A nervous-system cell with specialised support, insulation or regulatory functions distinct from the principal signalling role of neurons.
A tanycyte is a specialized ependymal cell and glial cell of the hypothalamus. Its body can line the third ventricle, while a long process extends toward underlying tissue. In the median eminence, tanycytic endings surround neurosecretory terminals near blood vessels.[ref]
Vascular endothelial cells promote acute plasticity in ependymoglial cells of the neuroendocrine brain by Sandrine De Seranno and others. Introduction and Figure 1; ventricular cell bodies, long processes and vascular end-feet
In cultured rat tanycytes, signals from endothelial cells altered actin organization through nitric oxide.[ref]
This supplies an illuminating example of structural regulation: a glial cell can change the geometry around a neuron's ending without changing the ending's identity. Evidence for one such interaction does not establish identical functions for every tanycyte subtype.
A Schwann cell is a glial cell of the peripheral nervous system that ensheaths axons. A myelinating Schwann cell wraps its cell membrane repeatedly around one segment of one axon, producing myelin. Adjacent Schwann cells leave a node of Ranvier between their sheaths, supporting saltatory conduction.[ref]
Anatomy and Physiology 2e by J. Gordon Betts and others. Section 12.2, Glial Cells of the PNS and Myelin
Other Schwann cells support small axons without building thick myelin sheaths. Thus being associated with a Schwann cell does not imply that a peripheral fibre is myelinated. The one-segment arrangement also differs from an oligodendrocyte, whose processes can myelinate parts of several central axons.
An oligodendrocyte is a glial cell that forms myelin around axons in the central nervous system. Different processes from one oligodendrocyte can wrap separate segments of several axons. The insulated segments alternate with nodes of Ranvier, allowing saltatory conduction.[ref]
Anatomy and Physiology 2e by J. Gordon Betts and others. Section 12.2, Glial Cells of the CNS and Myelin
This branching arrangement differs from the one myelinated segment made by a peripheral Schwann cell. Insulation is part of circuit function: changes to the number or geometry of sheaths can alter when signals arrive. Experiments manipulating visual experience in mice linked altered oligodendrocyte-generated sheath geometry to changes in optic nerve conduction.[ref]
Microglia are resident immune-lineage cells of the central nervous system. They monitor and respond to tissue conditions and interact with neural connections. Their roles differ from those of neurons and from treating every glial cell as one passive supporting population.
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