Support, movement and the skeleton
What this domain tests
Functions of the skeleton, names and numbers of bones and vertebrae, long bone structure, synovial joints and antagonistic muscle action. Label-the-joint and explain-the-movement questions are standard, and marks are usually lost on tendon and ligament confusion.
Core rules
- Skeleton functions: support, protection of organs, movement through muscle attachment, storage of calcium and phosphate, and blood cell production in red marrow.
- Axial skeleton: skull, vertebral column, ribs and sternum. Appendicular skeleton: limbs and girdles.
- Vertebral column: 7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral and 4 fused coccygeal, giving 33 in the child and 26 in the adult. The atlas and axis are the first two cervical vertebrae and allow the head to nod and rotate.
- Long bone structure: periosteum, compact bone, spongy bone and marrow cavity, with cartilage at the ends to reduce friction.
- Joint types: hinge (elbow, knee) allows movement in one plane; ball-and-socket (shoulder, hip) allows movement in all planes including rotation; pivot (atlas and axis); gliding (carpal bones).
- Ligaments join bone to bone and hold the joint; tendons join muscle to bone. Cartilage and synovial fluid cushion and lubricate.
- Muscles can only pull, never push, so they work in antagonistic pairs: biceps as flexor and triceps as extensor at the elbow.
Worked example
Explain what happens when the forearm is raised towards the shoulder. The biceps contracts and shortens, pulling on its tendon attached to the radius, while the triceps relaxes and lengthens. The elbow is a hinge joint, so movement occurs in one plane only. The triceps cannot push the arm back down; when the arm is lowered the roles reverse. This is antagonistic action, and it explains why both muscles are needed for one movement.
Traps that cost marks
Reversing tendons and ligaments. Saying a muscle can push a bone. Writing that the shoulder is a hinge joint. Forgetting that the vertebral count differs between child and adult because of fusion.