Skeletal System Overview 7.1

Overview

This section explains the main divisions of the human skeletal system, their functions, and the components of the axial and appendicular skeletons.

Functions of the Skeletal System

• The skeletal system supports and shapes the body and its structures.
• Adults have 206 bones; bone numbers decrease with age as some fuse together.
• The skeleton provides internal support to resist gravity and enables body movement via muscle attachment.
• The lower skeleton is specialized for stability during walking or running.
• The upper skeleton provides greater mobility for lifting, carrying, and rotating the head and trunk.
• The skeleton protects internal organs, including the brain, spinal cord, heart, and lungs.
• Bones store minerals like calcium and phosphate and house fat and blood-cell producing tissue (bone marrow).

Divisions of the Skeleton

• The skeleton is divided into the axial skeleton and appendicular skeleton.

The Axial Skeleton

• The axial skeleton forms the vertical, central axis of the body.
• It includes bones of the head, neck, chest, and back.
• The axial skeleton protects the brain, spinal cord, heart, and lungs.
• It serves as attachment for muscles that move the head, neck, back, and limbs.
• The adult axial skeleton consists of 80 bones: the skull (22 bones), hyoid bone, ear ossicles (6 bones), vertebral column (24 vertebrae, sacrum, coccyx), and thoracic cage (12 rib pairs and sternum).

The Appendicular Skeleton

• The appendicular skeleton includes all bones of the upper and lower limbs.
• It also includes the bones that attach each limb to the axial skeleton.
• There are 126 bones in the adult appendicular skeleton.

Key Terms & Definitions

• Axial skeleton — bones forming the central axis (skull, vertebral column, thoracic cage).
• Appendicular skeleton — bones of the limbs and girdles attaching them to the axial skeleton.
• Skull — bony structure protecting the brain, part of the axial skeleton.
• Vertebral column — series of vertebrae extending from the skull to the pelvis.
• Thoracic cage — rib cage and sternum protecting the heart and lungs.
• Hyoid bone — U-shaped bone in the neck, supports the tongue.
• Ear ossicles — three small bones in each middle ear involved in hearing.

Action Items / Next Steps

• Review the components of the axial and appendicular skeleton for identification.
• Read the next section on the skull for detailed bone structure.