Neuroscience
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Axon

The other type of process in the idealized neuron is the axon. Each neuron has only one axon and it is usually straighter and smoother than the dendritic profiles. Axons also contain bundles of microtubules and neurofilaments and scattered mitochondria. The most MAPs in an axon have a lower molecular weight than those in the dendrite. A predominant MAP in axons is tau. Microfilaments within the axon are usually associated with an area adjacent to the plasmalemma and often are the most dense at the nodes of Ranvier. Beyond the initial segments, the axoplasm lacks rough endoplasmic reticulum and free ribosomes. The branches of axons are known as axon collaterales. The axon itself is often surrounded by a membranous material, called the myelin sheath, formed by glia cells. The myelin sheath acts to insulate the plasmalemma of the axon in a way that necessitates the more rapid spread of the depolarization of the plasmalemma and increases the speed of conduction of the nerve impulse (see Chapter 3).

Figure 8.5

Diagrammatic representation of the axon emphasizing the areas of microtubules, neurofilaments coursing within the cytoplasm.