![]() ![]() ![]() The profiles of some dendrites in the cortices of old monkeys show a cytoplasm devoid of organelles beyond a few microtubules beneath the plasma membrane ( Fig. Nevertheless, unusual images of dendrites that probably reflect the effects of age are sometimes encountered and some of these images are as follows:ฤก. Although no systematic studies have been made of the effects of age on the fine structure of dendrites, most profiles of dendrites in electron micrographs show no or few obvious age changes. It is known that with age dendrites, especially those in the apical tufts of pyramidal cells, retract and degenerate. Consequently profiles of their dendrites have more regular shapes and these dendrites receive most of their synapses on their shafts. In contrast to the dendrites of pyramidal neurons, the dendrites of nonpyramidal, inhibitory neurons have smoother outlines, with few or no dendritic spines. ![]() The dendritic spines receive the majority of axon terminals synapsing with dendrites of pyramidal and spiny stellate neurons, but electron microscopic images that show the entire lengths of dendritic spines are not commonly encountered and have to be sought. The dendrites of the excitatory pyramidal cells are also profusely decorated with dendritic spines so that profiles of their dendrites tend to have somewhat irregular outlines. They travel singly through the neuropil and have a cytoplasm that contains regularly spaced microtubules, ribosomes and rough endoplasmic reticulum, mitochondria, and long cisternae of smooth endoplasmic reticulum ( Figs. Dendrites are processes that extend from the cell bodies of cortical neurons. ![]()
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