Med. Sci. 532

NEURONS AND NEUROGLIA
Neuroglial cells, the other major cell type in neural tissue, provide structural integrity to the nervous system and functional support that enables neurons to perform.

The word 'neuroglia' (nerve glue) was introduced by Rudolf Virchow about 1854.

 Neuroglia do not typically have synapses at their surface.  Classically neuroglial cells are described as existing only in the central nervous system (CNS, i.e. brain and spinal cord) where there are three kinds:

i.    astrocyte (dark green)
ii.   oligodendrocyte (light green)
iii.  microglia (blue)
Astrocytes, known for the many processes attached to their cell body, provide structural support and their processes often have 'end feet' that abut the basal lamina around the capillary endothelium or line the exterior surface of the CNS, where they contribute to the pial-glial external limiting membrane.  Cell bodies of astrocytes are among the largest for the glia, but only overlap the lower end for size of neurons.  
Oligodendrocytes form myelin sheaths around axons in the CNS.  One oligodendrocyte can form myelin sheaths along more than one internode of more than one axon.  They have smaller cell bodies than astrocytes and relatively fewer processes leaving the cell body.
The electron micrograph shows the cell body of an oligodendrocyte. Its nucleus is at the upper right and processes extend around myelinated fibers toward the lower left.  The relatively electron dense cytoplasm is characteristic.
Microglia are the main phagocytic cell and antigen-presenting cells in the CNS.  They have the smallest cell bodies among the neuroglia.
There are at least two other cells in the adult mammalian CNS that could be considered 'glial-like cells'
Ependymal cells line most of the ventricular system of the CNS, which is an inner space or lumen.  At least seven of them with nuclei are evident in this electron micrograph of spinal cord.  The lumen/central canal is at upper right.
Choroidal cells form the inner layer of the choroid plexus which abuts the ventricular system at certain places in the brain.  These cells secrete cerebrospinal fluid into the ventricles.
The phrase 'neuroglial-like' is also used to account for cells found in the peripheral nervous system (PNS) that are not neurons and that have functions similar to the classically described neuroglia.
Schwann cells form myelin (one Schwann cell/internode/axon) in the PNS. In the photomicrograph, their nuclei are the dark, cigar-shaped structures among the myelinated fibers that occupy the center and bottom parts of the picture. 
Satellite (capsule) cells surround cell bodies of neurons in ganglia (both sensory and autonomic ganglia, but especially the former). Their nuclei are the dark, round structures that surround the neuronal cell bodies at the top and right sides of the picture.
Neurocytology
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