Question

When the knee moves back and forth as a person walks, what keeps the surfaces of the leg bones from rubbing against each other? A. The articular cartilage B. The epiphyses C. The periosteum D. A sheath of smooth muscle

Short answer

A. The articular cartilage

Step-by-step solution

Understand the Knee Joint

The knee joint is where the femur (thigh bone) and tibia (shin bone) meet. For smooth movement and to prevent damage, certain structures within the joint provide cushioning and reduce friction.

Identify the Correct Structure

Among the options provided, determine which structure is responsible for reducing friction and cushioning the bones.

Analyze the Options

Option A: The articular cartilage is a smooth, white tissue that covers the ends of bones where they come together to form joints. It enables bones to glide over each other with minimal friction. Option B: The epiphyses are the ends of long bones, but they do not specifically prevent rubbing in the joint.Option C: The periosteum is a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints.Option D: A sheath of smooth muscle is not found within the knee joint.

Choose the Correct Answer

Based on the analysis, the correct answer is Articular Cartilage, as it covers the ends of bones and ensures smooth movement without friction.

Key concepts

Articular Cartilage

Articular cartilage is the smooth, white tissue that covers the ends of bones where they meet to form joints. This tissue has several important roles in the knee joint.

• It allows bones to glide over each other smoothly, reducing friction.
• It acts as a cushion, absorbing shocks during movements.
• It provides a smooth, lubricated surface for articulation.

Without articular cartilage, the ends of bones would rub against each other, causing pain and damage. This cartilage is essential for healthy joint function.

Bone Friction Reduction

Reducing friction between bones is crucial for joint health and mobility. In the knee joint and other joints, several mechanisms work together to achieve this:

• Articular Cartilage: As mentioned, this cartilage covers the bone ends and is key to reducing friction.
• Synovial Fluid: This viscous fluid is secreted by the synovial membrane and lubricates the joint, further reducing friction.
• Menisci: These are C-shaped pieces of cartilage that act as a cushion and stabilize the knee joint.

All these components ensure that the bones move smoothly against each other, protecting them from wear and tear.

Joint Structures

The knee joint is a complex structure composed of several parts that work together for smooth movement and stability. Some important structures include:

• Femur: The thigh bone.
• Tibia: The shin bone.
• Patella: The kneecap.
• Ligaments: These strong bands of tissue connect bones and provide stability. Important ligaments in the knee include the ACL (anterior cruciate ligament) and the PCL (posterior cruciate ligament).
• Menisci: Cushioning cartilages that provide additional shock absorption.

All these components are vital for the knee's function, helping to bear weight, absorb shocks, and enable movement.