Muscle Physiology: Contraction and Types

Sep 10, 2024

Lecture: Muscle Physiology Part 3

Overview

  • Instructor: Professor Mariah Evans
  • Course: BSC 2085 - Human Anatomy and Physiology I
  • Lecture Focus: Muscles Part 3 (Part C)

Key Topics Discussed

Muscle Contraction Principles

  • Force of Muscle Contraction

    • Stronger stimulus leads to stronger contraction until the maximum is reached.
    • Motor units and size principle: Small, medium, and large motor units.
    • Recruitment principle: More motor units are recruited for bigger jobs.

  • Frequency and Trappe Effect

    • Faster stimulus application increases contractions.
    • Trappe effect: Successive stimuli lead to higher contractions before relaxation completes.

  • Degree of Muscle Stretch

    • Optimal force exerted when muscle is 80-120% of its normal length.

Factors Influencing Contraction

  • Muscle Fiber Types

    • Classification by speed: Slow and Fast.
    • By metabolic characteristics: Oxidative (aerobic) and Glycolytic (anaerobic).
    • Three fiber types: Slow oxidative, fast oxidative, fast glycolytic.
    • Fatigue Resistance: Slow oxidative fibers resist fatigue best.

  • Effects of Exercise

    • Aerobic Exercise: Increases capillaries, mitochondria, myoglobin. Improves endurance and fatigue resistance.
    • Resistance Exercise: Leads to muscle hypertrophy (increased size) and strength.
    • Overload Principle: Muscle strength increases with stress and tension.

Muscle Atrophy

  • Atrophy occurs with disuse; muscle strength can decline rapidly.
  • Lack of neural stimulation leads to significant muscle size reduction.

Types of Muscles

Skeletal Muscle

  • Voluntary, striated, requires neuromuscular junctions for contraction.

Smooth Muscle

  • Involuntary, lines hollow organs (except heart).
  • Structure: Longitudinal and circular layers.
  • Properties:
    • No neuromuscular junction; neurotransmitters released via varicosities.
    • Calcium binds to calmodulin instead of troponin.

Cardiac Muscle

  • Striated, involuntary, located in heart.

Smooth Muscle Characteristics

  • No striations, involuntary.
  • Lack of: T-tubules, neuromuscular junctions.
  • Calcium Regulation: Involves calmodulin (not troponin as in skeletal muscle).
  • Contraction: Slow, resistant to fatigue, self-excitatory.

Muscle Contraction Mechanism

  • Calcium's Role: Essential for contraction across all muscle types.
  • Actin and Myosin: Key proteins in contraction.

Regulation of Contractions

  • Influenced by neurotransmitters, hormones, and environmental factors (e.g., CO2 levels, pH).
  • Examples: Hyperventilation is regulated by CO2 levels; acidic blood pH can lead to cardiac arrest.

Muscle Growth: Hyperplasia and Hypertrophy

  • Hypertrophy: Increase in muscle size.
  • Hyperplasia: Increase in number of cells (smooth muscle capability).

Disorders: Muscular Dystrophy

  • Description: Progressive weakening of muscles.
  • Most Common: Duchenne muscular dystrophy, X-linked.
  • Symptoms: Muscle atrophy, respiratory failure.
  • Current Treatments: Prednisone, attempts at myoblast transfer, gene therapy.

Conclusion

  • Emphasized the importance of understanding muscle physiology for overall health and disease conditions.
  • Encouraged alternating aerobic and anaerobic exercises for optimal muscle health.

These notes summarize the lecture on muscle physiology, focusing on muscle contraction principles, fiber types, effects of exercise, and the comparison of muscle types, including skeletal, smooth, and cardiac muscle.