Function

The neuron is the basic functional cellular unit of nervous system operations; it is the principal investigational target of research into the actions of addictive drugs and ALCOHOL. An essential feature of the cellular composition of the brain is the high density of extremely varied, heterogeneously shaped neuron groups (see Figure 1). To understand the specialized aspects of neurons and their

Figure 1

Neuronal Complexity. The complexity of the neuronal network in the brain is demonstrated by this bundle of neurons, which form a vast and ramified structure with their cell bodies, outgrowths, and intercellular contact points.

SOURCE: Modified from Figure 1, in M. J. Kuhar's Introduction to Neurotransmitters and Neuroreceptors, in Quantitative Imaging, edited by J. J. Frost and H. N. Wagner. Raven Press, New York, 1990.

Figure 1

Neuronal Complexity. The complexity of the neuronal network in the brain is demonstrated by this bundle of neurons, which form a vast and ramified structure with their cell bodies, outgrowths, and intercellular contact points.

SOURCE: Modified from Figure 1, in M. J. Kuhar's Introduction to Neurotransmitters and Neuroreceptors, in Quantitative Imaging, edited by J. J. Frost and H. N. Wagner. Raven Press, New York, 1990.

function, therefore, requires a discussion of the general structural and functional features characteristic to all neurons and the degree to which unique variations form consistent subsets of neurons.

Neurons share many cellular properties that distinguish them significantly from other cell types in other tissues; those changes within the cell's regulatory processes of greatest interest to researchers of addictive drugs, however, depend on features that form distinctions within the class of cells called neurons. Furthermore, the assembly of individual neurons into functional systems, through highly precise circuitry employing highly specified forms of chemical interneuronal transmission, allows for the sensitivity of a brain to addictive drugs.

In some organs of the body—such as the liver, kidney, or muscle—each cell of the tissue is generally similar in shape and function. Within that tissue, all perform in highly redundant fashion to convert their incoming raw material into, respectively, nutrients, urine, or contractions, which establishes the function of the specific tissue. In the nervous system, the variously (heterogeneously) shaped neurons (see Figure 2), supported by an even larger class of similarly (homogeneously) shaped non-neuronal cells, termed neuroglia, convert information from external, or from internal, sources into information ultimately integrated into programs for the initiation and regulation of behavior.

This integrative conversion of sensory information into behavioral programs results from the rich interconnections between neurons, and it depends on the extremely differentiated features of neu-rons—their size and shape; their extended cell-surface cytoplasmic processes (dendrites and axons); and their resultant interconnections that establish the sources of their incoming (afferent) information

Figure 2

Three Types of Neurons

Figure 2

Three Types of Neurons and the targets of their outgoing (efferent) communication (see also Figure 4).

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