling process?

    ATP is essential for continuing the cross-bridge cycle as long as Ca²+ is present.

    muscle_contraction atp

  • Describe the cross-bridge cycle visually in muscle contraction.

    Diagram illustrating the cross-bridge cycle in muscle contraction, showing the interaction between actin, myosin head, tropomyosin, and Ca2+ ions, powered by ATP hydrolysis

    muscle_contraction diagram

  • What is the role of phosphocreatine in muscle contraction?

    It rapidly phosphorylates ADP to regenerate ATP: \(ADP + ext{phosphocreatine} ightarrow ATP + ext{creatine}\)

    biology muscle_contraction

  • What type of respiration does slow twitch muscle fiber primarily utilize?

    Predominantly aerobic respiration to produce ATP.

    biology muscle_fibers

  • Where are slow twitch muscle fibers primarily located?

    In muscles used for posture, e.g., back and calves.

    biology muscle_fibers

  • Which muscle fiber type specializes in brief, intensive contractions?

    Fast twitch muscle fibers specialize in this activity.

    biology muscle_fibers

  • What causes fast twitch muscle fibers to fatigue quickly?

    High lactate concentration from rapid anaerobic respiration.

    biology muscle_fibers

  • List structures that contribute to the efficiency of slow twitch muscle fibers.

    • High myoglobin concentration
    • Many mitochondria
    • Abundant capillaries
    biology muscle_fibers

  • Identify a common mistake regarding the A band and H zone.

    Confusing the A band (contains myosin and actin) with the H zone (only myosin).

    biology exam_insights

  • What is a key property of fast twitch muscle fibers?

    They contain large quantities of glycogen for quick energy.

    biology muscle_fibers

  • What is the output of the reaction involving phosphocreatine?

    ATP and creatine are produced.

    biology muscle_contraction

  • What is the predominant fluid source in slow twitch muscle fibers?

    They have a high concentration of myoglobin for oxygen storage.

    biology muscle_fibers
Study Notes

Muscle Function and Structure

How Muscles Work

  • Muscles operate in antagonistic pairs, e.g., biceps/triceps.
    • One muscle acts as the agonist, contracting to create movement.
    • The opposing muscle serves as the antagonist, relaxing.
  • The skeleton is incompressible, allowing muscles to effectively transmit force to bones.

Structural Components of Skeletal Muscle

  • Composed of bundles of muscle fibers attached to bones via tendons.
  • Each muscle fiber consists of:
    • Sarcolemma: Membrane with inward folds (T tubules).
    • Sarcoplasm: Cytoplasm of muscle cells.
    • Multiple nuclei and numerous myofibrils.
    • High density of mitochondria and a sarcoplasmic reticulum.

Myofibril Structure

Ultrastructure of Myofibrils

  • Composed of two types of protein filaments:
    • Myosin (thick) and Actin (thin).
  • Organized into sarcomeres, which include:
    • Z-line: Boundaries of sarcomeres.
    • M-line: Center of the sarcomere.
    • H zone: Area with only myosin filaments.

Diagram showing the structure of a sarcomere, including thick and thin filaments

Banding Patterns in Myofibrils

Banding Patterns

  • I-bands: Light bands with only thin actin filaments.
  • A-bands: Dark bands with thick myosin filament presence; overlap with actin.
    • H zone: Contains only myosin.

Diagram showing the banding pattern of a sarcomere

Overview of Muscle Contraction

Muscle Contraction Mechanism

  • Myosin heads slide actin, causing sarcomeres to contract:
    • Shortening of H zones and I bands.
    • A band remains the same.
    • Z lines move closer.

Key Roles in Contraction

Roles of Key Molecules in Myofibril Contraction

Molecule Roles
Calcium Ions (Ca²+) Trigger contraction by interacting with tropomyosin and myofilaments.
Actin (A) Serves as the thin filament that myosin pulls during contraction.
Tropomyosin (T) Blocks actin binding sites; moves when Ca²+ binds to facilitate contraction.
Myosin (M) Thick filament that forms crossbridges with actin, enabling muscle contraction.
ATP Provides energy for myosin head movement and detachment.

Muscle Relaxation

Muscle Relaxation Process

  1. Ca²+ ions are actively transported back into the endoplasmic reticulum, requiring ATP.
  2. Tropomyosin re-blocks binding sites on actin, preventing further crossbridge formation.

Phosphocreatine in Muscle Contraction

Role of Phosphocreatine

  • Provides inorganic phosphate (Pi) for quick ATP regeneration:
    • Reaction: ADP + phosphocreatine → ATP + creatine.
  • Useful for short-term, intense exercise but depletes quickly.

Types of Skeletal Muscle Fibers

Slow vs. Fast Twitch Muscle Fibers

Property Slow Twitch Fast Twitch
Properties Endure long activities; aerobic ATP production; slow to fatigue. Suited for quick bursts; anaerobic ATP production; quick fatigue.
Location Predominantly in postural muscles (e.g., back). Found in muscles used for rapid movement (e.g., legs of sprinters).
Structure High myoglobin, many mitochondria, and capillaries. Lower myoglobin; high glycogen stores; rapid energy release.

Common Exam Mistakes

Common Mistakes in Answers

Mistake Clarification
Mixing A band and H zone A band contains overlapping actin & myosin; H zone has only myosin.
Overemphasis on troponin's role Not required in specification.
Confusion of binding sites Actin has binding sites, not active sites like enzymes.
Vague statements about actin movement Need to connect myosin action to actin movement.
Misunderstanding phosphocreatine's role Phosphocreatine yields Pi, not phosphorus.