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A constructive plate margin can also be called a divergent plate margin, and it is where two tectonic plates move in opposite directions away from one another. Magma rises up between the plates forming new crust (hence constructive plate margin).
Volcanos are common here due to the rising magma, and earthquakes can occur but they are generally minor.see more
At rest, the potential difference between the inside and outside of the neuron is around -70mV. The sodium potassium pump is continually pumping 3 Na+ ions out for every 2 K+ ions it pumps in, and this maintains the resting potential of -70mV.
During an action potential a few sodium ion channels open, and Na+ diffuses into the neuron, decreasing the value of the potential difference. If and when the potential difference reaches the threshold potential of -50mV voltage-gated sodium ion channels open and the neurone is depolarised reaching a maximum potential difference of +40mV.
At this point the sodium ion channels close and potassium ion channels open allowing K+ ions to diffuse out of the neuron which is repolarised to -70mV. Generally this target is overshot (hyperpolarisation) to about -90mV, but the sodium-potassium pump corrects this.see more