Bones and Joints
Bone
Bone is strong and highly resistant. It is rich in calcium and phosphorus, which are deposited in the bone matrix. The structure of bone includes two types of bone tissue: compact (dense) and spongy (porous).
Quick Fact
Spongy bone is lighter and found at the ends of long bones. Compact bone is dense and forms the hard outer layer, providing strength and protection.
Important Concept
Bones are composed of two main types of tissue: compact bone, which is dense and strong, and spongy bone, which is lighter and porous. Both types work together to provide strength, flexibility, and reduce overall weight.
Common Mistake
It’s incorrect to assume that all bone is solid. In reality, spongy bone contains many spaces and is crucial for reducing bone weight and housing bone marrow.
Questions
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Compact bone is dense and forms the strong outer layer of bone, while spongy bone is porous and lighter, found mostly at the ends of long bones.
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Bones are rich in calcium and phosphorus, which help give bones strength and rigidity, and are also essential for other body functions.
Think Like a Scientist
Investigation: How do heat and acid affect the properties of bone?
Materials: Three similar chicken bones, alcohol lamp, vinegar, beaker
Instructions:
Follow these steps to investigate how different treatments change bone strength:
Step 1: Soak one bone in vinegar and leave it for a few days.
Step 2: Hold another bone in a flame using tongs. Let it burn for a short time without charring completely.
Step 3: Leave the third bone untreated as a control sample.
Step 4: After all treatments, compare the bones in terms of flexibility, hardness, and breakability.
Show Answer
The untreated bone is the strongest because it still contains both collagen and minerals.
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The vinegar-soaked bone is the softest because the acid dissolves minerals like calcium, leaving only soft collagen.
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The burned bone is most brittle because the heat destroys collagen, leaving only the hard but fragile mineral portion.
Cartilage
Cartilage is found at the tip of the nose, the outer ear, and where bones meet at joints. It is soft and flexible, and it prevents bones from rubbing against each other at the joints.
Common Mistake
Some people think cartilage is the same as bone. In fact, cartilage is softer, more flexible, and lacks the mineral hardness of bone. It also takes much longer to heal when damaged.
Questions
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Cartilage cushions the ends of bones in joints, allowing smooth movement and preventing the bones from rubbing directly against each other.
Joints
The place where bones connect is called a joint.
There are different types of joints in the body. Some joints allow movement in multiple directions, like the joint between the arm and shoulder. Some joints allow movement in only one direction, such as the elbow joint.
Some joints have limited movement, like the joints between the vertebrae. Other joints do not move at all and are completely fixed, like the joints between the bones of the skull.
The tough connective tissue that holds bones together at the joint is called a ligament.
Joints help the skeleton remain connected while allowing various types of movement.
Quick Fact
Ligaments are strong connective tissues that stabilize joints by linking bones together.
Important Concept
Joints are categorized by their range of movement: freely movable (like the shoulder), partially movable (like the spine), and immovable (like the skull).
Common Mistake
It’s a common misconception that all joints allow movement. In reality, some joints — like those in the skull — are fixed and allow no movement at all.
Questions
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Ligaments are strong connective tissues that hold bones together at a joint, helping stabilize the joint while allowing movement.
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A movable joint is the shoulder joint, which allows movement in multiple directions. An immovable joint is the joint between skull bones, which does not allow movement.
Did You Know?
- In a dislocation, the bone moves out of its normal position at the joint.
- In a sprain, the joint has moved in an abnormal direction.
- In arthritis, the cartilage or bone at the joint is damaged or worn away.