Chapter 6: The Skeletal System and Muscle Tissue Overview

Functions of the Skeletal System

Support, Protection of organs, Movement (leverage for muscles), Mineral storage (Ca, P), Blood cell production (hematopoiesis), Triglyceride storage (yellow marrow)

Classification of Bones by Shape

Long (femur), Short (carpals), Flat (sternum), Irregular (vertebrae), Sesamoid (patella)

Classification of Bones by Internal Structure

Compact (dense outer layer), Spongy (trabecular, inner bone)

Osteogenic cells

Stem cells

Osteoblasts

Build bone

Osteocytes

Maintain bone

Osteoclasts

Break down bone

Matrix Composition - Organic

Collagen - tensile strength

Matrix Composition - Inorganic

Calcium phosphate - compression resistance

Compact Bone

Osteons, Central & perforating canals

Spongy Bone

Trabeculae, Red marrow in spaces

Ossification

Bone formation

Calcification

Deposition of calcium salts (can occur in tissues)

Endochondral Ossification

Bone replaces cartilage

Growth Types

Appositional (width), Interstitial (length)

Primary Center of Ossification

Diaphysis

Secondary Center of Ossification

Epiphysis

Epiphyseal Plate/Line

Growth region/closed growth line

Intramembranous Ossification

Bone from mesenchymal tissue (flat bones)

Vascular Supply of Bone

Nutrient arteries, Metaphyseal, epiphyseal, and periosteal vessels

Bone Remodeling & Homeostasis

Balance of osteoblast and osteoclast activity, Responds to stress, hormones, minerals

Factors Affecting Bone Development

Exercise: stimulates remodeling, Hormones: GH, calcitriol, PTH, calcitonin, sex hormones, Vitamins: A: osteoblast activity, B, C: collagen formation, D: calcium absorption, K: bone protein synthesis, Minerals: Ca and P crucial for matrix

Types of Fractures

Closed, open, comminuted, spiral, greenstick, etc.

Fracture Healing

Hematoma → soft callus → hard callus → remodeling

Osteopenia

Mild loss of bone mass

Osteoporosis

Severe, pathological bone loss

Functions of Skeletal Muscle

Movement, posture, support soft tissues, guard entrances/exits, heat production, nutrient reserves

Muscle Tissue Organization

Whole muscle → fascicle → fiber → myofibril → sarcomere

Skeletal Muscle Fiber Anatomy

Sarcolemma: membrane, Sarcoplasm: cytoplasm, Sarcoplasmic Reticulum: stores Ca²⁺, T-tubules: conduct action potential

Sarcomere Components

Z lines, M line, A band, I band, H zone, Actin (thin), myosin (thick)

Muscle Contraction Signals

Resting Membrane Potential: polarized muscle fiber, Action Potential: depolarization triggers contraction

Neuromuscular Junction (NMJ)

ACh: neurotransmitter released, AChE: breaks down ACh, Calcium: triggers actin-myosin interaction

Sliding Filament Model

Calcium binds to troponin → shifts tropomyosin → myosin binds → ATP powers the sliding

Muscle Contraction Types

Isotonic: movement (concentric vs eccentric), Isometric: no movement

Tension Patterns

Treppe: gradual increase, Summation: increasing force, Incomplete tetany: slight relaxation, Complete tetany: no relaxation

Energy Sources for Contraction

ATP, Creatine Phosphate (CP), Glycolysis (anaerobic): short-term, Aerobic respiration: long-term

Muscle Metabolism

Metabolic demand varies by activity level

Muscle Fatigue & Adaptation

Fatigue: due to low ATP, pH, Ca²⁺, Hypertrophy: muscle growth, Atrophy: loss from inactivity or aging

Muscle Fiber Types

Slow (Type I): fatigue-resistant, aerobic, Intermediate (Type IIa): mix of endurance/power, Fast (Type IIb): powerful, fatigue quickly

Skeletal vs Cardiac Muscle

Cardiac: intercalated discs, autorhythmic, branched, single nucleus

Skeletal vs Smooth Muscle

Smooth: no sarcomeres, spindle-shaped, involuntary, found in walls of organs/vessels