Chapter 10: Anatomy and Physiology - Muscle Tissue

Introduction

• Muscle tissue is a primary tissue, one of the main tissues.
• Focus on skeletal muscle; cardiac and smooth muscle will be discussed in later chapters.
• Skeletal muscle is voluntary.
• Muscle tissue is specialized for contraction.

Types of Muscle

• Skeletal Muscle: Voluntary, moves body by pulling on bones.
• Cardiac Muscle: Involuntary, found in heart.
• Smooth Muscle: Found in hollow organs.

Functions of Skeletal Muscle

• Movement and posture maintenance.
• Supports soft tissues.
• Guards body entrances/exits.
• Maintains body temperature by burning energy.
• Stores nutrients.

Structure of Skeletal Muscle

• Contains muscle tissue and connective tissue.
• Rich blood supply for oxygen.
• Controlled by nerves.

Connective Tissue Layers in Skeletal Muscle

1. Epimysium: Outer layer of collagen fibers, separates muscle from surrounding tissues.
2. Perimysium: Surrounds muscle fiber bundles (fascicles).
3. Endomysium: Surrounds individual muscle cells (fibers).

Muscle Components

• Fascicles: Bundles of muscle fibers.
• Fibers: Individual muscle cells, multinucleate, striated.
• Sarcolemma: Muscle fiber membrane.
• Sarcoplasm: Cytoplasm of muscle fiber.

Muscle Fiber Anatomy

• Skeletal muscle fibers have T-tubules for transmitting action potentials.
• Sarcoplasmic reticulum surrounds myofibrils, stores calcium.
• Myofibrils contain myofilaments (thin and thick).

Myofilaments

• Thin Filaments (Actin): Contains F-actin, nebulin, tropomyosin, troponin.
• Thick Filaments (Myosin): Contains about 300 myosin molecules.

Sarcomere Structure

• Functional unit of muscle fiber.
• Includes A band, I band, H band, M line, Z lines.
• A Band: Contains thick filaments and zone of overlap.
• I Band: Contains thin filaments.
• Z Line: Boundary between sarcomeres.
• Titan: Elastic protein maintaining alignment.

Muscle Contraction: Sliding Filament Theory

• Contractile Process: Thin filaments slide toward center of sarcomere.
• Action Potential: Electrical impulse triggers contraction.
• Neuromuscular Junction: Connection between neuron and muscle fiber.

Steps for Muscle Contraction

1. Action potential arrives at neuromuscular junction.
2. Release of acetylcholine (ACh) into synaptic cleft.
3. ACh binds to receptors on sarcolemma.
4. Sodium channels open, sodium influx causes depolarization.
5. Action potential spreads via T-tubules.
6. Sarcoplasmic reticulum releases calcium.
7. Calcium binds to troponin, tropomyosin shifts, exposing active sites on actin.
8. Myosin heads bind to actin forming cross-bridges.
9. Power stroke: Myosin heads pull actin filaments, contracting the muscle.

Muscle Relaxation

• Calcium is reabsorbed, active sites on actin recovered, contraction ends.

Muscle Types and Properties

• Motor Unit: A motor neuron and the muscle fibers it controls.
• Muscle Tone: Normal tension in resting muscles.

Types of Muscle Contractions

• Isotonic: Muscle changes length (concentric and eccentric).
• Isometric: Muscle length remains constant.

Energy for Muscle Contraction

• Relies on ATP.
• Oxygen debt: Increased oxygen consumption post-exercise.

Muscle Fibers Types

• Fast Fibers: Quick, powerful, fatigues fast.
• Slow Fibers: Less powerful, greater endurance.
• Intermediate Fibers: Characteristics between fast and slow.

Factors Affecting Muscle Performance

• Hypertrophy: Muscle growth from training.
• Atrophy: Muscle reduction from inactivity.

Aging and Muscle Tissue

• Muscle fibers become smaller and less elastic.

Cardiac and Smooth Muscle Overview

• Cardiac Muscle: Involuntary, striated, found in heart, automaticity.
• Smooth Muscle: Found in organs, involuntary, non-striated.

This concludes Chapter 10 on muscle tissue anatomy and physiology.