1. Initiation or Generation of a Nerve Impulse (Action Potential)
 At rest, the voltage-sensitive sodium and potassium gates in the channels in the plasma
membrane of a nerve cell are nearly closed and the Na+/K+ pump moves 3 Na+ ions to the ECF
and 2 K+ ions to the ICF.
 This contributes to the formation of a resting membrane potential of -70 millivolts (mV).
 Resting Membrane Voltage (RMV)
Initiation of the Nerve Impulse Continued:
 The sodium/potassium pump also contributes to the resting membrane potential by pumping
out three sodium ions to the ECF and pumping in two potassium ions to the ICF.
 The effect of this process is to make the outside of the nerve cell positive compared to the
inside of the cell which becomes negative (-70 mV).

2.  At rest, the ICF of an axon has a voltage of about -70 mV
 When the membrane of the axon is properly stimulated, Na+ ions begin to leak into the ICF. This
causes the voltage to change to a less negative state.
 When ICF voltage reaches a threshold of about - 55 mV, sodium gates open.
 As sodium gates open, Na+ flow through sodium channels increases and quickly changes the
voltage from a resting level of - 70 mV to + 30mV.
 This rapid shift from a negative to a positive state is called DEPOLARIZATION.
 At +30 mV, the sodium gates close.
 When the sodium gates close at +30 mV, the depolarization process stops.
 Interestingly, the + 30 mV condition causes the potassium gates to open and allows potassium
to flow from the ICF to the ECF.
 The potassium flow quickly reverses the potential from + 30 mV to about - 70mV. This is called
REPOLARIZATION.
 The rapid depolarization and repolarization process generates a a voltage pulse peak that is
called the ACTION POTENTIAL or NERVE IMPULSE.
 The formation of a nerve impulse stimulates the formation of still another nerve impulse in the
next section of the axon membrane

4. Overview of Transmission of Nerve Impulse
 Action potential
→ synaptic knob
→ opening of Ca+ channels
→ neurotransmitter vesicles fuse with membrane
→ release of neurotransmitter into synaptic cleft
→ binding of neurotransmitter to protein receptor molecules on receiving neuron
membrane
→ opening of ion channels
→ triggering of new action potential
 Neurotransmitter is broken down by enzymes & ion channels close -- effect brief and precise
 How a synapse works