Chapter 6: The Muscular System

Presented by Patty Bostwick-Taylor, Florence Darlington Technical College

Overview

• Muscles enable all body movements.
• Three basic types of muscle:
  1. Skeletal Muscle
  2. Cardiac Muscle
  3. Smooth Muscle

Muscle Types

Skeletal Muscle

• Attached to bones by tendons.
• Characteristics:
  • Large, cigar-shaped, multinucleate.
  • Striated and voluntary.
• Structure:
  • Endomysium encloses a single muscle fiber.
  • Perimysium wraps a fascicle (bundle).
  • Epimysium covers the entire muscle.
  • Fascia is outside the epimysium.
• Attachments:
  • Tendons: Cordlike, mostly collagen fibers.
  • Aponeuroses: Sheetlike, attach muscles indirectly.

Smooth Muscle

• No striations, involuntary.
• Found in walls of hollow organs.
• Spindle-shaped, uninucleate.
• Slow, sustained contractions.

Cardiac Muscle

• Striated, involuntary, found only in heart walls.
• Uninucleate, joined by intercalated discs.
• Contracts at a steady rate set by pacemaker.

Muscle Functions

• Movement, posture, supporting organs, stabilizing joints, and generating heat.

Microscopic Anatomy of Skeletal Muscle

• Sarcolemma: Specialized plasma membrane.
• Myofibrils: Long organelles with segments called sarcomeres.
• Muscle contraction facilitated by microfilaments.
• Sarcomere: Contractile unit, consists of myofilaments (actin and myosin).

Myofilaments

• Thick Filaments: Composed of myosin with ATPase enzymes; form cross bridges during contraction.
• Thin Filaments: Composed of actin; anchored to Z disc; overlap with myosin during contraction.
• Sarcoplasmic Reticulum (SR): Stores/releases calcium, crucial for contraction.

Stimulation and Contraction of Skeletal Muscle

• Irritability: Ability to respond to stimuli.
• Contractility: Ability to shorten forcibly.
• Extensibility and Elasticity: Ability to stretch and recoil.

Nerve Stimulus and Action Potential

• Skeletal muscles require stimulation by motor neurons.
• Neuromuscular Junction: Site of nerve-muscle communication.
• Acetylcholine (ACh): Neurotransmitter that triggers muscle contraction.
• Action Potential: Electrical impulse conducing muscle contraction.

Mechanism of Muscle Contraction: Sliding Filament Theory

• Calcium ions facilitate cross-bridge formation.
• ATP provides energy for myosin movement along actin.
• Contraction shortens muscle fiber.

Contraction of Skeletal Muscle as a Whole

• Graded Responses: Varying contraction degrees.
• Responses influenced by stimulation frequency and number of muscle cells involved.

Types of Muscle Contraction

• Isotonic: Muscle shortens, movement occurs.
• Isometric: Tension increases without muscle shortening (e.g., pushing against immovable object).

Energy for Muscle Contraction

• ATP: Primary energy source.
• Regeneration pathways:
  1. Direct phosphorylation by creatine phosphate
  2. Aerobic pathway
  3. Anaerobic glycolysis

Muscle Fatigue and Oxygen Deficit

• Fatigue arises from ion imbalances, lactic acid buildup, and ATP depletion.
• Oxygen debt repaid post-exercise.

Effects of Exercise on Muscles

• Aerobic Exercise: Enhances endurance and muscle flexibility.
• Resistance Exercise: Increases muscle size and strength.

Muscle Movements, Roles, and Names

• Origin: Attachment to less movable bone.
• Insertion: Attachment to movable bone.
• Prime Mover: Main muscle responsible for movement.
• Antagonist: Muscle opposing prime mover.
• Synergist: Aids prime mover, stabilizes movement.

Naming Skeletal Muscles

• Based on direction, size, location, origins, shape, and action.

Developmental Aspects of the Muscular System

• Muscle control improves with nervous system maturation.
• Regular exercise maintains muscle health, prevents atrophy.
• Muscle mass decreases with age but can be preserved through exercise.