Synaptic Neurotransmission and the Anatomically Addressed Nervous System

• Neurodevelopment in the anatomically addressed nervous system
• Time course of neurodevelopment
• Neurogenesis
• Neuronal selection
• Neuronal migration
• Synaptogenesis: directing the axons and arborizing the dendritic trees
• Synaptic plasticity
• Competitive elimination of synapses
• Summary

Synaptic Neurotransmission and the Anatomically Addressed Nervous System

Modern psychopharmacology is largely the story of chemical neurotransmission. To understand the actions of drugs on the brain, to grasp the impact of diseases on the central nervous system, and to interpret the behavioral consequences of psychiatric medicines, one must be fluent in the language and principles of chemical neurotransmission. The importance of this fact cannot be overstated for the student of psychopharmacology. What follows in the next two chapters will form the foundation for the entire book and the road map for a journey through one of the most exciting topics in science today: the neuroscience of how drugs and disorders act on the central nervous system.

What is neurotransmission? It can be described in many ways: anatomically, chemically, electrically. This chapter (Chapter 2) describes the anatomical basis of neurotransmission by showing how neurons are the substrates of neurotransmission and how they develop, migrate, form synapses, and demonstrate “plasticity,” or the ability to morph and change throughout life. Classically, the central nervous system has been envisioned as a series of “hard-wired” synaptic connections between neurons, not unlike millions of telephone wires within thousands upon thousands of cables. Building on the structural and functional description of neurons in Chapter 1, this chapter emphasizes what is called the anatomically addressed nervous system. The anatomically addressed brain is thus a complex wiring diagram, ferrying electrical impulses to wherever the “wire” is plugged in (i.e., at a synapse). Following this discussion, the next chapter (Chapter 3) describes the chemical basis of neurotransmission by demonstrating how chemical signals are coded, decoded, transduced, and sent along their way.

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FIGURE 2-1 Time course of neurodevelopment. The time course of brain development is shown here. Most neurogenesis, neuronal selection, and neuronal migration occur before birth, although it has recently been discovered that new neurons can form in some brain areas even in adults. After birth, differentiation and myelination of neurons as well as synaptogenesis continue throughout a lifetime. Brain restructuring also occurs throughout life, but is most active during childhood and adolescence in a process known as competitive elimination.