Ronald B. Coleman, Jr.
The human skeleton is the support system of the human body. Without the skeletal system human beings would not stand erect. Although we cannot see the skeletal system, it has a huge effect on physical activity. The human skeleton is located underneath the layers of skin, fatty tissue, and muscular fibers. Most sources conclude that the average adult has 206 bones that make up the entire skeleton. Bones take on a variety of shapes, sizes, and functions. At birth, infants can have almost 300 bones in their bodies. These bones fuse together over time and create the adult skeleton.
In total, the human skull is made of 29 bones that are fused together to protect the brain. The face makes up 14 of these bones. Each human hand has 27 bones and the wrist consists of 8 bones. Each foot and ankle combines to add another 26 bones. The breastbone and ribs serve a similar protective function: they keep the heart and lungs safe from pressure and impact. Bones in the arms, shoulders, torso, and legs are important because they serve a function of movement. Stronger bones can move more quickly and more powerfully against tension.
Most bones have three layers: periosteum, hard bone, and a spongy core. Periosteum is the outer layer of bone. The second layer of bone is the strongest and hardest part of the skeleton. This hard bone encloses the softer, lighter spongy center. Since the periosteum is made of cells that repair broken bone, bones heal themselves on the outside first. Almost all bones are made from a cartilage precursor. The cartilage forms collagen fibers that create a tough, yet flexible bone material
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. However, the clavicle and top of the skull are made from connective tissue that is not comprised of cartilage.
The breastbone, hip, and vertebrae of skeletal system are made primarily of spongy bone. Spongy bone in young people is strong but light in weight. As a person ages, some of the spongy bone in the body loses calcium and may become thin, and fragile. The elderly and adults who do not take in enough calcium are susceptible to breaking their hip because of the natural process of calcium depletion.
The major bones in the hip and leg are connected at joints. Joints represent pockets where cartilage, soft tissue, protects two bones from rubbing against one another. The head of the femur fits comfortably into the side of the pubis. The patella (knee cap) is attached to both the femur and upper tibia (lower leg bone) by the patella tendon. In the lower leg, the tibia is the weight-bearing bone. The fibula serves primarily as an attachment for muscles. As a result, the fibula does not grow to be as big or as strong as the tibia. Children who engage in sports and high impact activities are likely to develop bigger and stronger bones because high-tension (think running and jumping) can increase bone growth.
Students may enter this unit with an understanding that joints are formed where two or more bones meet. Joints allow bones to move; however, ligaments are the strong fibers that keep everything together while giving us the flexibility and dexterity to move. Joints, however, take on many different formations. Ball and socket joints allow bones to move in many different directions. Hinge joints allow either vertical or horizontal movement (but not both), and pivot joints allow for one bone to swivel around the other
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.
What facts should students know about the skeletal system?
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§ How many bones are in the adult skeleton? (206)
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§ How many bones are in each hand? (27)
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§ How many bones are in each foot? (26)
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§ How many bones are in the hands and feet combined? (106)
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§ How many bones are in the adult skull? (28)
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§ How many bones are in the face? (14)
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§ How many bones are in each ear? (3)
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§ How many vertebrae are in the adult skeleton? (26)
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§ How many bones are in the shoulder? (2)
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§ What is the most frequently fractured bone in the body? (Clavicle)
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§ How many bones are in the upper leg? (1)
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§ How many bones are in the lower leg? (2)
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§ What is the longest bone in the body? (Femur: thigh bone)
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§ The femur makes up approximately what percent of body height? (1/4 or 25%)
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§ What is the smallest bone in the body? (Stirrup: ear bone)
