Neurons are composed of three basic parts: the cell body (soma or perikaryon); the dendrites, which receive information from other neurons; and a single axon, which conducts electrical impulses away from the cell body (Figure 1-2-1).
The cell body contains a large vesicular nucleus with a single prominent nucleolus, mitochondria, and other organelles. It has abundant RER, reflecting high rates of protein synthesis. At the light microscopic level, the RER stains intensely with basic dyes and is referred to as Nissl substance.
Microtubules and neurofilaments contribute to the neuronal cytoskeleton and play important roles in axonal transport. Pigment granules such as lipofuscin ("wear and tear" pigment) and melanin (found in some catecholamine-containing neurons) may be seen in the cytoplasm.
Dendrites are neuronal processes that receive information and transmit it to the cell body. Extensive dendritic branching serves to increase the receptive area of the neuron.
Axons are thin, cylindrical processes typically arising from the perikaryon (or from a proximal dendrite) through a short pyramidal-shaped region called the axon hillock. The cell membrane of the axon is called the axolemma, and the cytoplasm of the axon is called the axopiasm.
Axons contain abundant microtubules and neurofilaments. Axon fast transport uses microtubules. It proceeds in both anterograde and retrograde directions. Anterograde transport is powered by kinesins, whereas retrograde transport is powered by dynein.
Axons terminate in specialized endings known as synaptic boutons, which contain synaptic vesicles full of neurotransmitter.
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