Our aim in this chapter is to consider how what we now know of the nervous system may account for understanding human behavior. Rather than the early view of animal spirits and surrogates for them, our view of the nervous system is that it is composed of neurons, with a mechanism of axoplasmic transport in them as schematized for a peripheral neuron in Figure 16.1. The same axonal mechanism is present as well in all neurons in the central nervous system. An example is that of cortical neurons crossing from one hemisphere to the other via the callosal tract. In addition to components required to maintain the viability of fibers and to provide the neurotransmitters acting at synaptic junctions. Other molecular signals are transported between neurons to establish and maintain the networks responsible for the integrated behavior of the organism. Networks formed in the brain under genetic control are responsible for perception, cognition and memory and are not permanently fixed. They are modified in the course of learning (Chapter 15). The broader theoretical issues relate to the degree of innateness of sensory and perceptual processes and how change is brought about.

Up through most of the latter century, the concept of reflexes was held as the key to understanding behavior. In his great book on reflexes of the nervous system, Sherrington wrote,