Overview of the Human Skeletal System: Structure, Divisions, and Bone Anatomy

Skeletal System Anatomy

Introduction to the Skeletal System

The skeletal system is a framework of bones connected at joints or articulations, providing support, protection, and movement for the human body. In adults, the skeleton consists of 206 bones, organized into two major divisions: the axial skeleton and the appendicular skeleton.

• Axial skeleton: Includes the skull, vertebral column, and bony thorax (thoracic cage).

• Appendicular skeleton: Comprises the bones of the limbs and girdles (shoulder and pelvic).

Joints (articulations) are the sites where two or more bones meet, allowing for movement and flexibility.

Main Divisions of the Skeleton

• Skull: Protects the brain and forms the structure of the face.

• Bony thorax (Thoracic cage): Includes the ribs and sternum, protecting vital organs such as the heart and lungs.

• Vertebral column: Supports the body and protects the spinal cord.

• Appendicular skeleton: Includes the pectoral girdle (shoulder), pelvic girdle (hip), and the bones of the upper and lower limbs.

Example: The femur is the longest bone in the body and is part of the appendicular skeleton.

The Adult Skeleton and Cartilage

Types of Cartilage and Their Locations

Cartilage is a flexible connective tissue found in various locations throughout the body, providing support and cushioning at joints and other structures.

• Hyaline cartilage: Found in the nose, trachea, larynx, costal cartilage, and articular surfaces of joints.

• Elastic cartilage: Present in the external ear and epiglottis.

• Fibrocartilage: Located in intervertebral discs, pubic symphysis, and menisci of the knee.

Example: The meniscus in the knee is a pad of fibrocartilage that helps absorb shock during movement.

Functions of Cartilage in the Skeleton

• Provides smooth surfaces for joint movement.

• Acts as a cushion between bones.

• Supports soft tissues (e.g., ear, nose).

Structure of a Long Bone

Gross Anatomy of a Long Bone

Long bones, such as the femur and humerus, have a complex structure designed for strength and mobility. The main regions and components include:

• Diaphysis: The shaft of the bone, composed mainly of compact bone.

• Epiphyses: The ends of the bone, containing spongy bone and articular cartilage.

• Medullary cavity: The central cavity within the diaphysis, lined by endosteum and containing yellow bone marrow.

• Periosteum: A dense connective tissue membrane covering the outer surface of the bone, containing blood vessels and nerves.

• Articular cartilage: Hyaline cartilage covering the joint surfaces of the epiphyses.

Microscopic Structure and Bone Markings

• Compact bone: Dense and strong, forming the outer layer of bones.

• Spongy bone: Porous and lightweight, found in the epiphyses and inside flat bones.

• Bone markings: Features on bones that serve as attachment points for muscles and ligaments, or as passages for nerves and blood vessels.

Common Bone Markings

Type	Description	Example
Process	Any bony prominence	Spinous process of vertebra
Condyle	Rounded articular projection	Femoral condyle
Foramen	Round or oval opening through a bone	Foramen magnum of the skull
Fossa	Shallow depression	Olecranon fossa of the humerus
Crest	Narrow ridge of bone	Iliac crest of the pelvis
Tuberosity	Large rounded projection	Tibial tuberosity

Bone Tissue and Blood Supply

• Perforating (Sharpey's) fibers: Collagen fibers that anchor the periosteum to the underlying bone.

• Nutrient arteries: Blood vessels that supply the bone tissue with nutrients and oxygen.

• Yellow bone marrow: Fat storage tissue found in the medullary cavity of long bones.

Example: The periosteum is essential for bone growth, repair, and nutrition.

Summary Table: Divisions and Components of the Adult Skeleton

Division	Main Components	Function
Axial Skeleton	Skull, vertebral column, thoracic cage	Protection of vital organs, support
Appendicular Skeleton	Limb bones, pectoral and pelvic girdles	Movement, manipulation of environment

Additional info: The images and notes provided are consistent with introductory college-level Anatomy & Physiology content, focusing on the structure and function of the skeletal system, types of cartilage, and bone anatomy.