Each cell, about 10 to the minus-6th power meter in diameter, contains a nucleus and branching fibers called dendrites and axons. These signals, or brain-wave patterns, are in the range of microvolts. Figure 1 shows two neurons with dendrite-axon contacts called synapses. During the first nine months of life, these neurons form at the astounding rate of 25,000 per minute. Two neurons are shown, representing the ten billion cells within the brain.
Axons are fibers that interconnect the cells.
The number of branching dendrites is large and variable. Each neuron is in dendritic contact with perhaps 10,000 other neurons. Actually, it is a much greater number, since the neurons also show intermediate firing states, somewhat like a light-dimmer switch. Consequently, the brain shows both digital and analog characteristics. This implies a rate of 10 to the 15th power signals or computations every second.