The average number of neurons in the human brain is 100 billion - there are more nerve cells in the brain than there are stars in the Milky Way!

There are different theories. However, the most common is that once connections are made, myelin sheaths form around the axons, which send out inhibitory signals to growth.

250,000 neurons/minute.

Transmission speed of a axon depends on the diameter of the axon and if it is covered in a myelin sheath. Some large axons may transmit at speeds up to 90 metres (300 feet) per second.

There are 1,000 to 10,000 synapses for a "typical" neuron.

The cell bodies of neurons vary in diameter from 4 microns (granule cell) to 100 microns (motor neuron in spinal cord).