The 100 billion neurons in the brain share a number of common features (Figure 1). These nanocircuits constitute the underlying biochemical machinery for mediating key neuronal properties such as learning and memory and the genesis of neuronal rhythmicity.
Networks are also prevalent within neurons. So, multiple levels of networks are ubiquitous in the nervous system. Macrocircuits mediate higher brain functions such as object recognition and cognition. More complex networks ( macrocircuits) consist of multiple imbedded microcircuits. Just a few interconnected neurons (a microcircuit) can perform sophisticated tasks such as mediate reflexes, process sensory information, generate locomotion and mediate learning and memory. Synaptic transmission comes in two basic flavors: excitation and inhibition.
To understand neural networks, it is necessary to understand the ways in which one neuron communicates with another through synaptic connections and the process called synaptic transmission. What makes the nervous system such a fantastic device and distinguishes the brain from other organs of the body is not that it has 100 billion neurons, but that nerve cells are capable of communicating with each other in such a highly structured manner as to form neuronal networks. This chapter will begin with a discussion of the neuron, the elementary node or element of the brain, and then move to a discussion of the ways in which individual neurons communicate with each other. Fortunately, much is known about the properties of individual neurons and simple neuronal networks, and aspects of complex neuronal networks are beginning to be unraveled.
Its phenomenal features would not be possible without the hundreds of billions of neurons that make it up, and, importantly, the connections between those neurons. The three pounds of jelly-like material found within our skulls is the most complex machine on Earth and perhaps the universe.
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