Neurons are not like other cells, which are typically compact and spherical. Neurons are long and stringy, the better to pass on electrical signals from one to another. The main strand of a neuron is called an axon. At its terminal end, it splits into branch-like extensions called dendrites, as many as 400,000 of them. The tiny space between nerve cell endings is called a synapse. Each neuron connects with thousands of other neurons, giving trillions and trillions of connections—as many connections “in a single cubic centimeter of brain tissue as there are stars in the Milky Way,” to quote the
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