Skeletal System – Bone and Muscle

1. Introduction

• The skeletal system is the framework of the body, made up of bones, cartilage, ligaments, and joints.
• It provides support, protection, movement, storage, and blood cell production.
• An adult human body has 206 bones (children have more due to unfused bones).

2.Functions of Skeletal System

• Support → gives shape and structure to the body.

• Protection → vital organs (skull protects brain, rib cage protects heart & lungs).
• Movement → bones act as levers, joints allow motion with muscles.
• Hemopoiesis (Blood cell formation) → red bone marrow produces RBCs, WBCs, platelets.
• Storage → minerals (calcium, phosphorus) and fats (in yellow marrow).
• Endocrine Role → bone cells help regulate calcium metabolism via hormones.

3. Composition of Skeletal System

• Bones → rigid, strong structures.
• Cartilage → flexible connective tissue in joints, nose, ears, trachea.
• Ligaments → connect bone to bone.
• Tendons (supporting role though muscular system) → connect muscle to bone.
• Joints → sites where two or more bones meet.

4. Classification of Bones A. By Shape

1. Long Bones → femur, humerus (support, movement).
2. Short Bones → carpals, tarsals (stability, limited motion).
3. Flat Bones → skull, ribs, sternum (protection, muscle attachment).
4. Irregular Bones → vertebrae, facial bones (specialized functions).
5. Sesamoid Bones → patella (develop within tendons).
   B. By Location
   • Axial Skeleton (80 bones) → skull, vertebral column, rib cage.
   • Appendicular Skeleton (126 bones) → upper limbs, lower limbs, pectoral & pelvic girdles.

5. Divisions of Skeletal System A. Axial Skeleton (80 bones)

1. Skull (22 bones)
   • Cranial (8): frontal, parietal (2), temporal (2), occipital, sphenoid, ethmoid.
   • Facial (14): maxilla, mandible, zygomatic, nasal, lacrimal, palatine, vomer, inferior nasal conchae.
2. Hyoid Bone (1) → U-shaped, in neck, supports tongue.
3. Auditory Ossicles (6) → malleus, incus, stapes in each ear.
4. Vertebral Column (26 bones)
   • Cervical (7), Thoracic (12), Lumbar (5), Sacrum (1), Coccyx (1).
5. Thoracic Cage (25 bones)
   • Sternum (1), Ribs (24 → 12 pairs).
   B. Appendicular Skeleton (126 bones)
6. Pectoral Girdle (4 bones)
   • Clavicle (2), Scapula (2).
7. Upper Limbs (60 bones)
   • Arm: Humerus (2).
   • Forearm: Radius (2), Ulna (2).
   • Hand: Carpals (16), Metacarpals (10), Phalanges (28).
8. Pelvic Girdle (2 bones)
   • Hip bones (coxal bones).
9. Lower Limbs (60 bones)
   • Thigh: Femur (2), Patella (2).
   • Leg: Tibia (2), Fibula (2).
   • Foot: Tarsals (14), Metatarsals (10), Phalanges (28).

6. Structure of a Long Bone

6. Structure of a Long Bone
   • Diaphysis (shaft): central tubular region.
   • Epiphysis (ends): wider ends, contains spongy bone & red marrow.
   • Metaphysis: growth plate area.
   • Articular Cartilage: covers joints, reduces friction.
   • Periosteum: outer membrane, rich in blood vessels/nerves.
   • Medullary Cavity: central cavity with bone marrow.
   • Endosteum: inner lining membrane.
7. Microscopic Structure of Bone
   • Compact Bone (dense):
   • Made of osteons (Haversian systems).
   • Contains central canal, lamellae, osteocytes in lacunae, and canaliculi.
   • Spongy Bone (cancellous):
   • Trabeculae with spaces filled with red marrow.
   • Bone Cells:
   • Osteoblasts → build bone.
   • Osteoclasts → break down bone.
   • Osteocytes → mature bone cells.
   • Bone-lining cells → regulate mineral exchange.
8. Joints of Skeleton
   • Definition: Junction where 2 or more bones meet.
   • Classification by Structure:
   • Fibrous Joints: immovable (sutural joints of skull).
   • Cartilaginous Joints: slightly movable (intervertebral discs).
   • Synovial Joints: freely movable (knee, shoulder).
   • Classification by Movement:
   • Ball & Socket (hip, shoulder).
   • Hinge (elbow, knee).
   • Pivot (atlantoaxial joint).
   • Gliding (carpals, tarsals).
   • Saddle (thumb).
   • Condyloid (wrist).
9. Development & Growth of Bones
   • Ossification: Process of bone formation.
   • Intramembranous (flat bones like skull).
   • Endochondral (most bones via cartilage model).
   • Influences: hormones (growth hormone, sex hormones, calcitonin), nutrition (calcium, vitamin D, protein), physical activity.
10. Applied/Nursing Aspects
    • Common bone disorders:
    • Fractures (simple, compound).
    • Osteoporosis (reduced bone mass).
    • Rickets/Osteomalacia (vitamin D deficiency).
    • Arthritis (joint inflammation).
    • Scoliosis/Lordosis/Kyphosis (spinal curvatures).
    • Nursing Considerations:
    • Immobility management.
    • Pain and inflammation care.
    • Prevention of falls in elderly.
    • Patient education about diet and exercise.
11. Summary for Quick Review
    • Skeleton = 206 bones.
    • Two divisions: Axial (80), Appendicular (126).
    • Functions = Support, Protection, Movement, Blood cell formation, Storage.
    • Types of bones = Long, Short, Flat, Irregular, Sesamoid.
    • Joints = Fibrous, Cartilaginous, Synovial.
    • Bone health requires nutrition, hormones, and physical activity.