Skeletal System: Structure, Function, and Organization Study Notes

Skeletal System

1. Bone Structure & Function

The skeletal system provides the framework for the human body, supporting movement, protecting organs, and serving as a reservoir for minerals and blood cell production.

• Support: Bones provide structural support for the entire body and a framework for the attachment of soft tissues and organs.

• Protection: Bones protect vital organs (e.g., the skull protects the brain, the rib cage protects the heart and lungs).

• Movement: Bones act as levers that muscles pull on to produce movement.

• Mineral Storage: Bones store minerals, primarily calcium and phosphorus, which can be released into the bloodstream as needed.

• Blood Cell Formation (Hematopoiesis): Red bone marrow produces red blood cells, white blood cells, and platelets.

2. Bone Tissue Types

Bones are composed of two main types of tissue, each with distinct structure and function.

• Compact Bone: Dense and solid, forming the outer layer of bones; provides strength for weight bearing.

• Spongy (Cancellous) Bone: Porous and lighter, found mainly at the ends of long bones and inside flat bones; contains red bone marrow.

3. Organization of the Skeletal System

The human skeleton is divided into two major divisions, each with specific components and functions.

Division	What it includes	Primary Function
Axial Skeleton	Skull, vertebral column, rib cage	Protection of central nervous system and vital organs
Appendicular Skeleton	Limb bones, pectoral and pelvic girdles	Movement and manipulation of environment

4. Total Bones

The adult human skeleton contains approximately 206 bones.

5. Axial Skeleton Labeling

The axial skeleton includes the following structures:

• Skull

• Cranial bones

• Facial bones

• Vertebral column

• Thoracic vertebrae

• Sacrum

• Coccyx

• Ribs

• Sternum

Main function: Protection (especially of the brain, spinal cord, and thoracic organs).

6. Appendicular Skeleton Labeling

The appendicular skeleton includes the bones of the limbs and girdles:

• Upper Limb & Girdle: Clavicle, scapula, humerus, radius, ulna, carpals, metacarpals, phalanges

• Lower Limb & Girdle: Coxal (hip) bone, femur, patella, tibia, fibula, tarsals, metatarsals, phalanges

7. Bone Classification Based on Shape

Bones are classified by shape, which relates to their function.

Bone Shape	Description	Example
Long	Longer than they are wide	Femur, humerus
Short	Cube-shaped	Carpals, tarsals
Flat	Thin, flattened, often curved	Sternum, skull bones
Irregular	Complex shapes	Vertebrae, hip bones
Sesamoid	Small, round, embedded in tendons	Patella

8. Anatomy of a Long Bone

Long bones have distinct anatomical regions:

• Diaphysis: Shaft of the bone

• Epiphysis: Ends of the bone

• Periosteum: Outer membrane covering the bone

• Medullary cavity: Central cavity containing yellow marrow

• Articular cartilage: Covers joint surfaces for smooth movement

• Epiphyseal plate/line: Site of bone growth in children/adolescents

Critical Thinking: The epiphyses are important for joint articulation and for the distribution of forces at the ends of long bones.

9. Joints

A. Definition

A joint (articulation) is a site where two or more bones meet, allowing for movement and flexibility.

B. Types of Joints by Structure

Joint Type	Description	Example
Fibrous	Connected by dense connective tissue; immovable	Sutures of the skull
Cartilaginous	Connected by cartilage; slightly movable	Intervertebral discs
Synovial	Joint cavity with synovial fluid; freely movable	Knee, shoulder

C. Types of Synovial Joints

• Hinge: Elbow

• Ball-and-socket: Shoulder, hip

• Pivot: Atlas and axis (neck)

• Gliding: Intercarpal joints

• Condyloid: Wrist

• Saddle: Thumb joint

10. Bone Remodeling Process

A. Key Cells

• Osteoclasts: Break down bone matrix, releasing minerals into the blood.

• Osteoblasts: Build new bone matrix.

• Osteocytes: Mature bone cells that maintain bone tissue.

B. Why Bone Remodeling Is Important

• Repairs micro-damage

• Regulates calcium levels

• Adapts bones to stress

• Prevents bone brittleness

11. Spine (Vertebral Column) Labeling

The vertebral column is divided into regions:

• Cervical vertebrae: 7

• Thoracic vertebrae: 12

• Lumbar vertebrae: 5

• Sacrum and Coccyx

12. Fracture Healing Process

Bone healing occurs in several stages:

1. Hematoma formation: Blood clot forms at the fracture site.

2. Fibrocartilaginous callus formation: Soft callus of collagen and cartilage forms.

3. Bony callus formation: New bone replaces the soft callus.

4. Bone remodeling: Bone is reshaped to its original form.

Application: Proper immobilization is crucial to ensure correct alignment and healing of the bone.

Additional info: These notes expand on the skeletal system study guide by providing definitions, examples, and academic context for each topic, making them suitable for exam preparation in Anatomy & Physiology.