Activation of E leads to graded excitatory postsynaptic potentials (EPSPs), the larger of which reaches threshold (approximately −40 mV) for an action potential. The action potential is followed by an after-hyperpolarization (AHP), the magnitude and duration of which determine when the next action potential can occur.
Right trace shows membrane potential (in millivolts [mV]), beginning at a typical resting potential (−70 mV).
Activation of I causes an inhibitory postsynaptic potential (IPSP).
The inset shows a magnified portion of the neuronal membrane as a lipid bilayer with interposed voltage-gated N A + and K+ channels; the direction of ion fluxes during excitatory activation is indicated. After firing, the membrane-bound N A +-K+ pump and star-shaped astroglial cells restore ionic balance.