Neurons

Abstract

Neurons are the cells that transmit information in the nervous system. To do this they have long extensions of the cell body that carry electrical signals and specialized contacts – synapses – where signals are transmitted between neurons. The exact shape and composition of these structures are critically important in determining how information is processed by the nervous system.

Keywords: axon; dendrite; synapse; cytoskeleton; morphology

Figure 1.

A large neuron in the cerebral cortex. This neuron has been made visible by silver staining using one of the oldest methods of neuroanatomy, the Golgi technique. It belongs to a class of large neurons in the cortex known as pyramidal cells because of the roughly pyramidal shape of their cell bodies. The black staining outlines the various branches of the dendrites as well as the single axon. At the higher magnification shown in the inset it can be seen that the dendrites are studded with large numbers of dendritic spines, which are the sites at which most of the synapses onto these cells are made. Bar, 25 μm.

Figure 2.

Different shapes of nerve cells reflect different functions. This silver‐stained preparation of mouse brain made by the Golgi technique shows two different types of neurons in the cerebellum that are located next to one another and make synapses. (a) Two Purkinje cells, very large neurons whose cell bodies are some 25 μm across and which have enormously extensive dendritic trees. (b) By contrast, the granule cell neurons, one of which is shown here, have cell bodies that are less than half the size of those of the Purkinje cells and their dendrites are limited to small, stubby protrusions. The long axons of the Purkinje cells are just visible before they run out of the microscope's focus, while the axon of the granule cell travels upwards into the zone of Purkinje cell dendrites, where it will form many synapses. Bar, 30 μm.

Figure 3.

Diagram of an excitatory synapse of the kind made onto both pyramidal cells in the cerebral cortex and Purkinje cells in the cerebellum. The transmitter substance molecules are represented by the small dots inside the synaptic vesicles and in the synaptic cleft into which they are released. They interact with receptor proteins that are bound into the postsynaptic density of the dendritic spine and are exposed on its surface. The overall size of such a synapse is around 1 μm. In this drawing the sizes of some of the components have been exaggerated for clarity, in particular the vesicles are drawn disproportionately large and the synaptic cleft is disproportionately wide.

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Further Reading

Levitan IB and Kaczmarek LK (1997) The Neuron: Cell and Molecular Biology, 2nd edn. New York: Oxford University Press.

Peters A, Palay SL and Webster H deF (1991) The Fine Structure of the Nervous System, 3rd edn. New York: Oxford University Press.

Purves D and Lichtman JW (1985) Principles of Neural Development. Sunderland, MA: Sinauer Associates.

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How to Cite close
Matus, Andrew(Apr 2001) Neurons. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000282]