Chapter 7: The Skeletal System

Learning Outcomes

• Describe the tissues and organs that make up the skeletal system and their anatomical relationships.

• Identify and classify bone markings and explain their functions.

• Name and describe the adult skull bones, their articulations, and differences between adult and fetal skulls.

Skeletal System Components

Main Tissues and Organs

The skeletal system is a complex organ system that provides structural support, protection, and facilitates movement. It is composed of several types of tissues and organs:

• Bone: A mineralized connective tissue that forms the rigid framework of the body. It contains blood, bone marrow, cartilage, adipose, nervous, and fibrous connective tissues.

• Cartilage: A flexible connective tissue that serves as a precursor to bone in development and covers most joints in adults, reducing friction and absorbing shock.

• Ligaments: Dense bands of connective tissue that connect bones at joints (articulations), providing stability.

Location and Relationships: Bones are interconnected by ligaments at joints, while cartilage is found at joint surfaces, in the nose, ears, and other specific locations.

Skeletal Cartilages

Types and Functions

Cartilage is classified based on its structure and function:

• Hyaline Cartilage: Found in articular surfaces, costal (rib) cartilage, respiratory tract, and nasal cartilage. It serves as a model for endochondral ossification during bone development.

• Elastic Cartilage: Located in the ears and epiglottis, providing high elasticity and flexibility.

• Fibrocartilage: Present in intervertebral discs and knee menisci, characterized by high compressibility and tensile strength.

Example: The meniscus in the knee is fibrocartilage, allowing it to withstand compressive forces during movement.

Bones in the Adult Skeleton

Classification and Numbers

The adult human skeleton typically consists of 206 bones, divided into two main groups:

• Axial Skeleton: Forms the central axis of the body and includes:

  • Skull (22 bones)

  • Auditory ossicles (6 bones)

  • Hyoid bone (1 bone)

  • Vertebral column (33 bones)

  • Thoracic cage (25 bones)

• Appendicular Skeleton: Comprises the limbs and girdles:

  • Pectoral girdles (4 bones)

  • Upper limbs (60 bones)

  • Hip bones (2 bones)

  • Lower limbs (60 bones)

Additional info: Newborns have approximately 270 bones, which fuse during development to form the adult count.

Summary Table: Skeletal System Components

Key Terms and Definitions

• Articulation: A joint where two bones meet.

• Endochondral Ossification: The process by which bone tissue forms from cartilage models.

• Meniscus: Crescent-shaped fibrocartilage structure in the knee.

Applications and Examples

• Clinical Relevance: Damage to cartilage (e.g., meniscus tear) can impair joint function and require surgical intervention.

• Developmental Biology: Understanding bone fusion in infants is important for pediatric care.