Cells {glia}| can provide neuron covering and environment.
covering
Glia cover nerve surfaces, except at synapses and nodes of Ranvier.
structure
Glia provide paths for migrating neurons.
properties
Glia are contractile. Glia can divide. Glia do not conduct. Glia do not interact electrically with neurons. Perhaps, glia are polarizable [Cornell-Bell et al., 1990] [Laming et al., 1998] [Sanderson, 1996].
types
Oligodendrocytes and astrocytes are macroglia. Macrophages are microglia.
chemicals
Glia make myelin, which surrounds axons. Glia make amino acids for neurons. Glia maintain extracellular fluid chemical concentrations. Glia have cholinesterase, whereas neurons have acetylcholinesterase. Glia have much less RNA than neurons.
chemicals: synapses
Glia respond to ATP that leaves synapses by letting calcium in and changing proteins made. Astrocytes make thrombospondin, which builds synapses.
chemicals: regulation
Glia and neuron membranes, receptors, and chemicals interact. Glia regulate extracellular ion, neurotransmitter, and other small-molecule concentrations. Glia can release reactive oxygen molecules, nitric oxide, prostaglandins, excitatory amino acids, IL-1, and nerve growth factor. Excitatory amino acids are N-methyl-D-aspartate and non-NMDA agonists. These can excite pain-responsive spinal cord neurons and increase neurotransmitter release from nerves that relay pain information to spinal cord.
chemicals: factors
Substances released by neurons affect glia [Araque et al., 1999] [DeLeo and Yezierski, 2001] [Raghavendra and DeLeo, 2003] [Watkins et al., 2001].
numbers
Human brains have nine glial cells for every neuron. Glia-to-neuron ratio is as much as 20-to-1 in humans. Glia are half of brain mass. Rats have four or five glial cells for each neuron. The higher human glia-to-neuron ratio reflects need for more chemical and electrical environments and neural connections [Araque et al., 1999] [DeLeo and Yezierski, 2001] [Raghavendra and DeLeo, 2003] [Watkins et al., 2001].
Macroglia {astrocyte} can be protoplasmic, with branched processes, or fibrous, not branched. They cover blood vessels, neurons, and external brain surfaces. They provide structure and guides neuron migration. They take up potassium ions and neurotransmitters. Some astrocytes repair nervous tissue. Astrocytes affect metabolic disorders and epilepsy.
Glia membranes {blood-brain barrier}| (BBB) {glial membrane} can surround nervous-system blood vessels, delay sodium and potassium ion passage, and block passage of other ions and molecules. BBB is interface between blood capillaries and brain tissue.
Glia connect by gap junctions {gap junction, glia}. Electrical stimulation can spread rapidly through connected glia [Araque et al., 1999] [DeLeo and Yezierski, 2001] [Raghavendra and DeLeo, 2003] [Watkins et al., 2001].
oligodendrocytes or astrocytes {macroglia}.
Central nervous system macrophages {microglia} absorb and digest dead cells. They also receive signals from immune cells. They can react to pathogens. Perhaps, they can receive signals from viruses and damaged nerves. They do not affect normal pain responses but can cause abnormally high pain when they receive signals from immune cells [Kreutzberg, 1996] [Meller et al., 1994] [Watkins et al., 2001]. Astrocytes become active when microglia become active.
Microglia make surface receptors {microglia receptor} for macrophage antigen complex-1 (Mac-1), phagocytosis, and cytotoxic-molecule production, including reactive oxygen molecules, nitric oxide, prostaglandins, and proinflammatory cytokines such as interleukin (IL) and tumor necrosis factor (TNF) [Hopkins and Rothwell, 1995].
Macroglia {oligodendrocyte} makes myelin and wraps from several to 50 axons. Oligodendrocytes affect multiple sclerosis and spinal cord injury.
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Date Modified: 2022.0225