Physiology of Muscles Overview

Physiology of Muscles

• Muscles are classified as skeletal, cardiac, and smooth muscle
• Skeletal muscle is voluntary, controlled consciously, and connects to bones for movement
• Cardiac muscle is involuntary, controlled by the autonomic nervous system, and has pacemaker cells
• Smooth muscle is involuntary, found in hollow organs, and regulates the movement of contents through the lumen

Muscle Functions and Properties

• Functions: Muscles cause movement, maintain posture, support internal organs, control openings (sphincters), and move contents through tubes (peristalsis)
• Properties:
  • Excitability (respond to stimuli)
  • Contractility (shorten and generate force)
  • Extensibility (stretch without damage)
  • Elasticity (return to original shape)
  • Conductivity (conduct electrical impulses)

Muscle Structure

• Skeletal muscles are composed of muscle fibers bundled into fascicles
• T-tubules conduct impulses into fibers
• Sarcoplasmic reticulum stores and releases calcium for contraction
• Myofibrils contain actin (thin) and myosin (thick) filaments

Muscle Contraction

• Sarcomere: Basic contractile unit of a muscle cell
• Sliding filament theory: Actin and myosin filaments slide past each other during contraction, creating muscle shortening
• Neuromuscular Junction, Sliding Filament Theory, Contraction of Motor Units, are studied in lab work
• Types of muscle contraction: Isotonic (change in length under constant tension) and isometric (increase in tension without change in length)
• Muscle tone is the baseline tension that maintains posture and readiness
• Motor unit is a single motor neuron and the muscle fibers it controls

Muscle Fatigue

• Tetanus is a sustained muscle contraction caused by rapid stimulation
• Muscular work involves ATP-powered cycles of contraction and relaxation. Prolonged work leads to fatigue and oxygen debt.
• Muscle fatigue results from depletion of energy reserves (ATP, glycogen), accumulation of lactic acid, or impaired calcium release.

Muscle Fiber Types

• Type I (slow-twitch, red): fatigue-resistant, efficient in low-intensity activity
• Type IIa (fast oxidative): moderately resistant to fatigue
• Type IIb/IIx (fast glycolytic): powerful but fatigue quickly

Muscle Training

• Regular exercise increases muscle size, strength, endurance, and resistance to fatigue, and enhances overall metabolism, circulation, and lung efficiency

Muscle Proprioceptors

• Muscle spindles detect muscle length and changes in length
• Golgi tendon organs detect tension and protect muscles from excessive force
• Joint receptors provide information about joint angle and motion