Nervous Tissue Glial Cells

Neuroglia, also called glia or glial cells, are non-neuronal cells of the nervous system. They compose a rich support system that is essential to the operation of nervous tissue and the nervous system. Unlike neurons, glial cells do not have axons, dendrites, or conduct nerve impulses. Neuroglia are typically smaller than neurons and are about three times more numerous in the nervous system. Glia perform a number of functions in the nervous system, including physically supporting the brain; assisting in nervous system development, repair, and maintenance; insulating neurons; and providing metabolic functions for neurons. Types of Glial Cells There are several types of glial cells present in the central nervous system (CNS) and peripheral nervous system of humans. They each serve different purposes for the body. The following are the six main types of neuroglia. Astrocytes Astrocytes are found in the brain and spinal cord and are 50 times more plentiful than neurons and the most abundant cell type in the brain. Astrocytes are easily identifiable due to their unique star-shape. The two main categories of astrocytes are protoplasmic and fibrous. Protoplasmic astrocytes are found in the gray matter of the cerebral cortex, while fibrous astrocytes are found in the white matter of the brain. The primary function of astrocytes is to provide structural and metabolic support to neurons. Astrocytes also aid in transmitting signals between neurons and brain blood vessels to control the intensity of blood flow, though they do not do the signaling themselves. Other functions of astrocytes include glycogen storage, nutrient provision, ion concentration regulation, and neuron repair. Ependymal Cells Ependymal cells are specialized cells that line the cerebral ventricles and central canal of the spinal cord. They are found within the choroid plexus of the meninges. These ciliated cells surround capillaries of the choroid plexus. Functions of ependymal cells include CSF production, nutrient provision for neurons, filtration of harmful substances, and neurotransmitter distribution. Microglia Microglia are extremely small cells of the central nervous system that remove cellular waste and protect against the invasion of harmful microorganisms such as bacteria, viruses, and parasites. Because of this, microglia are thought to be a type of macrophage, a white blood cell that protects against foreign matter. They also help to reduce inflammation in the body through the release of anti-inflammatory chemical signals. Additionally, microglia protect the brain by disabling malfunctioning neurons that become injured or diseased. Satellite Cells Satellite glial cells cover and protect neurons of the peripheral nervous system. They provide structure and metabolic support to sensory, sympathetic, and parasympathetic nerves. Sensory satellite cells are often linked to pain and sometimes even said to be associated with the immune system. Oligodendrocytes Oligodendrocytes are central nervous system structures that wrap around some neuronal axons to form an insulating coat known as the myelin sheath. The myelin sheath, composed of lipids and proteins, functions as an electrical insulator of axons and promotes more efficient conduction of nerve impulses. Oligodendrocytes are generally found in the brains white matter, but satellite oligodendrocytes are found in gray matter. Satellite oligodendrocytes do not form myelin. Schwann Cells Schwann cells, like oligodendrocytes, are neuroglia that create the myelin sheath in peripheral nervous system structures. Schwann cells help to improve nerve signal conduction, nerve regeneration, and antigen recognition by T cells. Schwann cells play a vital role in nerve repair. These cells migrate to the site of injury and release growth factors to promote nerve recovery, then myelinate newly generated nerve axons. Schwann cells are being heavily researched for their potential use in spinal cord injury repair. Both oligodendrocytes and Schwann cells indirectly assist in the conduction of impulses, as myelinated nerves can conduct impulses quicker than unmyelinated ones. White brain matter gets its color from large numbers of myelinated nerve cells. Sources Purves, Dale. â€Å"Neuroglial Cells.†Ã‚  Neuroscience | 2nd Edition, U.S. National Library of Medicine, 2001.Sofroniew, Michael V., and Harry V. Vinters. â€Å"Astrocytes: Biology and Pathology.†Ã‚  SpringerLink, Springer-Verlag, 10 Dec. 2009.