Neuroglia is the collective term for glial cells, specialized cells that protect and regulate the functioning of neural cells in the brain. In addition to promoting electrical communication between nerve synapses, some of these cells physically protect neural cells by surrounding them to form an insulating barrier. Other cells of this type are involved in the delivery of oxygen and other nutrients, while still others play a role in targeting and eliminating invading pathogens. The name “glial” is taken from the Greek word glia, which literally means “glue,” indicating their significant contribution in the performance of the central and peripheral nervous systems.
There are six distinct types of neuroglia cells, four of which reside in the central nervous system. Oligodendrocytes surround and protect neural cells by forming a barrier known as the myelin sheath. Ependymal cells are active in the lining of the network of fluid-filled ventricular cavities found in the brain and spinal cord. Astrocytes regulate the exchange of nutrients between blood vessels and neural cells, while microglia scavenge and destroy cellular pathogens and other debris.
In the peripheral nervous system, neurolemmocytes perform the same duty as oligodendrocytes in terms of forming the protective myelin sheath surrounding neurons. These neuroglia cells are also known as Schwann cells, and are capable of initiating the repair or regrowth of neural axons and dentrites that have become damaged due to trauma or injury. Lastly, satellite neuroglia cells inhabit the ganglion tissue that envelop and support neural cells.
Collectively, neuroglia regulate a variety of biological processes to ensure that certain conditions remain balanced and constant in the body, a state known as homeostasis. For instance, some glial cells focus on regulating certain internal conditions in order to maintain proper functioning in response to changing external environmental conditions, such as temperature. These cells also assist in the regulation and metabolism of glucose, insulin, and other pancreatic enzymes. A unique characteristic of neuroglia cells is that they are capable of cellular division after reaching maturity, while the majority of neural cells lose this ability at some point in their development.
While the total number of glial cells in the human brain closely equals the number of neurons, they outnumber neurons in some parts of the brain by up to 50 times. Brain size also determines the number of cerebral neuroglia. Therefore, different species of animals contain varying concentrations of glial cells. The brain of a fruit fly, for example, is composed of 24 percent glia, compared to 90 percent in a human and 97 percent in an elephant.