Why is the conduction velocity in a large myleinated axon very high? Isn the current lost due to the increase in surface area of the axon?
You’re right that more current is lost through the membrane of large diameter axon than from a small diameter axon but the effect of this loss is small compared to the increased current down the length of the larger cell. So even though current is lost from a large cell enough is preserved via its longer length contant to result in a higher conduction velocity. The effects are proportionately the same, but magnified for myelinated cells.