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Muscle Tissue and Contraction - Anatomy & Physiology

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  • Types of muscle tissue

    The three types are skeletal, cardiac, and smooth muscle tissue.

  • Common properties of muscle tissue

    All muscle tissues share contractility, excitability, conductivity, distensibility, and elasticity.

  • Muscle cell plasma membrane and cytoplasm names

    The plasma membrane is the sarcolemma, and the cytoplasm is the sarcoplasm.

  • Components inside sarcoplasm

    The sarcoplasm contains myofibrils and the sarcoplasmic reticulum (SR).

  • Characteristics of skeletal muscle fibers

    Skeletal muscle fibers are long, striated, multinucleated, and voluntary muscle cells.

  • Function of T-tubules in skeletal muscle fibers

    T-tubules are inward extensions of the sarcolemma that surround myofibrils and help propagate action potentials.

  • Three types of myofilaments in muscle fibers

    Thick filaments (myosin), thin filaments (actin, troponin, tropomyosin), and elastic filaments (titin).

  • Cause of striations in skeletal muscle

    Striations result from the arrangement of myofilaments into I bands (thin filaments only) and A bands (overlapping thick and thin filaments).

  • Definition of a sarcomere

    The sarcomere is the functional unit of contraction, defined as the area between two Z-discs.

  • Sliding-filament mechanism

    Muscle contraction occurs as thick and thin filaments slide past each other, shortening the sarcomere.

  • Resting membrane potential of muscle fibers

    Muscle fibers at rest have a resting membrane potential of about \(-90\text{ mV}\).

  • Role of the Na+/K+ pump in muscle cells

    The Na+/K+ pump maintains ion gradients by pumping Na+ out and K+ in, contributing to the negative resting membrane potential.

  • Phases of an action potential in muscle fibers

    Depolarization: Na+ enters, making membrane potential more positive.
    Repolarization: K+ exits, restoring resting potential.

  • Components of the neuromuscular junction (NMJ)

    The NMJ includes the axon terminal, synaptic cleft, and motor end plate.

  • Excitation phase of muscle contraction

    ACh released from the axon terminal binds receptors on the motor end plate, producing an end-plate potential.

  • Excitation-contraction coupling

    The end-plate potential triggers an action potential that travels down T-tubules, causing Ca2+ release from the SR.

  • Role of Ca2+ in muscle contraction

    Ca2+ binds to troponin, causing tropomyosin to move and expose active sites on actin for myosin binding.

  • Crossbridge cycle in muscle contraction

    ATP hydrolysis cocks the myosin head, which binds actin and performs a power stroke, pulling actin toward the sarcomere center.

  • Muscle relaxation process

    ACh is broken down in the synaptic cleft, and Ca2+ is pumped back into the SR, ending contraction.

  • Immediate energy sources for muscle fibers

    Stored ATP and creatine phosphate provide immediate energy for muscle contraction.

  • Difference between glycolytic and oxidative catabolism

    Glycolytic catabolism is anaerobic ATP production in the cytosol; oxidative catabolism is aerobic ATP production in mitochondria.

  • Definition of a muscle twitch

    A twitch is a single contraction-relaxation cycle of a muscle fiber, including latent, contraction, and relaxation periods.

  • Difference between unfused and fused tetanus

    Unfused tetanus occurs with partial relaxation between stimuli; fused tetanus occurs with rapid stimuli causing sustained contraction.

  • Length-tension relationship in muscle fibers

    Maximal tension is produced when sarcomeres are at an optimal length before contraction.

  • Characteristics of Type I and Type II muscle fibers

    Type I fibers are slow-twitch, oxidative; Type II fibers are fast-twitch, glycolytic.

  • Definition of a motor unit

    A motor unit consists of one motor neuron and all the muscle fibers it innervates.

  • Muscle tone

    Muscle tone is the small, involuntary contractions of alternating motor units that maintain muscle readiness.

  • Types of muscle contractions

    Isotonic concentric (shortening), isotonic eccentric (lengthening), and isometric (no length change) contractions.

  • Smooth muscle contraction activation

    Ca2+ binds to calmodulin, activating myosin light-chain kinase (MLCK), which initiates crossbridge cycling.

  • Differences between smooth and skeletal muscle cells

    Smooth muscle cells are uninucleate, lack T-tubules and striations, and have less extensive SR than skeletal muscle fibers.

  • Types of smooth muscle tissue

    Single-unit smooth muscle contracts as a unit; multi-unit smooth muscle cells contract independently.

  • Cardiac muscle cell connections

    Cardiac muscle cells are joined by intercalated discs that allow physical and electrical coupling.