| Model Neuron | Structural Variations | Naming Neurons | Organelles |
Naming Neurons
A number of conventions have evolved to classify and name neurons. One of the oldest, devised by Golgi in the late 1800’s, is based on the complexity of the dendritic tree of the neuron. Through this approach cells are classified as unipolar, bipolar and multipolar neurons as shown in Figure 8.8. Unipolar cells have only one cell process, and are primarily found in invertebrates. However, vertebrate sensory neurons are another form of this type of cell. Because these cells start out developmentally as bipolar neurons and then become unipolar as they mature, they are called pseudo-unipolar cells. Bipolar cells are present in the retina and the olfactory bulb. Multipolar cells make up the remainder of neuronal types and are, consequently, the most numerous type. These have been further sub-categorized into Golgi type II cells that are small neurons, usually interneurons, and Golgi type I cells that are large multipolar neurons.
Cells are also named for their shape (e.g., pyramidal cells shown in Figure 8.9) or for the person who first described them (e.g., Purkinje cells shown in Figure 8.10). More recently, cells have been named for their function or the neurotransmitter they contain (e.g., CNS norepinephrine cell groups covered in Chapter 12). This description is possible because of the development of histochemical and immunocytochemical methods to specifically identify the neurotransmitter type used by neurons.
