Skeletal Muscle and Mechanics of Body Movement

Introduction

This section introduces the structure and function of skeletal muscle, the types of muscle tissue, and the mechanics of body movement. Understanding these foundational concepts is essential for studying the musculoskeletal system in Anatomy & Physiology.

The Three Types of Muscle Tissue

Overview of Muscle Types

• Skeletal Muscle: Voluntary, striated muscle attached to bones, responsible for body movement.

• Cardiac Muscle: Involuntary, striated muscle found only in the heart, responsible for pumping blood.

• Smooth Muscle: Involuntary, non-striated muscle found in walls of hollow organs (e.g., intestines, blood vessels).

Antagonistic Muscles and Body Movement

Antagonistic Muscle Groups

Muscle groups that move bones in opposite directions are called antagonistic muscles. Muscles can only pull on bones; they cannot push.

• Flexion: Decreases the angle between bones (e.g., bending the elbow). The flexor contracts while the extensor relaxes.

• Extension: Increases the angle between bones (e.g., straightening the elbow). The extensor contracts while the flexor relaxes.

Example: During a biceps curl, the biceps brachii (flexor) contracts to flex the elbow, while the triceps brachii (extensor) relaxes. During extension, the triceps contracts and the biceps relaxes.

Structure of Skeletal Muscle

Muscle Fiber Organization

• Muscle fibers are the individual muscle cells, long and cylindrical, formed by the fusion of multiple cells and containing many nuclei.

• Satellite cells are stem cells that differentiate into muscle fibers for growth or repair.

• Muscle fibers are grouped into fascicles, which are bundles surrounded by connective tissue.

• The entire muscle is surrounded by connective tissue, which is continuous with the tendon that attaches muscle to bone.

Hierarchical Structure of Skeletal Muscle

• Muscle (organ) → Fascicle (bundle of fibers) → Muscle fiber (cell) → Myofibril (contractile element) → Sarcomere (functional unit)

• Connective tissue layers include the epimysium (surrounds muscle), perimysium (surrounds fascicles), and endomysium (surrounds individual fibers).

Example: The biceps brachii muscle is composed of many fascicles, each containing numerous muscle fibers, which in turn contain myofibrils made up of repeating sarcomeres.

Key Terms

• Tendon: Connective tissue that attaches muscle to bone.

• Fascicle: Bundle of muscle fibers within a muscle.

• Muscle fiber: Single muscle cell, multinucleated and elongated.

• Satellite cell: Muscle stem cell involved in growth and repair.

Additional info: The organization of skeletal muscle allows for efficient force transmission and repair. The presence of satellite cells is crucial for muscle regeneration after injury.