Pearson Edexcel International GCSE Human Biology 4: Bones, muscles and joints

Movement depends on a living support system, not on bones or muscles acting alone. Pearson Edexcel International GCSE Human Biology (4HB1) Topic 4 covers the axial and appendicular skeletons, long-bone organization, elbow, shoulder and intervertebral joints, synovial-joint structure, antagonistic action of biceps and triceps, dietary support for bone and muscle, and osteoporosis. The topic links anatomy to force transmission, stability, repair and disease risk.

1. Functions of the skeleton

The skeleton supports soft tissues, protects organs, provides attachment and levers for muscles, stores minerals and contains marrow involved in blood-cell production. It is living tissue that remodels in response to load and physiological signals.

The axial skeleton forms the central axis: skull, vertebral column and ribcage. The skull protects the brain; vertebrae protect the spinal cord while allowing controlled movement; ribs and sternum protect thoracic organs and contribute to breathing mechanics.

The appendicular skeleton includes shoulder girdle, pelvic girdle and limbs. The scapula and clavicle position the upper limb and allow wide movement. The pelvis transfers body weight to lower limbs and protects pelvic organs. Limb bones act as levers around joints.

Axial does not mean “all bones near the middle”, and appendicular does not mean only hands and feet. Use the named components required by Pearson.

2. Long-bone structure

A long bone such as the femur has a shaft and expanded ends called epiphyses. Compact bone forms a strong dense outer region, especially around the shaft, resisting bending and compression. Spongy bone forms an internal lattice, prominent toward the epiphyses, providing strength with lower mass and containing marrow spaces.

Articular cartilage covers joint surfaces at epiphyses, reducing friction and absorbing shock. The central shaft contains a marrow cavity. Blood vessels and living cells support growth, repair and remodeling.

Bone architecture distributes material rather than making the whole bone solid. A completely solid bone would be heavy, while a thin hollow shell without internal organization would resist some loads poorly.

3. Joint types and examples

A joint is where two or more bones meet. Its structure balances movement and stability.

The elbow is mainly a hinge synovial joint, allowing flexion and extension in one principal plane. The shoulder is a ball-and-socket synovial joint, allowing movement in many directions and rotation. Its mobility comes with less inherent stability than the deeper hip joint.

Intervertebral joints include cartilaginous connections between vertebral bodies. Intervertebral discs allow limited movement, absorb shock and distribute compression. Small movements across many vertebrae combine to produce flexibility while protecting the spinal cord.