Skeletal System Overview and Functions

Skeletal System Overview

• The skeletal system has two main parts: axial and appendicular.
• The axial skeleton forms the central core of the body, including the head, neck, and trunk.
• It contains approximately 80 bones.
• It does not include long or short bones.
• The appendicular skeleton consists of the upper (UE) and lower (LE) extremities.
• It includes bones of the arm, forearm, hand, pelvis, thigh, leg, and foot.
• The appendicular skeleton contains approximately 126 bones.
• It attaches to the axial skeleton.

Purposes of the Skeletal System

• Support for soft tissues.
• Framework for shape and support.
• Protection of vital organs.
• Levers for body movement.
• Production of red blood cells.
• Storage of calcium and minerals.

Classification of Bones

• Long bones: longer than they are wide (e.g., femur, humerus). They have large articular surfaces and articulate with more than one bone.
• Short bones: roughly equal in length and width (e.g., carpals, tarsals). They have large articular surfaces and articulate with more than one bone.
• Flat bones: broad and thin (e.g., ribs, scapula, cranial bones).
• Irregular bones: complex shapes (e.g., vertebrae, facial bones).

Bone Types: Compact and Spongy

• Compact bone: dense, strong, and found primarily in the shaft (diaphysis) of long bones and outer surfaces. Its structural units are called osteons.
• Spongy bone: irregular spaces giving a sponge-like appearance. Located primarily in the epiphysis of long bones and the center of other bones, it contains a latticework of bars and plates of bony tissue called trabeculae.

Parts of a Long Bone

• Epiphysis: the large end of the bone. Contains spongy bone and is covered by articular cartilage. In children, it includes an epiphyseal plate (growth plate).
• Diaphysis: the shaft of a long bone. It contains compact bone with a medullary cavity (hollow center) containing bone marrow.
• Periosteum: a fibrous membrane that covers the entire bone surface except at articular surfaces. Serves as tendons and ligament attachment sites.
• Medullary Cavity: a hollow center within the diaphysis that contains bone marrow.
• Endosteum: a thin membrane lining the medullary cavity.

Formation and Growth of Bone

• Bones initially develop as a cartilaginous model.
• Bone tissue progressively replaces cartilage, beginning in the diaphysis and then extending toward the epiphyses.
• The epiphyseal plate, located between the diaphysis and epiphyses, is responsible for bone growth in length.
• Once the epiphyseal plate is closed, further long bone growth stops.
• Bone remodeling and adaptation to stress occur throughout life, according to Wolff's Law.

Special Bone Types

• Sesamoid bones: small, located within soft tissue where tendons cross the ends of long bones. They protect tendons from wear. (Patella is a primary example.)
• Wormian bones: small bones sometimes found within suture lines in the skull.

Explore the essential components and functions of the skeletal system in this quiz. Understand the differences between the axial and appendicular skeleton and learn about the classification of bones. Test your knowledge on the roles of the skeletal system including support, protection, and mineral storage.