![]() Contact with afferent fibers or with target cells during the period of process outgrowth is unnecessary for the expression of these features of axonal and dendritic differentiation. ![]() These observations show that the fundamental differences in form and in the distribution of ribosomes between axons and dendrites can be established in cell culture. The axons most commonly arose from the proximal portion of a dendrite rather than directly from the cell body as they typically do in situ. Clusters of polyribosomes were invariably present at dendritic branch points, but they were never observed at axonal branch points. These ultrastructural differences were particularly obvious at branch points, where cytoplasmic organelles tend to accumulate. Axons, which were several times longer than the dendrites, were thinner at the origin, tapered much less, and were essentially ribosome-free. Dendrites were rather thick at the base but tapered rapidly to a minimum diameter of about 0.5 micron and contained polyribosomes throughout their length. Dendrites and axons could be clearly distinguished by both light and electron microscopy. Examples of such isolated cells which had developed for 1 week in culture were studied first by light microscopy, then they were sectioned parallel to the substratum so that all portions of the cell and its processes could be examined by electron microscopy. Under such conditions, some cells develop without contacting any neighboring neurons or glial cells. In c, a new spine is making a synapse with a bouton that also has a synapse with a second spine. Pseudounipolar sensory neurons have an oval-shaped cell body and a long dendrite and an axon that have fused forming a long axon as shown in Figure 9. If the chemical signal crosses the synapse to another neuron. Nerve cells, which were obtained from fetal rats at 18 to 20 days of gestation, were plated at very low density onto polylysine-treated coverslips and were maintained in serum-free medium. In a and b, two new spines with the same parent dendrite are making synapses with the same axon. a small gap (called the synapse) to be released to the next neuron or a muscle cell. We have studied the processes which are elaborated by hippocampal neurons in dissociated cell culture. In addition to the above neuron classification scheme more recent schemes use connectivity patterns and quantitative morphology (cell body, dendrites and axons) together with biophysical and. ![]()
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