These slow-conducting axons are arranged in a structure which is bundle-like. In addition to insulating axons, Schwann cells are vital in response to axon damage within the PNS as they can help in regenerating the axons. Any injury to the axon can result in the death of cells and axonal degeneration.
When any type of injury occurs, the Schwann cells are sent to the injury site in order to remove dead cells. The Schwann cells have the capacity to occupy the original space of the neurons and regenerate the fibres in such a way that they are able to return to their original target sites. The Schwann cells undergo many changes during axonal regeneration. They active myelin breakdown and up-regulate the expression of cytokines a large group of proteins secreted by the immune system.
This up-regulation helps to recruit macrophages, which are specialised cells that function to detect and destroy harmful organisms. The macrophages are sent to the site of the injury to clean up the damage. The Schwann cells increase the amount of growth factors, such as neurotrophins, which are proteins that increase the survival and function of neurons.
They also secrete proteins such as laminin and collagen and cell adhesion molecules involved in binding with other cells to support the regeneration process. The stump of a damaged axon can sprout, allowing them to grow. The Schwann cells arrange a regeneration pathway along a tube of the basal lamina.
The sprout of the damaged axon can then grow through this tube which helps to stimulate and guide its regeneration. Due to this, the regenerated axons can reconnect with muscles and organs that they previously controlled with the help of the Schwann cells.
Schwann cells are therefore especially important as regenerated axons will not reach their target areas without their support. Schwann cell dysfunction is primarily associated with demyelinating diseases of the PNS.
Demyelination in the PNS describes a pathologic process of destruction of myelin-supporting cells, therefore destroying normal myelin. These dysfunctions could be as a result of genetic mutations, autoimmune responses, infections, and trauma. These causes can impair the myelination process and the functions of the Schwann cells and axons, eventually leading to neurodegeneration.
The insulating myelin segments could be lost or destroyed, and conduction of neuronal electrical impulses down the axon can be diminished or blocked. Demyelinating diseases can range from acute to chronic and some symptoms of these diseases can be characterised as weakened reflexes, weakness, sensory loss, slower nerve conduction, and paralysis. Disorders which cause damage to the myelin sheath of the PNS, ultimately affecting the function of Schwann cells and axons, are called peripheral demyelinating diseases.
With this disorder, the immune system attacks healthy nerve cells in the PNS, resulting in symptoms of weakness, numbness, and may eventually cause paralysis, making it a life-threatening condition if this disease affects the muscles involved with respiration. Guillain-Barre Syndrome causes damage to the axons of neurons, leading to a blockage of electrical conduction.
Although this condition damages the axons, the Schwann cells are also damage as a result, producing something called secondary demyelination. Guillain-Barre Syndrome can be treated through intravenous immunoglobulin which is a treatment comprised of blood donation that contain healthy antibodies, in order to prevent harmful antibodies damaging the axons of neurons.
Charcot-Marie-Tooth disease CMT is another peripheral demyelinating disorder that is rare and hereditary. Both sensory and motor neurons can be affected by this disease, disrupting overall Schwann cell structure and function. This can affect a lack of growth in Schwann cells as well as abnormal amounts of Schwann cells between the nodes of Ranvier gaps in the myelin sheath that function to increase conduction of impulses.
Symptoms of CMT can include having weak muscles, loss of sensation in the feet and legs, difficulty walking, and deformities in the feet such as having a high arch and bent toes. Connexin29 is uniquely distributed within myelinating glial cells of the central and peripheral nervous systems.
Beirowski, B. Metabolic regulator LKB1 is crucial for Schwann cell-mediated axon maintenance. Bienfait, H. Late onset axonal Charcot-Marie-Tooth phenotype caused by a novel myelin protein zero mutation. Psychiatry 77, — Brennan, K. Brown, A. Schwann cell glycogen selectively supports myelinated axon function.
Bullock, T. Evolution of myelin sheaths: both lamprey and hagfish lack myelin. Camargo, N. Oligodendroglial myelination requires astrocyte-derived lipids. PLoS Biol. Campana, W. Ionotropic glutamate receptors activate cell signaling in response to glutamate in Schwann cells. Chakraborty, G. Intraneuronal N-acetylaspartate supplies acetyl groups for myelin lipid synthesis: evidence for myelin-associated aspartoacylase. Chamberlain, K. Mechanisms for the maintenance and regulation of axonal energy supply.
Chen, X. Oxidative stress in neurodegenerative diseases. Neural Regen. Cooper, M. A ketogenic diet reduces metabolic syndrome-induced allodynia and promotes peripheral nerve growth in mice. Reduced mitochondrial reactive oxygen species production in peripheral nerves of mice fed a ketogenic diet. Distribution of monocarboxylate transporters in the peripheral nervous system suggests putative roles in lactate shuttling and myelination. Ebenezer, G. Denervation of skin in neuropathies: the sequence of axonal and Schwann cell changes in skin biopsies.
Brain , — Feldman, E. New horizons in diabetic neuropathy: mechanisms, bioenergetics, and pain. Neuron 93, — Fledrich, R. Targeting myelin lipid metabolism as a potential therapeutic strategy in a model of CMT1A neuropathy. Axo-glial interdependence in peripheral nerve development. Development dev Glycolytic oligodendrocytes maintain myelin and long-term axonal integrity.
Nature , — Griffiths, I. Axonal swellings and degeneration in mice lacking the major proteolipid of myelin. Science , — Jha, M. Monocarboxylate transporter 1 in Schwann cells contributes to maintenance of sensory nerve myelination during aging. Glia 68, — Klugmann, M. Assembly of CNS myelin in the absence of proteolipid protein. Neuron 18, 59— Lemus, H. Multiple sclerosis: mechanisms of disease and strategies for myelin and axonal repair. Liu, L. Cell Metab. Magnani, P.
Metabolism 45, — Malik, R. Sural nerve pathology in diabetic patients with minimal but progressive neuropathy. Diabetologia 48, — Michailov, G. Axonal neuregulin-1 regulates myelin sheath thickness. Misu, K. An axonal form of Charcot-Marie-Tooth disease showing distinctive features in association with mutations in the peripheral myelin protein zero gene ThrMet or Asp75Val. Psychiatry 69, — Morrison, B. Deficiency in monocarboxylate transporter 1 MCT1 in mice delays regeneration of peripheral nerves following sciatic nerve crush.
Nave, K. Myelination and the trophic support of long axons. Glial cell evolution: the origins of a lipid store. Prukop, T. PLoS One e Rich, L. Fibre sub-type specific conduction reveals metabolic function in mouse sciatic nerve.
Rodrigues, F. Comparing peripheral glial cell differentiation in Drosophila and vertebrates. Life Sci.
Overview of neuron structure. Overview of neuron function. Schwann cells. Next lesson. Current timeTotal duration Google Classroom Facebook Twitter. Video transcript In this video, I want to talk about Schwann cells. Schwann cells are glia of the peripheral nervous system derived from neural crest cells and named after a person who described them.
Schwann cells come in a couple of shapes. Some are fairly shapeless cells that have little troughs on their surface. And the axons of neurons that have small diameter axons often just sit inside these troughs. So these are neurons with a soma. And I'm leaving off the dendrites.
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