Unit 10 Joints and movement
Key unit competence: Relate the main types of joints to their functions and explain how muscles move bones.
Key ideas
- A joint is a place where two or more bones meet. Joints allow movement, give flexibility and, in some cases, protect organs.
- Types of joints: immovable (fixed, fibrous) joints, e.g. sutures between skull bones; slightly movable (cartilaginous) joints, e.g. between vertebrae (separated by cartilage discs) and at the pubic symphysis; freely movable (synovial) joints, e.g. hip, knee, elbow, shoulder.
- Ball and socket joints (shoulder, hip): the round head of one bone fits in a cup-shaped socket; movement in all directions (rotation). Hinge joints (elbow, knee, finger joints): movement in one plane only, like a door. Pivot joints: rotation, e.g. between the atlas and axis vertebrae (turning the head) and in the forearm. Gliding joints: bones slide over each other, e.g. wrist and ankle bones.
- Structure of a synovial joint: articular (hyaline) cartilage covers the bone ends (smooth, reduces friction, absorbs shock); a synovial membrane secretes synovial fluid (lubricates, nourishes cartilage); a capsule encloses the joint; ligaments join bone to bone and hold the joint together (strong, slightly elastic).
- Tendons join muscle to bone; they are strong and non-elastic, so all the pull of the muscle moves the bone.
- Muscles can only pull (contract) and cannot push. They work in antagonistic pairs: when one contracts, the other relaxes.
- At the elbow (hinge): to bend (flex) the arm, the biceps contracts and the triceps relaxes; to straighten (extend) it, the triceps contracts and the biceps relaxes. The biceps is the flexor, the triceps the extensor.
- Healthy bones and joints: balanced diet with calcium, phosphorus and vitamin D (milk, small fish, beans, sunlight), regular exercise, good posture, warming up before sport, safe lifting (bend the knees), healthy body weight, avoiding smoking and alcohol abuse.
- Problems: arthritis (inflamed, painful joints), dislocation (bone forced out of its joint), sprain (stretched or torn ligament), fracture (broken bone), rickets and osteoporosis (weak bones).
Common misconceptions
- "Muscles push bones to straighten the arm." No: muscles only pull; the triceps pulls the forearm straight.
- "Ligaments join muscles to bones." No: tendons join muscle to bone; ligaments join bone to bone.
- "The skull has no joints." No: the skull bones are joined by immovable sutures.
- "Synovial fluid is blood in the joint." No: it is a lubricating fluid secreted by the synovial membrane.
Worked examples
Example 1. Explain how the arm is bent at the elbow.
Solution
The biceps muscle (attached by a tendon to the radius) contracts and shortens, pulling the forearm up. At the same time the triceps relaxes and is stretched. The elbow, a hinge joint, allows movement in one plane.
Example 2. Explain why a sprained ankle heals more slowly than a cut on the skin.
Solution
A sprain damages ligaments, which have a poor blood supply, so oxygen and nutrients for repair arrive slowly. The joint is also used whenever we stand, which strains the ligament again. Rest, ice, support and raising the foot help.
Practice questions
Define a joint and name three types of joints according to how much they move.
Show answer
A joint is where two or more bones meet. Immovable (sutures of the skull), slightly movable (between vertebrae), freely movable/synovial (hip, knee, elbow).
Common mistake: Naming muscles as joints.
Give one example and the type of movement of: (a) ball and socket; (b) hinge; (c) pivot joint.
Show answer
(a) Shoulder/hip: movement in all directions. (b) Elbow/knee: movement in one plane. (c) Atlas-axis (neck): rotation of the head.
Common mistake: Calling the knee a ball and socket joint.
State the function of each part of a synovial joint: cartilage, synovial fluid, ligament.
Show answer
Cartilage: smooth surface that reduces friction and absorbs shock. Synovial fluid: lubricates the joint and nourishes cartilage. Ligament: joins bone to bone and holds the joint in place.
Common mistake: Saying ligaments attach muscles.
Distinguish between a tendon and a ligament.
Show answer
A tendon joins muscle to bone and is non-elastic; a ligament joins bone to bone and is slightly elastic.
Common mistake: Mixing them up.
Explain how the triceps and biceps work together.
Show answer
They are antagonistic: to bend the arm, the biceps contracts and the triceps relaxes; to straighten it, the triceps contracts and the biceps relaxes.
Common mistake: Saying both contract together.
State four practices that promote healthy bones and joints.
Show answer
Eat food rich in calcium, phosphorus and vitamin D; exercise regularly; keep good posture; warm up before sport; lift loads correctly; keep a healthy weight; avoid smoking and alcohol abuse.
Common mistake: Giving only diet.
Distinguish between a sprain, a dislocation and a fracture.
Show answer
Sprain: ligament stretched or torn. Dislocation: bone displaced from its joint. Fracture: a broken bone.
Common mistake: Calling every injury a fracture.
Give first aid for a sprained ankle.
Show answer
Rest the ankle, apply ice or cold cloth, compress with a bandage, elevate the foot (RICE); see a health worker if pain is severe.
Common mistake: Massaging the ankle hard immediately.
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The elbow allows movement in: a. tendons 2. When a bone is forced out of its joint, it is a: b. one plane only, like a door 3. Muscles are attached to bones by: c. biceps contracts 4. To bend the arm at the elbow, the: d. dislocation Show answer
1 → b (one plane only, like a door) · 2 → d (dislocation) · 3 → a (tendons) · 4 → c (biceps contracts)
- It is a hinge joint.
- The shoulder is often dislocated.
- Tendons are strong and non-elastic.
- The biceps is the flexor.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
arthritis · malaria · pivot joint · a sprain of the knee ligaments- Turning the head from side to side uses a .
- A footballer's knee is painful and swollen after a twist, but no bone is broken. The likely injury is .
- A painful, inflamed joint is a sign of .
Show answer
1: pivot joint · 2: a sprain of the knee ligaments · 3: arthritis
- The atlas rotates on the axis.
- Twisting stretches ligaments.
- It is common in old age.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. The joints between skull bones are: a. Calcium 2. The knee joint is a: b. hinge joint 3. Synovial fluid in a joint: c. lubricates and reduces friction 4. Which nutrient, with vitamin D, keeps bones strong? d. immovable sutures Show answer
1 → d (immovable sutures) · 2 → b (hinge joint) · 3 → c (lubricates and reduces friction) · 4 → a (Calcium)
- They protect the brain.
- It moves in one plane.
- It is secreted by the synovial membrane.
- Milk and small fish are rich in calcium.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
antagonistic muscles · cartilage · dislocation · sprain- The smooth tissue covering bone ends in a joint is .
- Muscles that work in pairs, one contracting while the other relaxes, are .
- A stretched or torn ligament is a .
Show answer
1: cartilage · 2: antagonistic muscles · 3: sprain
- It reduces friction and absorbs shock.
- Biceps and triceps are an example.
- It is common in ankles.