What is the role of glial cells in the human body?

Glial cells are important cells in the human body, distributed between neurons, forming a mesh scaffold that helps protect our health. Many people usually test glial cells when they go to the hospital to check for neurological diseases. If the amount is small or large, or if there are abnormal manifestations, this will affect the normal functioning of our neurons. Because glial cells support the nutrition and protection of neurons, as well as the formation and repair of multiple functions, you should understand them carefully during the examination.

Introduction

There is another type of cell in the central nervous system, namely glial cells, or glial cells for short. Glial cells are about 10 to 15 times the size of neurons, and their total volume is almost the same as that of neurons (neurons account for about 45% and glial cells account for about 50%). In conventional neural tissue sections, glial cells are usually smaller in size than neurons.

Classification

1. Central nervous system: mainly includes astrocytes (fibrous astrocytes, protoplasmic astrocytes), oligodendrocytes, microglia, ependymal cells, perivascular membrane cells, choroid plexus epithelial cells, Bergmann glial cells, Müller cells, pituitary cells and extensor cells.

2. Periphery: Schwann cells and satellite cells.

Both glial cells and neurons originate from the neuroepithelial tissue of the ectoderm of the germinal disc (microglia may originate from the mesoderm). The glioblasts develop into macroglia and choroid plexus epithelial cells, some neuroepithelial cells surrounding the surface of the neural tube lumen differentiate into ependyma and choroid plexus epithelial cells, neuroblasts develop into neurons, and the neural crest differentiates into glial cells of the peripheral nervous system.

Astrocytes

The largest glial cells have a cell body diameter of 3 to 5 microns, a spherical nucleus that is often located in the center and lightly stained. It has many long protrusions, one or several of which extend to the adjacent capillaries. The ends of the protrusions swell to form vascular foot processes, forming a layer of glial membrane around the endothelial basement membrane of the blood vessels. Some astrocyte processes are also attached to the underlying membrane of the pia mater and ependyma of the brain and spinal cord, separating the pia mater, ependyma and neurons. Astrocytes are divided into two types: protoplasmic and fibrous. Protoplasmic astrocytes are often found in gray matter. They have thicker and more branched processes, which are thin plate-like and surround the neuron cell bodies and the parts of the dendritic surface that are not covered by synapses, with small gaps between them and the neuron cells. The processes of fibrous astrocytes are long and smooth, with not many branches. There are many fibril-like substances in the cytoplasm of the cell body and processes, which are integrated into bundles of varying sizes. Electron microscopic observations showed that the protoplasmic and fibrous astrocytes contained the same organelles in the cytoplasm around the nucleus and in the large processes, as well as obvious glycogen granules and cytoplasmic fibrils, indicating that the two types may belong to the same type of glial cells. Some people believe that under abnormal conditions, astrocytes can proliferate through mitosis and amitosis due to damage or stimulation. However, astrocytes near the damaged part of the mouse cerebral cortex do not take up 3H-labeled thymidine, so cell proliferation cannot be confirmed.

Oligodendrocytes

They are smaller than astrocytes, with a diameter of 1 to 3 microns. Their processes are fewer and shorter than those of other glial cells, resembling beads. They have no vascular feet and do not produce fibers in the cytoplasm, but they have more mitochondria than astrocytes. Oligodendrocytes are found in both gray matter and white matter. In the gray matter, they are located close to neurons and are called satellite cells. Oligodendrocytes are the largest group of cells found in each neuron of the human central nervous system. Neuronal satellite cells increase in number in response to injury and can phagocytose their own myelin degeneration products. Oligodendrocytes occur in rows between myelinated fibers in the white matter. The myelin sheath of the central nervous system is formed by processes of oligodendrocytes, and therefore has the same function as Schwann cells of the peripheral nerves. An oligodendrocyte can form a sheath (up to 20) between the nodes of multipolar nerve fibers with its different processes. Oligodendrocytes have small, round nuclei with dense chromatin, high electron density cytoplasm containing mitochondria, ribosomes and microtubules, which make them identifiable in electron micrographs. Oligodendrocytes have been observed to exhibit periodic and vigorous movements in tissue culture.

Microglia

The body is small, dense and oblong or oval. The chromatin in the nucleus is very dense, and the nucleus is also long along the long axis of the cell body. Microglia are distinctive in hematoxylin-eosin stained sections; their processes are short and densely covered with numerous branchlets that resemble thorns. Although the number of microglia is small, they are present in both gray and white matter. The number in gray matter is 5 times that in white matter. The number of microglia in the hippocampus, olfactory lobe and basal ganglia is more than that in the thalamus and hypothalamus, and the least in the brainstem and cerebellum. Some of the phagocytic microglia apparently derive from hematopoietic monocytic stem cells rather than from neural origin, and many invading phagocytes appear after injury. Under normal circumstances, astrocytes have the phagocytic function of clearing cellular debris.