Myelin

Myelin Sheath is a <a href="/facts/Lipid/TdQR87HX">lipid</a>-rich material that in most <a href="/facts/Vertebrate/tT54FSTT">vertebrates</a> surrounds the <a href="/facts/Axons/5DCd4wLo">axons</a> of <a href="/facts/Neuron/G7CyTVdH">neurons</a> to <a href="/facts/Insulator_(electricity)/SfSXkrh5">insulate</a> them and increase the rate at which electrical impulses (called <a href="/facts/Action_potential/Sz8yCRqx">action potentials</a>) pass along the axon. The myelinated axon can be likened to an electrical wire (the axon) with insulating material (myelin) around it. However, unlike the plastic covering on an electrical wire, myelin does not form a single long sheath over the entire length of the axon. Myelin ensheaths part of an axon known as an <a href="/facts/Internodal_segment/8Lz9T7a0">internodal segment</a>, in multiple myelin layers of a tightly regulated internodal length. 
The ensheathed segments are separated at regular short unmyelinated intervals, called <a href="/facts/Node_of_Ranvier/K7dv9RPF">nodes of Ranvier</a>. Each node of Ranvier is around one <a href="/facts/Micrometre/7eDFxD2L">micrometre</a> long. Nodes of Ranvier enable a much faster rate of <a href="/facts/Conduction_of_electricity/akyCKvMy">conduction</a> known as <a href="/facts/Saltatory_conduction/FWBFSsbU">saltatory conduction</a> where the <a href="/facts/Action_potential/Sz8yCRqx">action potential</a> recharges at each node to jump over to the next node, and so on till it reaches the <a href="/facts/Axon_terminal/QhUJg8SH">axon terminal</a>. At the terminal the action potential provokes the release of <a href="/facts/Neurotransmitter/LlpYFSU3">neurotransmitters</a> across the <a href="/facts/Synapse/vdMRJCUn">synapse</a>, which bind to <a href="/facts/Neurotransmitter_receptor/6a6WnCwT">receptors</a> on the post-synaptic cell such as another neuron, <a href="/facts/Myocyte/cP7Jea3q">myocyte</a> or <a href="/facts/Secretory_cell/VHk9eLAV">secretory cell</a>.
Myelin is made by specialized non-neuronal <a href="/facts/Glial_cells/F8BhPmaA">glial cells</a>, that provide insulation, and <a href="/facts/Nutrition/SMJ3Dhfs">nutritional</a> and <a href="/facts/Homeostatic/rloTGAHa">homeostatic</a> support, along the length of the axon. In the <a href="/facts/Central_nervous_system/k8I6To97">central nervous system</a>, myelination is formed by glial cells called <a href="/facts/Oligodendrocyte/vjyKr3w2">oligodendrocytes</a>, each of which sends out <a href="/facts/Cellular_extensions/7Q88oJJg">cellular extensions</a> known as <a href="/facts/Foot_processes/QnFbjc96">foot processes</a> to myelinate multiple nearby axons. In the <a href="/facts/Peripheral_nervous_system/KjVpVnHU">peripheral nervous system</a>, myelin is formed by <a href="/facts/Schwann_cell/fcdM1444">Schwann cells</a>, which myelinate only a section of an axon. In the CNS, axons carry electrical signals from one nerve cell body to another. 
The "insulating" function for myelin is essential for efficient <a href="/facts/Motor_function/IwK2rqNW">motor function</a> (i.e. movement such as walking), <a href="/facts/Sense/cB7rTqYF">sensory function</a> (e.g. <a href="/facts/Sight/g7Tfaq2l">sight</a>, <a href="/facts/Hearing/EPYrVkSx">hearing</a>, <a href="/facts/Olfaction/t6ytFklU">smell</a>, the feeling of <a href="/facts/Touch/0nhRsBnt">touch</a> or <a href="/facts/Pain/70E79oUn">pain</a>) and <a href="/facts/Cognition/ga0tSBul">cognition</a> (e.g. acquiring and recalling knowledge), as demonstrated by the consequence of disorders that affect myelination, such as the genetically determined <a href="/facts/Leukodystrophies/1KA87hfs">leukodystrophies</a>; the acquired inflammatory <a href="/facts/Demyelinating_disease/NAaGAHPV">demyelinating disease</a>, <a href="/facts/Multiple_sclerosis/vghXl0IQ">multiple sclerosis</a>; and the inflammatory demyelinating <a href="/facts/Peripheral_neuropathies/2KjA7nyD">peripheral neuropathies</a>. Due to its high prevalence, multiple sclerosis, which specifically affects the central nervous system, is the best known demyelinating disorder.

Myelin open-in-new

Myelin