Other dystrophic axons contain neurofilaments intermingled with organelles that are elongate structures with moderately electron dense, thick walls surrounding a lucent core. Yet other dystrophic myelinated axoplasmic accumulations contain neurofilaments intermixed with lysosomes ( Figs. Other dystrophic axons have a cytoplasm with a core of neurofilaments surrounded by accumulations of lysosomes and mitochondria ( Fig. Some dystrophic axons contain what appear to be accumulations of neurofilaments. 4.7, 4.7A, and 4.8).Įxamples of dystrophic axons that contain accumulations of organelles are shown in the following:ġ. It is assumed that these alterations eventually lead to the complete degeneration of the axon, resulting in the production of empty myelin sheaths ( Figs. 4.5), ultimately leading to darkening to the axoplasm ( Fig. 4.1, 4.2, 4.3, 4.3A and 4.4), and sometimes accumulations of neurofilaments ( Fig. The beginning of degeneration of some axons is characterized by an accumulation of mitochondria and lysosomes in the axoplasm ( Figs. Some 20 to 40% of myelinated nerve fibers are lost from fiber tracts with age, so that nerve fibers with altered axons in various stages of degeneration are encountered in electron micrographs, especially those from old monkeys. A different set of alterations lead to the degeneration of the myelin sheaths and ultimately the remyelination of the axon. Some nerve fibers undergo degeneration that is initiated by the degeneration of the axon. Myelinated nerve fibers undergo a variety of alterations with age.
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