Neuroglia

Neuroglia - Cells that provide metabolic support and immune protection for neurons. Neuroglia outnumber neurons by about 10:1 in the Central Nervous System. Neuroglia do not generate or conduct nerve impulses. However, unlike neurons, glial cells can regenerate if injured

Astrocytes - Provide for the energy and other metabolic needs of neurons as well as giving nervous tissue structural support. When neurons of the brain or the spinal cord are injured and destroyed, they are replaced with scar tissue made up of astrocytes (a process called gliosis).

Microglia - Phagocytic cells, similar to macrophages, that perform a housekeeping function by removing dead cellular material and bacteria from the CNS.

Ependymal Cells - Cells that line the cerebral spinal fluid (CSF) containing cavities of the brain - the ventricles. CSF is secreted by a specialized subset of ependymal cells in the walls of the ventricles of the brain called the choroid plexus.

Oligodendrocytes - Cells responsible for myelination of axons within the Central Nervous System.

The dendrites and axons of sensory neurons and motor neurons that lie outside of the central nervous system in the peripheral nervous system may be myelinated. Myelin sheaths are formed by Schwann Cells. Schwann cells form multiple layers of membrane around the neuron and insulate it. In between the areas if myelin sheath, Nodes of Ranvier or bare patches exist. The nerve impulse or action potential will jump from node to node greatly increasing the speed of nerve transmission. This node to node transmission, called saltatory conduction, can produce transmission speeds of up to 200 meters per second and explains the speed at which we can react to potentially harmful stimuli.

Schwann cells - Glial cells that myelinate the axons of peripheral nerves. These cells wrap their cytoplasm in a spiral fashion around short segments of axons. Because the myelin sheath is formed from numerous Schwann cells arranged sequentially along the axon, there are gaps between adjacent myelinating cells producing myelin-free areas of axon called Nodes of Ranvier. These play an important role in nerve impulse conduction.

Myelin Myelination begins with the invagination of a single nerve axon into a Schwann cell; a mesoaxon is then formed. As myelination proceeds, the mesoaxon rotates around the axon enveloping it in concentric layers of Schwann cell cytoplasm and plasma membrane.