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NEUROSCIENCE OF PSYCHOACTIVE SUBSTANCE USE AND DEPENDENCE

Fig. 2.8 Structure of a neuron

Terminal button
Synaptic vesicles

Cell membrane Synapse
Nucleus
Node of Ranvier
Cytoplasm
Axon
Cell body Myelin
sheath
Axon hillock
Axodendritic synapse
Dendrite
Axosomatic synapse

Unmyelinated axons

Source: Reproduced from Pinel, 1990, with permission from the publishers.

Cell body
The cell body, or soma, is the metabolic centre of the neuron, and contains
the nucleus and other structures that sustain the neuron. A specialized
membrane that helps to regulate the internal environment of the cell
surrounds the cell body. It is selectively permeable in that it allows only certain
molecules into or out of the cell body, in order to maintain the proper
functioning of the cell.
By definition, the cell body is the part of the neuron that contains the
nucleus (Fig. 2.9). The nucleus contains the genetic material deoxyribonucleic
acid (DNA). DNA is used in cell division and growth, but also plays a role in
mature neurons, where it is used to synthesize proteins in response to a wide
variety of stimuli. Psychoactive substances can affect the expression of DNA,
resulting in short-term or long-term changes in neuronal function, and
ultimately, behaviour. This will be discussed in more detail at the end of the
chapter.

Dendrites
Dendrites are highly branched processes extending from the cell body of the
neuron, that receive chemical messages from other neurons (see Fig. 2.8).
This branching, and the presence of dendritic spines (small swellings on the

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