The axial skeleton forms the body’s central axis and mainly provides support and protection. The appendicular skeleton consists of the limbs and the girdles attaching them to the axial skeleton, so it is primarily responsible for movement.
Bones and functions
The adult human skeleton normally has 206 bones: 80 in the axial skeleton and 126 in the appendicular skeleton.
| Division | Main bones | Principal functions |
|---|---|---|
| Axial skeleton | Skull, vertebral column, ribs and sternum | Supports posture; protects the brain, spinal cord, heart and lungs; provides attachment points for muscles |
| Appendicular skeleton | Pectoral girdle, upper limbs, pelvic girdle and lower limbs | Enables locomotion and manipulation; transfers forces between the limbs and axial skeleton |
The axial skeleton establishes the body’s central framework. For example, the vertebral column supports the head and trunk while protecting the spinal cord, and the thoracic cage protects organs in the chest.
The appendicular skeleton enables movement around joints. The pectoral girdle attaches the upper limbs to the trunk and allows a wide range of motion, while the pelvic girdle transfers body weight to the lower limbs and provides greater stability.
This distinction links to IB SEHS subtopic B.1.1 Anatomical position, planes and movement. Movements such as flexion, extension, abduction and adduction often involve appendicular bones moving relative to the axial skeleton within defined anatomical planes.
A common misconception is that every bone near the pelvis belongs to the appendicular skeleton. The hip bones form the appendicular pelvic girdle, but the sacrum and coccyx are part of the axial vertebral column.
Exam technique
If asked to “distinguish” the divisions, identify both their composition and function: central support and protection for the axial skeleton versus limb attachment and movement for the appendicular skeleton. Include named examples from each division rather than describing only their locations.
