Neuroglia, or glial cells, are part of the nervous system that support neurons by providing them nutrients, oxygen and insulation and by eliminating harmful pathogens. They comprise approximately 15 per cent of the total cellular composition of the central nervous system, and are found in all regions of the spinal cord and brain.
According to "Neurocytology: Fine Structure of Neurons, Nerve Processes, and Neuroglial Cells", Schwann cells, or neurolemnocytes, are located in the peripheral nervous system (PNS). They play a supporting role in the nervous system by wrapping around nerve tissue and cells to form a protective myelin sheath (which is comprised of 80 per cent lipid and approximately 20 per cent protein). Schwann cells are involved in nerve regeneration, repair and development, the conduction of nerve impulses and the provision of antigens to T-lymphocytes (a type of WBC, or white blood cells, that play a role in cell immunity).
Satellite cells, or satellite glial cells (SGCs), surround neurons in the parasympathetic, sympathetic and sensory ganglia. The parasympathetic ganglia are a group of nerve cells that lie outside the central nervous system, and arise from the spinal cord. They are located in or around affected tissues and organs. Sympathetic ganglia form part of the sympathetic nervous system and are comprised of nerves that arise from the lumbar and thoracic regions of the spinal cord. They inform the body about impending danger and stress and prepare it for an appropriate fight-or-flight response. Sensory ganglia lie in the PNS and detect sensory receptors. Satellite cells are involved in muscular repair and regeneration.
According to "Neuroimmunoendocrinology," oligodendrocytes, or oligodendroglia, are part of the central nervous system (CNS) that function to provide support to nerves and axons. They produce an insulating myelin sheath that surrounds axons and allows them to function efficiently. Oligodendrocytes are divided into types I to IV.
Astrocytes are cells that are common to the spinal cord and brain. They function to supply nutrients to cells of the nervous tissue, maintain ion balance in extracellular cells, repair and regenerate damaged spinal cord and brain cells and support cells of the blood-brain barrier (endothelial cells). Astrocytes are divided into type 1 and type 2 cells by lineage and antigenic phenotype, and into protoplasmic, Gömöri-positive and fibrous astrocytes on the basis of anatomical classification.
Ependymal cells make up the ependyma, which are found in regions of the brain and spinal cord. They facilitate the unidirectional flow of the cerebral spinal fluid (CSF), which transports nutrients to the cells of the brain and removes toxic metabolites (by-products of metabolism).
Microglia are a type of neuroglia that reside in the spinal cord and brain. They function to provide immunity to nervous cells, engulf harmful foreign particles, repair damaged neural tissue and are involved in extracellular signalling. Microglia are the first stage of defence in the central nervous system.