Muscular System

Muscular System Overview

• Types of Muscle:

  • Skeletal, Smooth, and Cardiac muscle.

Key Concepts in Muscle Behavior

• Myostatin:

  • Controls muscle growth; mutations lead to increased muscle size and reduced fat.

  • Clinical interest in blocking myostatin to aid musculoskeletal disorders.

Muscle Fiber Structure

• Components:

  • Each muscle consists of skeletal muscle tissue, connective tissues, blood vessels, and neurons.

• Connective Tissues:

  • Fascia: covers and separates muscles.

  • Epimysium: surrounds entire muscle.

  • Perimysium: surrounds fascicles.

  • Endomysium: surrounds individual muscle fibers.

• Muscle Fibers:

  • Contain myofibrils made up of actin and myosin, resulting in striations.

Muscle Contraction

• Process:

  • Triggered by a nerve impulse releasing acetylcholine.

  • Myosin cross-bridges bind to actin, performing a pulling action;
    resulting in sarcomere shortening (shortening of the muscle fiber).

• Energy Sources:

  • ATP and Creatine Phosphate provide energy; glycolysis can occur anaerobically.

Oxygen Debt and Fatigue

• Oxygen Debt:

  • Occurs during strenuous exercise, leading to lactic acid accumulation.

• Muscle Fatigue:

  • Result from insufficient oxygen or energy source.

Neuromuscular Junction

• Connection Site:

  • Motor neurons stimulate muscle fibers to contract at the neuromuscular junction.

Types of Muscle Contractions

• Twitch vs. Sustained Contraction:

  • Twitch: brief contraction/relaxation cycle.

  • Tetanic Contraction: continuous, strong contraction due to rapid stimuli.

Smooth and Cardiac Muscle

• Smooth Muscle:

  • Involuntary; lacks striations; uses acetylcholine and norepinephrine for contraction.

• Cardiac Muscle:

  • Striated, involuntary, and self-exciting due to intercalated discs that allow rapid impulse transmission.

Skeletal Muscle Actions

• Prime Movers:

  • Main muscle responsible for a movement.

• Synergists:

  • Assist prime movers and help steady movements.

• Antagonists:

  • Resist the action of prime movers, providing balance.

Major Skeletal Muscles and Functions

• Facial Muscles:

  • Include epicranius, orbicularis oculi, and zygomaticus for expression.

• Muscles of Mastication:

  • Masseter and temporalis for chewing.

• Pectoral Girdle and Arm Movement:

  • Muscles include trapezius, deltoid, and pectoralis major.

Additional Information

• Exercise Effects:

  • Regular resistance training can increase muscle size and strength, promote efficient metabolism, improve bone density, and enhance overall health.

Clinical Considerations

• Muscle Atrophy Prevention: Keeping muscles active even during bedridden states can minimize loss.