NEUROGLIA – 1
Neuroglia consists of a large population of cells called neuroglial cells, or simply glial cells. They perform important functions in the support, protection, and metabolic maintenance of the central nervous system (CNS).
Unlike neurons, neuroglial cells do not generate or transmit nerve impulses along their processes.
Neuroglial cells are found throughout the central nervous system. The peripheral nervous system contains other types of supporting cells that perform functions comparable to those of neuroglial cells. Some authors include these cells within the neuroglia, whereas others classify them separately.
The following pages describe the main types of neuroglial cells found in the central nervous system:
Astrocytes are cells with numerous cytoplasmic processes. They provide structural and metabolic support to neurons and extend processes around blood vessels. These processes contribute to the blood-brain barrier, which regulates the movement of substances between the blood and nervous tissue.
Two main types of astrocytes are recognized: protoplasmic astrocytes and fibrous astrocytes. Protoplasmic astrocytes are found mainly in the gray matter of the central nervous system. Fibrous astrocytes are found mainly in the white matter and have fewer and longer processes.
Oligodendrocytes are found in both the gray and white matter of the central nervous system. They are particularly numerous in the white matter, where many neuronal processes are present. Oligodendrocytes form the myelin sheaths around axons in the central nervous system.
Microglia consists of specialized microglial cells with phagocytic properties. They participate in the immune defense and maintenance of nervous tissue.
This and the next pages will deal with the neuroglial cell types of the central nervous system:
Astrocytes, are cells with many cytoplasmic processes that support and help the nourishment of neurons and enfold blood vessels providing part of the blood-brain barrier that regulates the traffic of substances that may enter the brain tissue.
There are two types of astrocytes, the protoplasmic and the fibrous astrocytes.
The protoplasmic astrocytes reside mainly in the gray matter of the central nervous system. Fibrous astrocytes are found mainly in the white matter. They have less and longer processes.
Oligodendrocytes are found in the gray matter of the central nervous system and in a greater amount in its white matter where more neuronal processes are present.
The microglia is formed by the microglial cells. They have phagocytic properties and participate in the immunological protection of the nervous tissue.
It is not easy to recognize and distinguish the different types of neuroglial cells in routine paraffin sections stained with conventional histological stains. For this reason, several techniques were developed in the past to demonstrate these cells, including metal impregnation techniques, in which metal is deposited on the cells and their processes.
The results of metal impregnation techniques can be difficult to control. Sometimes, excessive amounts of metal are deposited on the cells, obscuring their structure. In addition, these techniques do not reveal the internal details of the nucleus and cytoplasm.
Today, immunocytochemical methods are widely used to identify and distinguish the different types of neuroglial cells in tissue sections. These methods use antibodies that recognize specific proteins expressed by particular types of neuroglial cells, allowing them to be identified more reliably.