Human Skeletal System

Skeletal System

• Provides protection, support, movement, storage, and hematopoiesis (blood cell formation)
• Composed of five types of bones: flat, long, short, irregular, and sesamoid bones

Structure of a Long Bone

• Consists of proximal epiphysis, diaphysis (shaft), and distal epiphysis

Axial and Appendicular Skeleton

• Axial skeleton: contains the skull, vertebral column, and rib cage (80 bones)
• Appendicular skeleton: contains the limbs and pelvic bone (126 bones)

Muscular System

• Functions: movement, protection/support of organs and soft tissue, maintaining body temperature, and forming sphincters
• Consists of muscle fibers, which are composed of multiple myofibrils

Structure of Muscle Fiber

• Each myofibril has repeating sections called sarcomeres
• Sarcomeres consist of thin (actin) and thick (myosin) filaments, responsible for muscle contraction

Structure of Muscle as an Organ

• Composed of epimysium (dense irregular connective tissue), perimysium (dense irregular connective tissue), and endomysium (areolar connective tissue)

Tendons and Aponeurosis

• Tendons: cord-like structures of dense regular connective tissue
• Aponeurosis: thin, flattened sheets of dense irregular connective tissue

Types of Muscle Fibers

• Fast twitch fibers: rapid, powerful contractions, low endurance
• Slow twitch fibers: slow, less powerful contractions, high endurance
• Intermediate fibers: combination of fast and slow twitch fibers

Muscle Fiber Characteristics

• Slow oxidative fibers: slow, less powerful contractions, high endurance, red color, many mitochondria
• Fast oxidative fibers: fast, powerful contractions, intermediate size, light red color, aerobic respiration
• Fast glycolytic fibers: fast, powerful contractions, largest size, white color, anaerobic respiration

Muscle Metabolism

• Aerobic metabolism: uses oxygen, occurs in mitochondria, produces 34 ATP
• Anaerobic metabolism: no oxygen, occurs in cytoplasm, produces 2 ATP
• Creatine phosphate: high-energy molecule
• ATP, creatine phosphate, and glycogen storage: sources of energy for muscle contraction

Muscle Contraction

• Twitch: single muscle contraction
• Wave summation: rapid, repeated muscle contractions
• Tetanus: sustained muscle contraction, caused by neurotoxin of anaerobic bacteria (e.g., puncture wound)