Neuroglia

Neuroglial cells are the supportive cells of nervous tissue. They outnumber neurons about 10 to 1. Like neurons, glial cells are composed of cell bodies and cell processes. (Note: Glial processes are visible only in special stained preparations, such as a Golgi stain.)

Three major types of neuroglial cells are recognized in the central nervous system:
      (a) astrocytes -- provide structural & functional support for the CNS;
      (b) oligodendroglia -- form myelin in the CNS, and
      (c) microglia -- serve as a macrophage in the CNS.

Astrocytes:

On glass slide 49 in your Histology slide box, cerebral cortex of dog (Golgi stain), search for astrocytes such as those illustrated below.

Fig. 4. Two astrocytes and blood vessel profiles (V) are visible in this Golgi stain. Astrocytes have processes that may be long, slender, and relatively unbranched (in white matter) or short and highly branched (in gray matter). Note: The extensive perikaryon-free portion of the cerebral cortex is comprised of neuropil which includes the processes of both neurons and neuroglial cells.

Oligodendrocytes:

On glass slide 49 in your Histology slide box, cerebral cortex of dog (Golgi stain), search for ologodendrocytes such as those illustrated below.

Fig. 5. Several oligodendroglial cells are shown above in a Golgi stain. Oligodendrocytes are considerably smaller than astrocytes and have fewer cell processes. The perikarya are round and dark. Relatively few cell processes emanate from an oligodendrocyte cell body.

On glass slide A-1 in your Neuroanatomy slide box, canine spinal cord, search the white matter for astrocyte and ologodendrocyte cell bodies as they appear in routine stains, illustrated below.

Fig. 5. Luxol blue (top) and H&E (bottom) stains of spinal white matter. Cell bodies in white matter belong to glial cells (or blood vessels) not to neurons. An astrocyte cell body (green arrow) can be recognized by its relatively large, oval, leptochromatic nucleus. An oligodendrocyte cell body (red arrow) features a small, round, pachychromatic nucleus. In routine stains, glial processes are not visible. (Small black arrows point to axon profiles within vacuoles left by myelin lipid extraction during tissue processing.)

Microglia:

Microglia are difficult to find. Microglial cells have small elongate perikarya and short cell processes. They comprise only about 4% of the glial cell population under normal circumstances. An example of a microglial cell will be on demonstration in the laboratory.

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