Explain how an action potential is generated in a Nerve cell?

At rest a Nerve cell has active Sodium/Potassium pumps that pump 3 Na+ ions out of the nerve cell and 2 K+ ions into the nerve Cell. This generates a concentration gradient and makes the resting potential of the nerve cell -60mV (millivolts). When a receptor is activated such as a pacinian receptor it converts the energy from the signal into electrical energy that raises the charge in the neuron to -55mV otherwise known as the threshold potential. This slight depolarisation of the nerve cell opens voltage gated Na+ ion channels that allow Na+ ions to diffuse into the nerve cell raising the potential difference to +40mV. This process is known as depolarisation of the nerve cell. At +40mV the V-G Na+ ion channels close and the V-G K+ ion channels open causing the K+ ions that were in the nerve cell previously to diffuse out of the nerve cell thus repolarising the cell and lowering the potential difference of the nerve cell to -70mV due to the loss of positive ions. The reason the potential difference is lowered to -70mV as oppose to the resting potential of -60mV is so the nerve cell can not send multiple action potentials at the same time and it gives a brief period for the nerve cell to recover before generating another action potential and this process is known as hyperpolarisation. The positive ions that generated the action potential diffuse along the axon of the neuron allowing the signal to be conducted across the body.