The Skeletal System

This lesson introduces the anatomy and functions of the skeletal system. This lesson also explores how bone forms, remodels, and constantly changes as a person grows.

Skeletal System Overview

A human is born with roughly 270 bones. As a person grows, this number decreases to approximately 206. This is because many of the bones fuse.

For Example

Half of the pelvic bone has three separate bones at birth: the ilium, ischium, and pubis. By adulthood, these bones fuse into one bone called the hipbone.

Anatomically, the skeletal system is divided into two major divisions: axial skeleton and appendicular skeleton. The axial skeleton consists of the bones of the skull, sternum, vertebral column, and ribcage. The appendicular skeleton comprises the bones of the upper and lower extremities and the associated girdles that connect the extremities to the vertebral column. The following table summarizes the number of bones found in each skeletal division.

Twenty-four of the bones in the vertebral column are called the pre-sacral vertebrae. These consist of 7 cervical, 12 thoracic, and 5 lumbar vertebrae. The last two bones of the vertebral column are the sacrum and coccyx.

Axial80 bones
Inner ear ossicles6
Skull and Hyoid23
Sternum and Ribs25
Vertebral Column26
Appendicular126 bones
Pectoral Girdle4
Upper Extremities60
Pelvic Girdle2
Lower Extremities60

The skeletal system consists of bonescartilage, and ligaments that are tightly bound together to form a strong, yet flexible, framework. Bone is an active form of connective tissue. This tissue plays a role in many of the functions of the skeletal system:

  • Support: Bones and cartilage support body posture because both structures are rigid. They also allow a person to remain upright and provide a framework to which soft tissues like muscles and organs can attach.
  • Movement: Bones of the skeletal system interact with the muscular system to help the body move. Bones themselves cannot move. But when connected to each other by ligaments, along with the action of muscles, a human body can move.
  • Protection: The skeletal system protects vital organs from external damage. The skull protects the brain, the vertebral column protects the spinal cord, and the sternum and ribcage protect the lungs.
  • Mineral storage: Bone functions as a storage site for important minerals like calcium and phosphorus. These minerals are used for a variety of physiological functions in the body.
  • Hematopoiesis: This is the process bones use to produce red blood cells and stem cells, which differentiate to a variety of different cell types in the body.

The following image illustrates the anatomy of the skeletal system.

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