The behavior of the neuron itself is more complicated than sending an axon pulse after receiving signal at a dendrite. The power consumption of the Pentium 4 may exceed that of the human brain. That explains why Pentium cooling systems are getting close in size to the human head. The number of transistors in 500 Pentiums is roughly the same as the number of neurons in cerebral cortex. The firing frequency is 1,000,000 times higher in the Pentium.
Transistors are less sophisticated than neurons.
For example, transistors cannot move and change connections. An introduction to genetic analysis. 1993 Molecular evolutionary genetics. Masatoshi Nei 1987 Role of excessive genetic information in evolution. Computer Analysis of Protein and Nucleic Acid Sequences.