Bones are classified into five categories based mainly on their shapes. These shapes are closely related to the roles bones perform, such as providing leverage, supporting the body, or protecting tissues. Understanding the categories makes it easier to connect a bone’s appearance with its location and function.
A baby typically has about 270–300 bones at birth. Some are made entirely of cartilage, a flexible tissue. As development proceeds, some bones fuse together, resulting in the 206 bones typically found in an adult skeleton.
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What are the five bone classifications?
Long, short, flat, irregular, and sesamoid bones. The categories are based primarily on bone shape.
What defines a long bone, and what does it do?
A long bone is cylindrical and longer than it is wide. It functions as a lever that moves when muscles contract; examples include the femur and humerus.
Where are short bones found, and what are their functions?
The human skeleton’s short bones are the carpals in the wrists and tarsals in the ankles. They provide stability and support while allowing limited motion.
How do flat and irregular bones differ?
Flat bones are typically thin and often curved; they provide muscle attachment and often protect organs. Irregular bones have complex shapes that do not fit the other categories, such as vertebrae and many facial bones.
What is the role of sesamoid bones, and which are found in everyone?
Sesamoid bones are small, round bones embedded in tendons that help protect tendons from compressive forces. The patellae are the sesamoid bones found in everyone.
Quiz questions
What is the primary basis for classifying bones into five categories?Answer: Their shape.
Which description best fits short bones?Answer: Their length, width, and thickness are approximately equal.
What is a major function of long bones?Answer: They act as levers when muscles contract.
What typically happens to the number of bones as a person develops from infancy to adulthood?Answer: Some bones fuse, leaving about 206 bones in adulthood.
How do the timing of bone length growth and bone density increase differ?Answer: Length growth usually ends around ages 16–18, while density rises into the late 20s.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.