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Living bone and clever joints

Science · The Human Body · ages 19-20

Name ______________________ Date ____________

What does articular cartilage do at the contacting surfaces of a synovial joint?
- Produces the fluid by pumping blood into the joint
- Spreads load and helps reduce friction
- Attaches a contracting muscle directly to a bone
Which pairing describes the cell roles in bone remodelling?
- Osteoclasts remove matrix; osteoblasts deposit matrix
- Osteoblasts remove matrix; osteoclasts deposit matrix
- Osteoblasts deposit matrix; osteoclasts form cartilage
A connective-tissue cord attaches a muscle to a bone across the elbow. What is it?
- A ligament
- Articular cartilage
- A tendon
An astronaut loses some leg-bone mass after months with reduced weight-bearing in microgravity. Which change explains this loss?
- Osteoclast removal exceeds osteoblast formation
- Bone formation and removal stop at the same time
- Osteoblast formation exceeds osteoclast removal
The shoulder can bend in several directions and rotate. Which joint structure permits these movements?
- A hinge articulation
- A ball-and-socket
- A plane articulation
In a still-bone model, the muscle and load produce opposite moments. Their perpendicular moment arms are 4 cm and 20 cm. Ignore all other moments. How does muscle force compare with the nonzero load force?
- It is smaller, because its moment arm is shorter
- It is equal, because the bone is being held still
- It is larger, to balance the load's longer arm
A bone is held still. A 30 N load has a 15 cm moment arm; one muscle has a 3 cm arm. Their moments oppose; all other moments are neglected. Sam sets muscle force to 30 N, saying it must equal the load. Which calculation corrects this?
- 30 × 3 / 15 = 6 N
- 30 × 15 / 3 = 150 N
- 30 × 15 / 15 = 30 N
The hip's deep socket and strong supporting ligaments give it a wider range of movement than the shoulder.
Circle one: True False

Answer key

For grown-ups. Fold this page away before handing over the rest.

Living bone and clever joints W1-mt_1_q3aL7E5D-s1

Spreads load and helps reduce friction · Articular cartilage covers contacting bone surfaces. It distributes load and works with synovial fluid to allow low-friction movement.
Osteoclasts remove matrix; osteoblasts deposit matrix · Osteoclasts resorb existing bone matrix. Osteoblasts deposit new matrix, which later mineralises.
A tendon · A tendon attaches muscle to bone and carries the muscle's pull. A ligament connects bone to bone.
Osteoclast removal exceeds osteoblast formation · Reduced loading can contribute to net bone loss when osteoclasts remove more matrix than osteoblasts replace.
A ball-and-socket · The shoulder is a ball-and-socket joint. Its rounded head and socket permit bending in several directions and rotation.
It is larger, to balance the load's longer arm · Moment balance gives muscle force × 4 = load force × 20. The muscle force is five times the load force.
30 × 15 / 3 = 150 N · Balance moments: muscle force × 3 = 30 × 15. The muscle force is 150 N. The joint reaction also contributes to force balance, so muscle and load need not be equal.
False · Those structures support stability and weight bearing while limiting hip movement. The shoulder's shallower socket and looser capsule permit a wider range.