Muscle Types and Structure Quiz

Muscle Types

• Skeletal Muscle

  • Striated and voluntary.
  • Attached to bones via tendons.
  • Responsible for body movement and posture.
  • Multi-nucleated cells.

• Cardiac Muscle

  • Striated and involuntary.
  • Found exclusively in the heart.
  • Intercalated discs facilitate synchronized contraction.
  • Single nuclei per cell.

• Smooth Muscle

  • Non-striated and involuntary.
  • Found in walls of hollow organs (e.g., intestines, blood vessels).
  • Operates automatically, controlled by the autonomic nervous system.
  • Spindle-shaped cells with a single nuclei.

Muscle Structure

• Muscle Fiber

  • Basic contractile unit of muscle.
  • Composed of myofibrils, which contain actin and myosin filaments.
  • Surrounded by sarcolemma (cell membrane).

• Myofibrils

  • Long chains of sarcomeres (functional units).
  • Sarcomeres contain bands of actin (thin) and myosin (thick).
  • Arrangement leads to striations in skeletal and cardiac muscles.

• Connective Tissue

  • Epimysium: surrounds entire muscle.
  • Perimysium: surrounds bundles of muscle fibers (fascicles).
  • Endomysium: surrounds individual muscle fibers.
  • Helps in force transmission and protection.

Muscle Contraction

• Sliding Filament Theory

  • Actin and myosin filaments slide past each other, shortening the sarcomere.
  • Z-lines move closer together during contraction.

• Contraction Process

  1. Nerve Stimulation: An action potential from a motor neuron reaches the muscle fiber.
  2. Calcium Release: Calcium ions are released from the sarcoplasmic reticulum.
  3. Cross-Bridge Formation: Calcium binds to troponin, allowing myosin heads to attach to actin.
  4. Power Stroke: Myosin heads pivot, pulling actin filaments toward the center of the sarcomere.
  5. Relaxation: Calcium is reabsorbed, and muscle returns to resting state.

• Types of Contractions

  • Isometric: Muscle length remains the same while tension increases.
  • Isotonic: Muscle changes length while maintaining tension.
    • Concentric: Muscle shortens during contraction.
    • Eccentric: Muscle lengthens while under tension.

Muscle Types

• Skeletal Muscle: Striated and voluntary, responsible for body movement and posture; attached to bones via tendons.
• Cardiac Muscle: Striated and involuntary; found exclusively in the heart; intercalated discs facilitate synchronized contraction.
• Smooth Muscle: Non-striated and involuntary; found in walls of hollow organs; operates automatically, controlled by the autonomic nervous system.

Muscle Structure

• Muscle Fiber: Basic unit of muscle; composed of myofibrils which contain actin and myosin filaments.
• Myofibrils: Long chains of sarcomeres; sarcomeres contain bands of actin (thin) and myosin (thick); arrangement creates striations in skeletal and cardiac muscles.
• Connective Tissue:
  • Epimysium: surrounds entire muscle.
  • Perimysium: surrounds bundles of muscle fibers (fascicles).
  • Endomysium: surrounds individual muscle fibers.

Muscle Contraction

• Sliding Filament Theory: Actin and myosin filaments slide past each other, shortening the sarcomere.
• Contraction Process:
  • Nerve Stimulation: An action potential from a motor neuron reaches the muscle fiber.
  • Calcium Release: Calcium ions are released from the sarcoplasmic reticulum.
  • Cross-Bridge Formation: Calcium binds to troponin, enabling myosin heads to attach to actin.
  • Power Stroke: Myosin heads pivot, pulling actin filaments toward the center of the sarcomere.
  • Relaxation: Calcium is reabsorbed, and muscle returns to resting state.
• Types of Contractions:
  • Isometric: Muscle length remains the same while tension increases.
  • Isotonic: Muscle changes length while maintaining tension.
    • Concentric: Muscle shortens during contraction.
    • Eccentric: Muscle lengthens under tension.