Questions: Skeletal System: Bones and Joints

Question 1

Babies are born with about 270 bones, but adults have only 206. What happened to the extra bones?

• A. Some bones dissolve as you age
• B. Some bones are removed during growth
• C. Some bones fuse together during development
• D. The body reabsorbs unnecessary bones

Answer: (C)

Many of a baby's bones are initially separate pieces of bone and cartilage that gradually fuse together as the child grows. For example, the skull starts as several separate plates (which allow the head to compress during birth and the brain to grow rapidly) that fuse into a solid skull during childhood. The sacrum at the base of the spine starts as five separate vertebrae that fuse into one bone by adulthood.

Question 2

Bones are dry, solid, lifeless structures that don't change once you stop growing.

• T. True
• F. False

Answer: False

Bones are living tissue with blood vessels, nerves, and active cells. Throughout your entire life, specialized cells called osteoclasts break down old bone while osteoblasts build new bone -- a process called remodeling. Your entire skeleton is replaced roughly every 7-10 years. Bones also respond to stress: weight-bearing exercise makes bones denser and stronger, while prolonged inactivity causes them to weaken.

Question 3

Why does your elbow only bend in one direction while your shoulder can rotate in a circle? What's different about these two joints?

Model answer: The elbow is a hinge joint, shaped like a door hinge so it can only move back and forth in one plane. The shoulder is a ball-and-socket joint, where a round bone end sits in a cup-shaped socket, allowing rotation in many directions. The shape of the joint determines the type and range of movement it allows.

Joint function follows directly from joint structure. A hinge joint's interlocking bones physically prevent side-to-side motion, providing stability for tasks like lifting. A ball-and-socket joint sacrifices some stability for range of motion, which is why shoulders are more flexible but also more prone to dislocation than elbows.