Glia

Unlike neurons, glial cells are not excitable and do not have any signaling apparatus (axons or synapses). Therefore, these cells do not participate in initiating the nerve impulse or in mediating activities of the nervous system. Their main function is to form myelin (which facilitates nerve conduction) and to support growth and differentiation of neurons. Glial cells, in relation to neurons, become increasingly numerous along the phylogenetic scale, and in mammals they constitute almost half the volume of the brain and greatly outnumber neurons by a ratio of approximately 10 to 1. Thus, as many as 100 billion glial cells are found in the human central nervous system (CNS).

Dendrites

Mitochondria

Lysosome

Dendrites

Mitochondria

Lysosome

Figure 1 Schematic drawing of a typical mammalian neuron (reproduced with permission of Chapman and Hall).

Nerve ending Synapse

Postsynaptic cell

Figure 1 Schematic drawing of a typical mammalian neuron (reproduced with permission of Chapman and Hall).

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