Explain how a nerve impulse passes along a non-myelinated neuron.
Because the sodium-potassium pump moves three sodium out for every two ions, there is a higher concentration of sodium on the outside and a higher concentration of potassium on the inside. This, together with negatively charged proteins and chloride ions inside the cell, creates a negative charge on the inside, and a positive charge on the outside. When a rapid change in the membrane potential surpasses the threshold, caused by a stimulus strong enough to trigger depolarization, voltage-gated sodium ion channels open, followed quickly by the opening of the potassium channels. When the gates open, sodium and potassium go down their concentration gradients. The sodium gates open first, creating the rising phase. Then the pottasium gates open, which leads to the falling phase, culminating in an undershoot. This has to be resolved by the sodium-pottasium pump in order to restore the resting potential (repolarizing)