Dat is niet wat ik bedoelde. Ik weet wel hoe het actiepotentiaal en het rustpotentiaal werkt. Maar ik dacht dat energie in één richting wordt geleidt: zowel via de axoplasm als ook via de extracellulaire vloeistof (buitenste peilen). In het plaatje scheppen de tegen overstaande peilen verwarring bij mij. Hier is het volledige stukje tekst uit Guyton & Hall (2011):
"Saltatory" Conduction in Myelinated Fibers from Node to Node
Even though almost no ions can flow through the thick myelin sheaths of myelinated nerves, they can flow with ease through the nodes of Ranvier. Therefore, action potentials occur only at the nodes. Yet the action potentials are conducted from node to node, as shown in Figure 5-17; this is called saltatory conduction. That is, electrical current flows through the surrounding extracellular fluid outside the myelin sheath, as well as through the axoplasm inside the axon from node to node, exciting successive nodes one after another. Thus, the nerve impulse jumps along the fiber, which is the origin of the term "saltatory."
Saltatory conduction is of value for two reasons. First, by causing the depolarization process to jump long intervals along the axis of the nerve fiber, this mechanism increases the velocity of nerve transmission in myelinated fibers as much as 5- to 50-fold. Second, saltatory conduction conserves energy for the axon because only the nodes depolarize, allowing perhaps 100 times less loss of ions than would otherwise be necessary, and therefore requiring little metabolism for re-establishing the sodium and potassium concentration differences across the membrane after a series of nerve impulses.
Still another feature of saltatory conduction in large myelinated fibers is the following: The excellent insulation afforded by the myelin membrane and the 50-fold decrease in membrane capacitance allow repolarization to occur with little transfer of ions.
Veranderd door Pizza Monster, 17 maart 2012 - 16:29