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How do myelinated axons help signals travel through white matter?

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Diagram comparing action potential conduction in myelinated and unmyelinated axons, showing a neuron with labeled cell body, myelin sheath, nodes of Ranvier, and the flow of electrical signals along each type of axon. — nervous system In a myelinated axon, the myelin sheath prevents the local current (small black arrows) from flowing across the membrane. This forces the current to travel down the nerve fibre to the unmyelinated nodes of Ranvier, which have a high concentration of ion channels. Upon stimulation, these ion channels propagate the action potential (large green arrows) to the next node. Thus, the action potential jumps along the fibre as it is regenerated at each node, a process called saltatory conduction. In an unmyelinated axon, the action potential is propagated along the entire membrane, fading as it diffuses back through the membrane to the original depolarized region.

In the central nervous system, white matter is primarily composed of bundles of myelinated axons that facilitate communication between different brain regions. The myelin sheath acts as a high-resistance, low-capacitance electrical insulator, preventing ions from crossing the membrane along the covered segments of the axon.123

Because the myelin prevents ion exchange, electrical signals spread passively along the axon until they reach the nodes of Ranvier—periodic, unmyelinated gaps in the sheath. These nodes are densely packed with ion channels that regenerate the action potential upon stimulation. This arrangement allows the nerve impulse to "jump" rapidly from one node to the next, a highly efficient process known as saltatory conduction. By enabling this rapid, saltatory transmission, myelinated axons ensure that signals travel quickly and effectively through the white matter tracts of the brain and spinal cord.2451