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Ch.9 Part 3

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Terms in this set (22)

  • Factors affecting force of muscle contraction

    Force depends on number of cross bridges attached, influenced by: 1) Number of muscle fibers stimulated (recruitment), 2) Relative size of fibers, 3) Frequency of stimulation, 4) Degree of muscle stretch (80-120% optimal).

  • Effect of muscle fiber recruitment on contraction force

    More motor units recruited leads to greater force of contraction due to increased number of muscle fibers activated.

  • Optimal sarcomere length for force generation

    Sarcomeres generate maximum force when stretched to 80-120% of resting length; less overlap or excessive stretch reduces force.

  • Muscle fiber types based on contraction speed and metabolism

    Three types: Slow oxidative (slow, aerobic), Fast oxidative (fast, aerobic), Fast glycolytic (fast, anaerobic glycolysis).

  • Characteristics of slow oxidative fibers

    Slow ATPase activity, aerobic metabolism, high myoglobin, fatigue-resistant, suited for endurance and posture maintenance.

  • Characteristics of fast glycolytic fibers

    Fast ATPase activity, anaerobic glycolysis, low myoglobin, fatigable, suited for short-term intense movements like hitting a baseball.

  • Effect of load on muscle contraction velocity and duration

    Greater load decreases contraction velocity and shortens duration; muscles contract fastest with no load.

  • Role of recruitment in contraction velocity and duration

    Increased recruitment of motor units results in faster and more prolonged muscle contractions.

  • Adaptations from aerobic (endurance) exercise

    Increased muscle capillaries, mitochondria, myoglobin; improves endurance, strength, fatigue resistance; may convert fast glycolytic to fast oxidative fibers.

  • Adaptations from resistance (anaerobic) exercise

    Muscle hypertrophy due to fiber size increase, more mitochondria, myofilaments, glycogen, connective tissue; increases muscle strength and size.

  • Disuse atrophy in muscles

    Muscle degeneration from immobilization or loss of neural stimulation; strength declines rapidly; fibrous tissue replaces muscle; rehabilitation may become impossible.

  • Location and organization of smooth muscle

    Found in walls of hollow organs (except heart); organized in sheets with longitudinal and circular layers oriented at right angles.

  • Differences between smooth and skeletal muscle fibers

    Smooth muscle fibers are spindle-shaped, single nucleus, no striations, lack connective tissue sheaths except endomysium, and have varicosities instead of neuromuscular junctions.

  • Role of varicosities in smooth muscle innervation

    Varicosities are bulbous nerve swellings that release neurotransmitters into wide synaptic clefts (diffuse junctions) to innervate smooth muscle.

  • Sources of Ca2+ for smooth muscle contraction

    Calcium enters mainly from extracellular fluid via caveolae and voltage-gated channels; some Ca2+ released from sarcoplasmic reticulum.

  • Structural features unique to smooth muscle fibers

    Myofilaments arranged diagonally, thick filaments fewer with heads along length, no troponin but calmodulin binds Ca2+, intermediate filaments and dense bodies anchor filaments.

  • Mechanism of smooth muscle contraction initiation

    Ca2+ binds calmodulin, activating myosin light chain kinase, which phosphorylates myosin heads to enable cross bridge formation with actin.

  • Steps to stop smooth muscle contraction

    Ca2+ detaches from calmodulin, Ca2+ actively transported out or into SR, and myosin is dephosphorylated to inactive form.

  • Energy efficiency of smooth muscle contraction

    Contracts and relaxes slowly, maintains prolonged contraction with low energy cost due to slower ATPases and myofilament latch mechanism.

  • Regulation of smooth muscle contraction

    Controlled by nerves, hormones, and local chemicals; neurotransmitters can stimulate or inhibit depending on receptor type; some smooth muscle cells self-excitatory.

  • Stress-relaxation response in smooth muscle

    Smooth muscle briefly responds to stretch then adapts, allowing organs to store contents and maintain function over large volume changes.

  • Types of smooth muscle

    Unitary (visceral) smooth muscle: electrically coupled, spontaneous action potentials; Multiunit smooth muscle: independent fibers, few gap junctions, controlled by autonomic nervous system.