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Con­duc­tion along a Nerve Fiber

Okay so we just talked about con­duc­tion in an unnerve fiber.  What about a one?  In nerve fibers, the depo­lar­ized Node of Ran­vier trig­gers an increase in the per­me­abil­ity of the sodium ion chan­nels (and thus depo­lar­iza­tion) in the adja­cent Node of Ran­vier.

Above we see a .  If the cells are wrapped around central nerves, they are oligo­dendrocytes. If they’re wrapped around   the  peripharal nerves they’re called Schwaan cells. In either case there are these gaps called Nodes of Ranvier.  The only place these potassium or sodium ions can enter or leave are from these spaces that are unmyeli­nated.  Sodiums come in and potassiums going out just like a an unmymelinated nerve fiber, except this signal seems to jump from one node to the next. This is called saltatory conduction. It has noth­ing to do with salt but it comes from the latin word saltaire which means to jump or leap.

Due to this skip­ping, saltaory conduction is up to 50 times faster than con­duc­tion through the fastest unaxons because they don’t have to travel through­out every sin­gle space before mov­ing to the next.

So in essence, the action poten­tial is gen­er­ated only at the nodes.  The cell mem­brane below the myelin sheaths hardly have any sodium chan­nels and are there­fore not excitable anyway.  Since the ionic cur­rents are restricted to the nodes of Ranvier in the axons, this minimizes disturbances in the Na⁺/K⁺ concentration gradients which reduces the energy costs of the Na+/K+-ATP pump that have to restore ionic balance.

Continue to Saltuatory conduction Video