Chapter 12- human physiology summarized

Overview of Muscle Types

• Human body contains 3 muscle types: skeletal, cardiac, and smooth
• Functions of muscles: generate motion, force, and heat; maintain homeostasis.
• Skeletal Muscle
• Attached to bones via tendons, enabling body movement
• Unique characteristics: striated (due to sarcomeres), multinucleated cells
• Functions: voluntary control, moving skeleton, maintaining body posture, generating heat through shivering

Organization of Skeletal Muscle

• Several levels of organization:
• Muscle organization: muscle > fascicle > muscle fiber > myofibril > sarcomere
• Fibers surrounded by connective tissue, grouped into fascicles.
• Each muscle fiber is composed of myofibrils (contractile units containing sarcomeres)

Muscle Fiber Anatomy

• Muscle fiber (cell) structure: long, cylindrical with many nuclei
• Sarcolemma (cell membrane), sarcoplasm (cytoplasm) containing organelles
• Myofibrils consist of thick (myosin) and thin (actin) filaments, arranged in sarcomeres

Muscle Contraction Process

• Sliding Filament Theory: explains contraction process
  • When a muscle contracts, myosin heads bind to actin, sliding past each other
  • Energy from ATP hydrolysis drives power stroke
• Excitation-Contraction Coupling:
  • Action potential leads to calcium release from sarcoplasmic reticulum
  • Calcium binds troponin, causing tropomyosin to shift and expose binding sites for myosin
  • Crossbridge cycling begins, resulting in muscle contraction

Control of Muscle Contraction

• Controlled by somatic motor neurons (skeletal muscle) via neuromuscular junction
• Action potential triggers calcium release affecting muscle contraction.

Summary of Muscle Physiology

• Each muscle fiber type has distinct characteristics in metabolism and fatigue resistance:
• Type I (Slow-twitch, oxidative): Endurance tasks, fatigue-resistant.
• Type II (Fast-twitch, glycolytic): Short burst high-intensity tasks, fatigue quickly.
• Mechanics of muscle action:
• Isometric contractions: tension without muscle shortening
• Isotonic contractions: muscle shortens and moves load
• Antagonistic muscle pairs: exert opposite effects, e.g., flexors v extensor

Smooth Muscle

• Types: visceral (single-unit) smooth muscle and multiunit smooth muscle
• Controlled by autonomic nervous system; less striated/uniform than skeletal muscle
• Contractions can be initiated by electrical or chemical signals.

Cardiac Muscle

• Properties: striated, branched, involuntary control, pacemaker potentials
• Cardiac muscle fibers are linked with intercalated discs, enabling synchronized contractions

Muscle Fatigue

• Caused by depletion of energy sources, accumulation of metabolic byproducts.
• Two main mechanisms: central (in brain) and peripheral (in muscle fibers) fatigue.
• Muscle fatigue has various causes and is vital to understand for improving training and performance.

Summary

• Muscle physiology integrates electrical signals, biochemical pathways, and mechanical properties for movement generation
• Regulated through multiple layers of control by the nervous system, with distinct roles for different muscle types
• Research in muscle physiology can lead to advancements in treatment for muscular disorders.