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Glia - Schwann cell only wraps one segment of an axon Thus...

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Glia Glia are a diverse class of cells that perform many functions within the nervous system. Two types of glia cells make the special lipid structure known as myelin . The cells that produce myelin wrap their plasma membranes around the axons which forms an insulating layer around these axons. Myelin sheaths greatly speed up the rate of conduction of an action potential. As myelin prevents the movement of ions across the cell membrane (recall that APs are the result of the movement of Na and K ions), to enable action potentials to propagate, there are regular gaps between myelin segments called nodes of Ranvier. An AP jumps from node to node as it moves down the axon. The initial segment of the axon and the axon hillock form the trigger zone where signals begin. In the CNS, oligodendrocytes form the myelin sheaths and one oligodendrocyte can wrap around many neuronal axons. Schwann cells myelinate the axons of the PNS and a
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Unformatted text preview: Schwann cell only wraps one segment of an axon. Thus, each PNS axon has several Schwann cells surrounding it. Astrocytes have foot processes that cover the capillaries of the brain. These foot processes help regulate what is able to diffuse out of the blood and into the CNS. Astrocytes are essential in forming the blood-brain barrier , which protects the CNS from blood-borne proteins, toxins, and cells. Ependymal cells line the cavities of the brain and produce cerebrospinal fluid . Microglia help remove pathogens and debris and are actually specialized phagocytotic white blood cells. These are usually concentrated in areas of infection, trauma or stroke. A last type of glia are satellite cells. The function of these cell is still under investigation....
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