The 206 bones that hold us up, the joints that let us move and the muscles that pull in pairs.
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The skeleton supports the body, protects delicate organs (the skull protects the brain, the rib cage the heart and lungs), allows movement, makes blood cells in bone marrow and stores calcium. An adult has 206 bones. The axial skeleton (80 bones) is the skull, hyoid, ear ossicles, vertebral column, sternum and ribs. The appendicular skeleton (126 bones) is the limbs and the girdles that attach them. Bone is hard and rigid; cartilage is softer and flexible, found in the nose tip, ear flap and ends of bones.
The vertebral column has 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 coccygeal vertebrae. How many in all?
7 + 12 + 5 + 5 + 4 = 33. The sacral and coccygeal ones fuse in an adult, leaving 26 separate bones.
Check the total: axial 80 + appendicular 126.
80 + 126 = 206 bones.
Why is the skull made of fused bones?
Fused bones form a rigid box that protects the brain.
A joint is where two bones meet. Fixed (immovable) joints, such as those between skull bones, allow no movement. Slightly movable joints, as between vertebrae, allow little movement. Freely movable (synovial) joints are of several kinds: ball-and-socket (shoulder, hip) move in all directions; hinge (elbow, knee, fingers) move in one plane like a door; pivot (neck, between atlas and axis) allow rotation; gliding (wrist, ankle) allow sliding. Ligaments hold the bones together; synovial fluid lubricates the joint.
Name the joint at the (a) shoulder, (b) elbow, (c) neck that lets you say "no".
(a) Ball-and-socket. (b) Hinge. (c) Pivot joint.
What is the difference between a ligament and a tendon?
A ligament joins bone to bone. A tendon joins muscle to bone.
What is the function of synovial fluid?
It lubricates the joint, reducing friction between bone ends.
A muscle can only contract (shorten) and relax; it can pull but cannot push. So muscles work in antagonistic pairs. At the elbow the biceps (front of the upper arm) contracts to bend the arm while the triceps (back) relaxes; the triceps contracts to straighten it while the biceps relaxes. Muscles are attached to bones by tendons. Locomotion is movement from one place to another, such as walking, swimming or flying.
Which muscle contracts when you bend your arm? Which one relaxes?
The biceps contracts; the triceps relaxes.
Why do muscles work in pairs?
A muscle can only pull. One muscle of a pair pulls a bone one way, the other pulls it back.
Name two forms of locomotion in animals.
Any two: walking, running, flying, swimming, crawling, hopping.
1. Name three functions of the skeleton.
2. How many bones are there in an adult human skeleton?
3. Name the two divisions of the skeleton.
4. Which part of the skeleton protects the heart and lungs?
5. Differentiate bone from cartilage.
6. Name one example each of a hinge joint and a ball-and-socket joint.
7. What are antagonistic muscles?
8. What joins muscle to bone?
9. How many bones make the skull?
10. Why can we not push a bone with a muscle?