EPSPistä

EPSP stands for Excitatory Postsynaptic Potential. It is a temporary, localized change in the resting potential of a postsynaptic neuron that increases the probability of an action potential. When a neurotransmitter binds to receptors on the postsynaptic membrane, it can cause ion channels to open, allowing positive ions like sodium (Na+) to flow into the cell. This influx of positive charge makes the inside of the neuron less negative, causing depolarization.

This depolarization is what constitutes the EPSP. It is a graded potential, meaning its amplitude varies depending on the amount of neurotransmitter released and the number of receptors activated. An EPSP is not an all-or-none event like an action potential; rather, it represents a subthreshold depolarization that moves the neuron closer to its firing threshold.

Multiple EPSPs from different synapses, or repeated EPSPs from the same synapse, can summate. Temporal summation occurs when a single presynaptic neuron fires multiple times in rapid succession, and the individual EPSPs overlap. Spatial summation occurs when multiple presynaptic neurons synapse on the same postsynaptic neuron and their EPSPs arrive at the dendrites at roughly the same time. If the combined effect of these summated EPSPs depolarizes the postsynaptic neuron to its threshold potential, an action potential will be generated and propagated. Conversely, an inhibitory postsynaptic potential (IPSP) causes hyperpolarization, making the neuron less likely to fire.