Some features of dendrites
a. Dendrites can be distinguished immuno-cytochemically from axons because of the presence in them of microtubule associated protein MAP-2 not present in axons.
b. Dendritic spines vary in size and shape. Some spines contain aggregations of smooth endoplasmic reticulum (in the form of flattened cisternae with associated dense material). The complex is referred to as the spine apparatus.
c. Actin filaments are present in dendritic spines.
d. Some variations in the dendritic field are as follows. The field may be spherical (as in stellate cells), hemispherical,disc-like,conical or flat. In some neurons (e.g., pyramidal), the neuron may have two separate dendritic fields. Apart from shape there is considerable variability in extent of the dendritic field. Some neurons (e.g., Golgi neurons of the cerebellum) have dendritic fields covering a very wide area. More than eighty per cent of the neuronal surface area (excluding the axon) may be situated on the dendritic tree. The frequency of branching of dendrites is correlated with the number of synapses on them. In some neurons the dendritic spines may number several thousand. Finally, it may be emphasised that the dendritic tree is not a ‘fixed’ entity, but may undergo continuous remodelling. This affords a basis for modification of neuronal behaviour.
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