March 1 The Action Potential

B. The Action Potential- When the Neuron "fires".
    1. A stimulus (motor or sensory) will cause the gated Na+ Channels to open more (unknown mechanism) at the 1st Node of Renvier at the Axon Hillock.
     2.This causes the resting charge to raise (become less negative)
     3.If, enough Na+ enters to get the charge to -50 Mv ( the Threshold) the Na+ channels open wide and Na+ comes rushing in causing the internal charge to move to +35 Mv (firing charge)
     4. Cl- will be left behind by the Na+ and for 1/2 of 1 ms the external environment is negative. This is the electricity.
    5. Most of the Na+ will travel laterally. The Na+ that travels into the cell body, has no effect, but the Na+ that travels to the next node will cause that to reach the threshold, and it will fire there.
    6. The Na+, again, will travel laterally. As it moves to the previous node, no effect will occur because the potential for firing has not been reset by the Na+/K+ pumps (it takes 3 ms to reset) this is why the impulse is 1-directional. But, when it travels to the node that is set to fire the same thing will happen there and this continues down the line to the end of the neuron.
All or Nothing Rule- When a neuron fires it will always fire at 100% intensity.