How Many Neurons Are in the Brain?

The typical human brain contains about 100 billion neurons. If it were possible to extract all of the neurons in a human brain and position them in a straight line, that line would extend for more than 620 miles (about 1,000 km). Neurons come in different lengths and sizes, with the average neuron being about 10 microns wide — meaning that a line of 1 million of them would be 32.8 feet (10 m) long. Also known as nerve cells, neurons are essential to the transporting of information to and from the brain.

More facts about brains:

• While still in the womb, a human fetus will grow about 8,000 new brain cells per second. A newborn infant will have all of the brain cells that he or she needs for a lifetime.


• A 2011 study published in the Journal of American Medicine indicated that children who suffer from autism have heavier brains that contain more neurons than the average person. Among various findings, the study noted that the prefrontal cortexes of autistic children held 67 percent more neurons than those of non-autistic children.


• The human brain contains about 60 percent white matter and 40 percent gray matter. The white matter contains the axons and dendrites that allow the neurons in the gray matter to send and receive information.