The Human Brain

Some Basic Facts

The cortex (sometimes called ‘grey matter’) represents the outer layer of the brain and is only about 2 – 5mm thick. It is home to our mental activity, thanks to the 100 billion or so neurons (excitable cells) that form trillions of axons—or bridges linking one neuron to another. When stimulated, the neuron sends electrical impulses down the axon to the synapse. The synapse is a gap between axons. Ions (charged atoms or molecules) composed of sodium and potassium are fired across the synapse and down the axon to the next neuron. In this way, neurons (which on their own are not very ‘smart’) can “communicate” with tens of thousands of other neurons in a fraction of a second.