Question

How nerve cells conduct impulses without myelin sheath ?

Answer 1

The membrane of nerve cells behave similar to a wire. The myelin acts as insulation. The better insulated the wire, the better it carries a charge. In the case of neurons, un-myelinated neurons conduct APs just fine, but much slower than myelinated neurons. Remember that despite the fact that an AP will degrade with distance, the AP is created by changing ion concentrations (mostly Na and K) inside vs. outside the cell. As the AP travels along the neuron, voltage-gated ion channels perpetuate the signal to keep it from degrading.