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Myelin (/ ˈ m aɪ. ə l ɪ n / MY-ə-lin) is a lipid-rich material that surrounds nerve cell axons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. [1] [2] The myelinated axon can be likened to an electrical wire (the axon) with insulating material (myelin) around it. However ...
Cell bodies of neurons are in yellow (Their axons are surrounded by myelin, produced by oligodendrocytes). Cellular extensions also known as cytoplasmic protrusions and cytoplasmic processes are those structures that project from different cells , in the body, or in other organisms.
There are two types of myelin. The first is oligodendrocyte, which can be found in the mammalian Central Nervous System (CNS). The second is Schwann cells, which are found in the Peripheral Nervous System (PNS). Myelination of axons by these Schwann cells are essential for normal nerve function.
There are two types of axons in the nervous system: myelinated and unmyelinated axons. [5] Myelin is a layer of a fatty insulating substance, which is formed by two types of glial cells: Schwann cells and oligodendrocytes. In the peripheral nervous system Schwann cells form the myelin sheath of a myelinated axon. Oligodendrocytes form the ...
Since some axons are on the order of meters long, neurons cannot rely on diffusion to carry products of the nucleus and organelles to the ends of their axons. Axonal transport is also responsible for moving molecules destined for degradation from the axon back to the cell body, where they are broken down by lysosomes. [2]
A single oligodendrocyte can extend its processes to cover up to 40 axons, that can include multiple adjacent axons. [2] The myelin sheath is not continuous but is segmented along the axon's length at gaps known as the nodes of Ranvier. In the peripheral nervous system the myelination of axons is carried out by Schwann cells. [1]
The myelin sheath that surrounds and protects nerve cells is made by cells called oligodendrocytes. In a person with MS, these cells are lost, so damaged myelin sheaths cannot be repaired.
Since an axon can be unmyelinated or myelinated, the action potential has two methods to travel down the axon. These methods are referred to as continuous conduction for unmyelinated axons, and saltatory conduction for myelinated axons. Saltatory conduction is defined as an action potential moving in discrete jumps down a myelinated axon.