Schwann cell

In the Schwann cell ( Gliocytus periphericus, also Schwann cell or Lemnozyt ) is a special type of glial cell. It forms a sheath and supporting cell that surrounds the axon of a nerve cell in the peripheral course and in myelinated fibers electrically insulated by a myelin sheath.

History

Your name has it by its discoverer, the German anatomist and physiologist Theodor Schwann ( 1810-1882 ).

Design and function

Schwann cells there are only in the peripheral nervous system. They serve the formation of myelin sheaths, which cause an insulation of the axons, so that their conduction velocity is increased. In the central nervous system, the same function is fulfilled by oligodendrocytes.

Schwann cells attach themselves to the axons of nerve fibers. Initially, remains undetermined at how many nerve fibers and to what extent they do so. Are they only half or simply attached to the axons, is still spoken of unmyelinated nerve fibers. Only the resulting Mehrfachumwickelung by a fat-protein mixture is referred to as myelin or the nerve fiber as medullated. It should be noted that the Schwann cells are not able, in contrast to the oligodendrocytes to completely encase several axons; should an addition taking place at several axons, so this will never lead to a complete wrap. Another difference is that Schwann cells after injury axonal regeneration, the axon regrowth cause - a capability which does not have the oligodendrocytes, and therefore the regeneration of the CNS in mammals is limited.

About one third of all the nerve fibers, the Schwann cell growth during wound several times around an axon. The Schwann cell can often wrap around an axon only in vertebrates.

In the outer region of a Schwann cell is not wraps around the axons and is not involved in the myelin are the cytoplasm and the nucleus. This part is also called Schwann sheath or neurilemma. It is surrounded by a basal lamina, which connects it to the surrounding connective tissue endoneurium. When an axon regrowth after injury, the persistence of the basal lamina is significant because it sets the axon of the way.

Between adjacent Schwann cells along the axon it comes to regular interruptions of the myelin sheath. These are called nodes of Ranvier. Here, the important for the increase of nerve conduction velocity saltatory conduction.

Because vertebrates have Schwann cells, but other species, such as arthropods, not, this is for large vertebrates due to the significantly higher reaction rate an evolutionary advantage. For smaller animals, this advantage disappears because there assume the chemical transmission of information in the synapses of the most time consuming.

Diseases

Among the acquired inflammatory diseases, which run with the involvement of Schwann cells, including chronic inflammatory demyelinating neuropathy ( CIDP ), Guillain- Barré syndrome (GBS ) and leprosy. Among the hereditary diseases with Schwann cell involvement include the Charcot -Marie -Tooth, the Krabbe's disease and Niemann -Pick disease. Benign tumors of Schwann cells called schwannoma or neurinoma. Multiple sclerosis ( MS) as a result of autoimmune, inflammatory initiated destruction of the myelin sheath can be also mentioned here. The efforts of medical research aimed towards repair and interrupting the chain formation. There are extensive statistics on row medication inter alia with cortisone doses followed by observation vector.