Chapter 7: The Skeletal System – Structure, Components, and Functions

Chapter 7: The Skeletal System

Learning Outcomes

This chapter introduces the major tissues and organs of the skeletal system, their organization, and their functional significance. Students will learn to identify and classify bone markings, describe their functions, and distinguish between adult and fetal skulls.

• Identify tissues and organs of the skeletal system and their anatomical relationships.

• Classify bone markings and describe their functions.

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

LO1: Skeletal System Components

Bones, Cartilages, and Ligaments

The skeletal system is composed of three primary types of connective tissues: bone, cartilage, and ligaments. Each plays a distinct role in structure and function.

• Cartilage: A flexible connective tissue that serves as a precursor to bone tissue during development and covers most joints in adults, providing smooth surfaces for movement.

• Ligaments: Strong bands of fibrous connective tissue that connect bones to each other at joints (articulations), stabilizing and supporting the skeleton.

• Bone: A mineralized connective tissue containing blood, bone marrow, cartilage, adipose, nervous, and fibrous connective tissues. Bones provide structural support, protect organs, and serve as sites for muscle attachment.

Types of Cartilage in the Skeletal System

• Hyaline Cartilage: Found at articular surfaces of bones, costal cartilages (ribs), respiratory structures, and nasal cartilages. It is the most common type and forms the initial model for endochondral ossification (bone development).

• Elastic Cartilage: Located in the external ear and epiglottis. It contains elastic fibers, providing high elasticity and flexibility.

• Fibrocartilage: Found in intervertebral discs and knee menisci. It is highly compressible and has great tensile strength, making it ideal for resisting pressure and tension.

LO1: Bones in the Typical Adult Skeleton

Overview of Bone Count and Organization

The adult human skeleton typically consists of 206 bones, organized into two main divisions: the axial and appendicular skeletons.

• 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, including:

  • Pectoral girdles (4 bones)

  • Upper limbs (60 bones)

  • Hip bones (2 bones)

  • Lower limbs (60 bones)

Key Definitions and Examples

• Articulation: A joint where two bones meet, allowing for movement and flexibility.

• Endochondral Ossification: The process by which bone tissue replaces hyaline cartilage models during fetal development and growth.

• Example: The femur (thigh bone) is part of the appendicular skeleton and articulates with the pelvis at the hip joint.

Additional info:

• Some bones, such as sesamoid bones (e.g., the patella), form within tendons in response to mechanical stress.

• At birth, humans have approximately 270 bones, but some fuse during development to reach the adult count of 206.