Structure of the cerebral hemispheres
The cerebral hemispheres are the right and left hemispheres, joined by the corpus callosum made of nerve fibres. On the surface is grey matter – the cortex about 2–3 mm thick – and beneath it white matter. The cortex is folded into ridges and grooves, so many cells fit in the skull: it holds tens of billions of neurons. The hemispheres are divided into frontal, parietal, temporal and occipital lobes. Vision centres are in the occipital lobe and hearing in the temporal lobe; in front of the central groove is the motor zone, behind it the skin and muscle sensory zone; smell and taste centres have their own places. Sensory zones receive impulses from sense organs, motor zones set muscles into voluntary movement. Association zones link sensory and motor zones and analyse information; thinking, speech, memory and learning depend on them. The cortex is the basis of higher nervous activity.
Hemisphere map: colour the frontal, parietal, temporal and occipital lobes and mark the centres for vision, hearing, movement and skin sense. Logic question: why is the cortex folded?