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Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory ensheathing cells, enteric glia and glia that reside at sensory nerve endings, such as the Pacinian corpuscle.
Neurilemma (also known as neurolemma, sheath of Schwann, or Schwann's sheath) [1] is the outermost nucleated cytoplasmic layer of Schwann cells (also called neurilemmocytes) that surrounds the axon of the neuron. It forms the outermost layer of the nerve fiber in the peripheral nervous system. [2]
The nonmyelinating Schwann cells are a subgroup of the Schwann cells characterized by not forming myelin. [1]The group of nonmyelinating Schwann cells includes the terminal Schwann cells, present at neuromuscular junctions, the Schwann cells of Remak fibers (also called Remak Schwann cells) and the Schwann cells associated to sensory structures, like tactile corpuscles and lamellar corpuscles.
Schwann dedicated a chapter of the treatise to explicitly formulate the cell theory, stating that ("the elementary parts of all tissues are formed of cells” and that “there is one universal principle of development for the elementary parts of organisms... and this principle is in the formation of cells" (Henry Smith's translation, 1847).
The nucleus is the source of most of the RNA that is produced in neurons. In general, most proteins are produced from mRNAs that do not travel far from the cell nucleus. This creates a challenge for supplying new proteins to axon endings that can be a meter or more away from the soma.
Schwann claimed that "there is one universal principle of development for the elementary parts of organisms, however different, and this principle is the formation of cells." [34] Schwann supported this claim by examining adult animal tissues and showing that all tissues could be classified in terms of five types of highly differentiated ...
Schwann cells continue to clear up the myelin debris by degrading their own myelin, phagocytose extracellular myelin and attract macrophages to myelin debris for further phagocytosis. [11] However, the macrophages are not attracted to the region for the first few days; hence the Schwann cells take the major role in myelin cleaning until then.
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