Tissues in Action · Lesson 8 of 11
The Musculoskeletal System
“Every movement is a group project involving muscles, bones, joints and one very busy nervous system.”
• Identify the components of the musculoskeletal system. • Explain how muscles, tendons, bones and joints produce movement. • Describe the controlling role of nervous tissue. • Observe and compare movements at different body parts. • Estimate bone and muscle mass from body weight data.
Introduction
Hold one forearm still and slowly bend the elbow. A muscle changes shape, a tendon carries its pull, a bone rotates around a joint and nervous tissue controls the timing. Movement is therefore not the work of one tissue. It is an action produced by an entire coordinated system.
The musculoskeletal system contains bones, muscles, joints, cartilage, tendons and ligaments. Together they help the body stand upright, move, maintain posture and protect delicate organs. The nervous system controls and coordinates these actions.
Muscles can contract and produce a pulling force, but they cannot push a bone to a new position by themselves. A tendon attaches muscle to bone and transfers the pull. The joint provides the place where one bone can move relative to another. Cartilage cushions the bone ends, and ligaments stabilise the connection. Nervous tissue determines when and how strongly the muscles contract.
Problem
Trace the roles of tissues when the forearm bends.
- 1.Nervous tissue sends an instruction to an appropriate skeletal muscle.
- 2.The muscle contracts and becomes shorter.
- 3.Its tendon transmits the pulling force to a forearm bone.
- 4.The elbow joint allows the forearm to rotate in a permitted direction.
- 5.Ligaments stabilise the joint and cartilage cushions the contacting surfaces.
Activity: Let us investigate
The contribution of bones and muscles to total body weight can be estimated using percentages. The values vary with age, body composition and other individual differences, so the result is an estimate rather than a direct measurement. The source chapter uses about 12-15 per cent as an average adult bone contribution and broad adult muscle ranges of about 40-50 per cent for males and 30-40 per cent for females.
Problem
If an adult has a body weight of 60 kg and uses 13% for bone and 40% for muscle, what are the estimates?
- 1.Estimated bone mass = 60 × 13/100.
- 2.Estimated bone mass = 7.8 kg.
- 3.Estimated muscle mass = 60 × 40/100.
- 4.Estimated muscle mass = 24 kg.
- 5.These are approximate values based on chosen average percentages, not direct measurements of the individual.
The Musculoskeletal System in Action
Activity: Let Us Observe
Move the elbow, shoulder, knee, neck, fingers, toes and wrist. Some parts bend mainly in one direction, some rotate partly, and some move in several directions. The difference arises from the shape and arrangement of the joints at those locations.
A joint is a junction between two or more bones.
A joint allows or limits a particular movement, but it cannot move a bone on its own. Movement still requires muscular force. This distinction explains why a joint can be correctly shaped and healthy yet remain motionless unless muscles pull the connected bones.
| Body part | Typical observation | What the observation suggests |
|---|---|---|
| Elbow | Bends and straightens mainly in one direction | The joint strongly limits the path. |
| Shoulder | Moves forwards, backwards, sideways and in a circle | The joint permits movement in many directions. |
| Knee | Bends and straightens mainly in one direction | Movement is guided in one main plane. |
| Neck | Turns the head side to side | A rotating connection is present. |
| Wrist and fingers | Perform several smaller movements | Several bones and joints cooperate. |
Quiz
Which description best matches Joint?
Which term matches this description: A joint is a junction between two or more bones.
Which statement is a key takeaway from this lesson?
Which additional statement is also a key takeaway from this lesson?
Which further statement is also a key takeaway from this lesson?
Practice Problems
- List all six major components of the musculoskeletal system.
- Why can a joint not move a bone without muscular action?
- Explain the separate roles of tendon, ligament and cartilage during movement.
- Estimate bone mass for a 50 kg adult using 12% and 15% as the lower and upper values.
- Why should estimated tissue percentages not be treated as direct measurements?
- Compare the movement observed at the shoulder and elbow.
Key Takeaways
• The musculoskeletal system combines bones, muscles, joints, cartilage, tendons and ligaments. • Muscles supply force, tendons transmit it and joints permit controlled movement. • Nervous tissue coordinates the action. • Different joint structures allow different ranges of movement.