Home > Conscious > Chapter 3 > 3.4. EPSP and IPSP


The opening of AMPA receptor, NMDA receptor or nAChR causes sodium and/or calcium ions to flow inward, resulting in postsynaptic membrane depolarization, thereby increasing neuronal excitability. Such potential change is called "excitatory postsynaptic potential" (EPSP). In contrast, the opening of GABAA receptor causes chloride ions to flow inward, reducing the postsynaptic membrane potential and inhibiting neuronal firing. This potential change is called "inhibitory postsynaptic potential" (IPSP).


Figure 3-7. Examples of EPSP and IPSP. [Source: Callister and Graham, 2010]

The magnitude of EPSP or IPSP is typically less than 10 mV (Figure 3-7). Therefore, a single EPSP is not sufficient to reach the threshold. However, if a few synapses produce EPSPs almost simultaneously, their summation is likely to generate a nerve impulse (Figure 3-8).


Figure 3-8. A nerve impulse may be generated when the summation of EPSP and IPSP at the axon initial segment (AIS) reaches the threshold. [Source: OpenStax]