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Neurons

A view of nervous tissue will always show neurons with a variety of supportive cells called neuroglia.  Keep in mind, the only conductive cells(those sending impulses) are neurons.  Neuroglia perform other functions within the nervous system.

Neurons occur in three varieties.  These include:

  1. multipolar types-the majority of neurons
  2. bipolar types-sensory neurons found in the special senses
  3. unipolar types-sensory neurons located in dorsal root ganglia

All three types are large, three-dimensional cells with long processes.  For this reason, it is unlikely you will see an entire neuron with all of its parts.  Depending on the section and the location, only parts of neurons are visible at any given time.

For example, these are unipolar sensory neurons of a dorsal root ganglion.  Satellite cells are the smaller supportive cells visible around the large nuclei of the unipolar neurons.  Processes of these neurons cannot be seen in this view.

Multipolar Neurons

Since the majority of neurons are multipolar, this is the type used to illustrate parts and functions of a typical neuron.

Key functional components of neurons shown here are the dendrites and axons.  Dendrites collect impulses from other neurons.  These impulses summate on the perikaryon or nucleus and if sufficient in strength, generate output along the axon. Within the CNS axons terminate near dendrites of other neurons in synapses.  If axons of CNS neurons carry output to muscles or glands, these pass through nerves of the PNS or peripheral nervous system.  Follow the arrows in the diagram to see typical motor output to effectors.

Note the cell body of the neuron is typically found in the CNS.  When you are examining  most tissues, you are looking at structures outside the CNS.  Therefore, if you see nervous tissue here it will most often be receptors, nerves, or axon terminals.  This is why smears or sections of the spinal cord are typically used to show multipolar neuron cell bodies.  In the PNS, the only locales with neuron cell bodies are ganglia or organs of the special senses.

Now, let's take a look at some nervous tissues!

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