The Schwann cells , Also known as neurolemocitos, constitute a specific type of glial cells of the nervous system of the brain .
These cells are located in the peripheral nervous system And its main function is to accompany the neurons during their growth and development.
Schwann cells are characterized by covering the extensions of the Neurons . That is, they are located around the axons forming an insulating sheath of myelin in the outer layer of neurons.
Schwann cells present their analogues within the Central Nervous System , Oligodendrocytes. That is, while the Schwann cells form part of the peripheral nervous system And are located on the outside of the axons, the ligodendrocytes belong to the nervous system center and cover the axons with their cytoplasm .
At present, many conditions have been described that can alter the functioning of this type of cells, the most multiple sclerosis .
This article explains the main characteristics of this peculiar type of cells. Its anatomical properties and functions are reviewed and the pathologies associated with Schwann cells are discussed.
Characteristics of Schwann cells
Schwann cells are a type of cell that was first described in 1938 by Theodor Schwann .
These cells constitute the glia of the peripheral nervous system and are characterized by surrounding axons of the nerve. In some cases, this action is carried out by wrapping the axons through their own cytoplasm, and in other cases it develops through the elaboration of a myelin sheath.
Schwann cells perform multiple functions within the peripheral nervous system and are highly important substances for achieving optimal brain function.
Its main function lies in the protection and axonal metabolic support. They also contribute to nerve conduction processes.
The development of Schwann cells, as is the case with most cells in the peripheral nervous system, derives from a transient embryonic neural crest structure.
However, it is unknown at what embryonic stage neural crest cells begin to differentiate and constitute what are known as Schwann cells.
Structure
The main property of Schwann cells is that they contain myelin (a multilaminar structure that is formed by the plasma membranes surrounding the axons).
Depending on the diameter of the axon in which the Schwann cells are attached, they can develop distinct functions and activities.
For example, when this type of cells accompany small (narrow) nerve axons, a layer of myelin develops that can be housed in different axons.
In contrast, when Schwann cells cover larger diameter axons, there are circular bands without myelin known as Ranvier nodes. In this case, the myelin is composed of concentric layers of membrane cells that spiral around the axon of the difference.
Finally, it should be noted that the Schwann cells can be found in the axonal terminals and the synaptic buttons of the neuromuscular junctions, where they provide a physiological support for the maintenance of the ionic homeostasis of the synapse.
Proliferation
The proliferation of Schwann cells during the development of the peripheral nervous system is intense. Certain studies suggest that such proliferation is dependent on a mitogenic signal provided by the growing axon.
In this sense, the proliferation of these substances of the peripheral nervous system takes place in three main contexts.
- During the normal development of the peripheral nervous system.
- After a nerve injury due to mechanical trauma by neuro-toxins or demyelinating diseases.
- In cases of Schwann cell tumors such as those observed in the case of neurofibromatosis and acoustic fibromas.
Development
The development of Schwann cells is characterized by an embryonic phase and a neonatal rapid proliferation and its final differentiation. This developmental process is very common among peripheral nervous system cells.
In this sense, the normal development of Schwann cells presents two main stages: the migratory stage and the myelinizing stage.
During the migratory phase, these cells are characterized by being long, bipolar and with a composition rich in micro-filaments, but with absence of myelin basal lamina.
Subsequently, the cells continue to proliferate and the number of axons per cell decreases.
Simultaneously, larger diameter axons begin to segregate from their similar ones. At this stage, the spaces of connective tissue in the nerve have already developed better and the basal laminae of myelin begin to be observed.
Functions
Schwann cells act in the peripheral nervous system as electrical insulators through the myelin. This insulation is responsible for wrapping the axon and cause an electrical signal that runs without losing the intensity.
In this sense, Schwann cells give rise to so-called saltatory conduction of myelin-containing neurons.
On the other hand, these types of cells also help to guide the growth of axons and are basic elements in the regeneration of certain lesions. Especially, they are vital substances in the regeneration of brain damage originating in neuropraxia and axonotmesis.
Related diseases
The vitality and functionality of Schwann cells can be affected through multiple factors of diverse origin. In fact, infectious, immune, traumatic, toxic or tumor problems can affect the activity of this type of cells of the peripheral nervous system.
Among the infectious factors, Mycobacterium leprae and the Corynebacterium diphtheriae , Microorganisms that cause alterations in Schwann cells.
Among the metabolic disorders, diabetic neuropathy . The tumor pathologies that affect this type of cells are
- During the normal development of the peripheral system.
- After a nerve injury due to mechanical trauma by neuro-toxins or demyelinating diseases.
- Plexiform fibroids.
- Malignant fibroids.
Finally, the loss or demyelination of the neuron can generate pathologies that affect the central nervous system, as it happens with multiple sclerosis.
References
- Bunge MB, WilliarnsAK, WoodPM.NeuronSchwann et al. Interaction in basal lamina formation. Dev. Biol. 1982; 92: 449.
- Gould RM. Metabolic Organization of the Neoinating Schwann Cells. Ann. N.Y. Acad. Sci. 1990; 605: 44.
- Jessen KR, and Mirsky R. Schwann cell precursors and their deveioprnent. Glia. 1991, 4: 185.
- Birdi T Jand Anthia NH. Effect of M. erprae infected Schwann ceils and their supernatant on lymphocyte neuroglia interaction. JNeuroimmunol. 1989,22: 149-155.