Dorothy FarrarSchwann cells
The glial cells of the peripheral nervous system are called Schwann cells . They form the myelin of peripheral axons and thus electrically insulate the neurons from their surroundings. Together with the Ranvier stoking rings, the Schwann cells ensure the conductivity of the nerve tissue.
Definition
The Schwann cells are a form of glial cells. There are about ten types of glial cells in the nervous system. They can be up to 100 µm long and electrically insulate the internode between the cords of nerve fibers from the environment. The Schwann cells are found as insulation in the peripheral nervous system.
They do not exist in the central nervous system. Here the so-called oligodendrocytes take over the functions of the Schwann cells. Although all glial cells were long thought to have only supporting and isolating functions, they are now also known as nurturers and organizers of the nervous system.
The anatomist Theodor Schwann is the namesake of the Schwann cells. He first described them in the 19th century.
Anatomy
Schwann cells contain large amounts of cytoplasm in the outer region and a nucleus of their own . This section of cells is also called Schwann’sches Scheid or neurolemm. The so-called basal lamina is arranged around the neurolemma. It is a homogeneous layer of proteins that forms the basis of the epithelial cells and connects the neurolemma to the surrounding connective tissue of the nearest nerve fibers.
As glial cells, these Schwann cells form the myelin of the peripheral nervous system and thus envelop the nerve fibers containing the myelin. For this purpose, in the organism of vertebrates, the Schwann cells wrap themselves several times around the internodal sections of the axons and thus electrically insulate them from the environment. However, the nerve fibers are not continuously insulated.
The Schwann cell mantle has regular discontinuities called Ranvier cinder rings. These rings generate action potentials and optimize nervous system conduction velocity by establishing saltatory conduction.
The stoking rings are located in the peripheral nervous system at a distance of 0.2 to 1.5 millimeters from each other. Diagonal interruptions in the myelin are also called Schmidt-Lantermann notches.
Function
The Schwann cells mainly fulfill supporting functions and stabilize the framework of peripheral nerves. However, they are also responsible for nourishing the nerve fibers and, as the myelin sheath, also take on the role of an insulating layer. They play ideally together with the Ranvier stoking rings and together with them enable the saltatoric transmission of excitation, as it takes place in nerve tissue.
The action potential arises in the unmarked Schürringen. Meanwhile, the Schwann cells surround the axons of myelinated nerves. They insulate them electrically and thus give the nerves their electrical conductivity. The insulating jacket can almost be compared to the plastic of a plastic cable. The myelin corresponds to a fatty protein substance and, like the plastic of the cable, prevents electrical excitation from migrating from the axons to the periphery.
Without the myelin, the action potentials of the nervous system would simply get lost in the environment. In extreme cases, excitation transmission would no longer be possible at all. The Schwann cells also protect the nerve lines from foreign stimuli by insulating them, thereby increasing the capacity and effectiveness of the axons.
In this way, they ensure the smooth and rapid excitation process, which is essential for reflexes, perception, motor activity and vegetative bodily functions. The myelinated fibers of the nervous system work much faster than the unmyelinated axons, which supply cytoplasm to the Schwann cells.
Diseases
- Miller-Fisher-Syndrom
Demyelinating diseases attack the myelin, reducing nerve excitability and conductivity. In the peripheral nervous system, such a demyelination always corresponds to a destruction of the Schwann cells.
Miller-Fisher syndrome is a demyelinating disease that causes inflammation in peripheral nerve tissue, destroying the myelin sheath around neurons. Motor reflexes can no longer be triggered with this disease. Peripheral paralysis and movement insecurity are among the main symptoms.
A demyelinating disease with similar key symptoms is funicular myelosis. Not only inflammation, but also toxic reactions can attack the Schwann cells. Equally often, demyelination is preceded by malnutrition . Infectious causes are also possible causes of peripheral demyelination. Diseases such as leprosy in particular can have a corresponding effect.
However, cancer and diabetes also sometimes attack the Schwann cells. In the peripheral nervous system, demyelination is basically understood as a polyneuropathy, which is sometimes also caused by an injury to the nerve fibers. After demyelination, there are sensory disturbances and neurological deficits.
Damaged Schwann cells can regenerate. Unlike the glia of the peripheral nervous system, the central nervous system glia usually cannot fully recover from demyelination because of their high degree of specialization.
Hello and welcome to my Health Guide & Encyclopedia! My name is Dorothy Farrar, and I'm the founder and main author of this platform.
My passion for health and wellness started at a young age when I became interested in the connection between the food we eat and the way we feel. This fascination led me to study nutrition and dietetics in college, where I learned about the importance of a balanced diet and the impact of various nutrients on the body.