Chapter 10: Muscular Tissue

Overview

• Muscular tissue is responsible for motion through contraction and relaxation.
• Myology: Study of muscles.
• Three types of muscular tissue:
  • Smooth
  • Skeletal
  • Cardiac

Types of Muscular Tissue

Skeletal Muscle

• Characteristics:
  • Elongated, multinucleated, striated cells, unbranched.
  • Large diameter and length, contains sarcomeres.
  • Fast contraction, voluntary control by the somatic nervous system.
  • Limited regeneration.
• Functions: Movement, stabilize body positions.

Cardiac Muscle

• Characteristics:
  • Elongated, single nucleus, striated, branched.
  • Intercalated discs with gap junctions for unified contraction.
  • Moderate contraction speed, involuntary control by autonomic nervous system.
  • Limited regeneration.
• Location: Heart.

Smooth Muscle

• Characteristics:
  • Tapered, uninucleated, non-striated.
  • Small diameter and length, does not have sarcomeres.
  • Slow contraction, involuntary control by autonomic nervous system.
  • Considerable ability to regenerate compared to skeletal and cardiac muscles.
• Functions: Found in walls of hollow organs, erector pili in skin.

Functions of the Muscular System

• Produce body movements: Running, walking (skeletal muscles).
• Stabilize body positions: Sitting, standing (skeletal muscles).
• Move substances: Sphincters, smooth muscle in GI tract, urinary system.
• Thermogenesis: Generate heat through muscle contractions.

Characteristics of Muscle Tissue

• Excitable: Responds to stimuli, creates action potentials.
• Contractable: Shortens upon stimulation.
• Extensible: Can be stretched.
• Elastic: Returns to original shape after contraction.

Gross Anatomy of Skeletal Muscle

• Levels of Organization:
  • Chemical: Myofibrillar, actin and myosin proteins.
  • Cells: Muscle fibers.
  • Tissue: Muscle fascicles.
  • Organ: Whole muscle.
• Connective Tissue Components:
  • Tendons connect muscle to bone.
  • Deep fascia: Outer muscle covering.
  • Epimysium: Surrounds entire muscle.
  • Perimysium: Surrounds fascicles.
  • Endomysium: Surrounds individual muscle fibers.

Nervous System and Muscle Interaction

• Nerves stimulate muscles: Electrical impulses cause contraction.
• Somatic nervous system: Voluntary control for skeletal muscles.
• Autonomic nervous system: Involuntary control for smooth/cardiac muscles.

Blood Supply

• Muscles have abundant capillaries for nutrients, oxygen, and waste removal.
• High levels of ATP are crucial for contraction.

Microscopic Anatomy of Skeletal Muscle

• Muscle Fiber: Multinucleated, cylindrical, parallel cells.
• Myofibrils: Contain actin and myosin, form sarcomeres.
• Sarcoplasmic Reticulum: Stores/releases calcium ions.
• Sarcolemma: Plasma membrane with transverse tubules.
• Sarcoplasm: Cytoplasm with mitochondria for ATP, stores glycogen and myoglobin.

Sarcomere Structure

• Bands and Lines:
  • Z Discs: Separate sarcomeres.
  • I Band: Thin filaments only.
  • A Band: Thick filaments.
  • H Zone: Only thick filaments.
  • M Line: Middle, holds thick filaments.

Muscle Contraction and Relaxation

• Sliding Filament Model: Sarcomeres shorten as thin/thick filaments slide over each other.
• Contraction requires: ATP and calcium ions.
• Relaxation requires: Breakdown of acetylcholine, return of calcium to sarcoplasmic reticulum.

Motor Units and Neuromuscular Junctions

• Motor Unit: One motor neuron and all muscle fibers it stimulates.
• Neuromuscular Junction: Synapse between neuron and muscle fiber; involves acetylcholine.

Muscle Metabolism

• ATP Production:
  • Creatine phosphate system for short bursts.
  • Glycolysis: Anaerobic, produces lactic acid if no oxygen.
  • Aerobic respiration: Requires oxygen, produces 36 ATP.

Muscle Fatigue

• Causes include low calcium, depleted creatine phosphate, glycogen, ATP, insufficient oxygen, and lactic acid buildup.

Control of Muscle Tension

• Twitch vs. Tetanus: Single twitch vs. sustained contraction.
• Frequency of stimuli affects contraction force.
• Different muscles have varying refractory periods.

Types of Muscle Contractions

• Isometric, Concentric, Eccentric: Different types of workouts affect muscle tension and build.

Special Conditions

• Rigor Mortis: Post-mortem calcium leakage leads to muscle stiffness until tissue breakdown occurs.