EPSP (Excitatory Postsynaptic Potential) Graph

Here is the classic graph used to illustrate an EPSP, showing membrane potential (Vm) plotted against time, from a resting potential of -65 mV:

EPSP summation graph - single EPSP, spatial summation, temporal summation

How to read it

Y-axis: membrane potential (Vm), starting at rest (around -65 mV, shown as a dashed line).
X-axis: time.
Shape: a single EPSP looks like a rounded hump - a rapid rise (depolarization, caused by Na⁺ influx through ligand-gated channels opened by an excitatory neurotransmitter) followed by a slower exponential decay back to resting potential as the channels close and the membrane's leak conductance restores baseline. It never overshoots into a spike by itself; it's a graded, decremental potential, unlike an all-or-none action potential.

The three panels shown above

Panel A - single EPSP: One presynaptic action potential arrives, releases neurotransmitter, and produces one modest EPSP hump that rises and decays back to baseline.
Panel B - spatial summation: Several synapses on the dendrite are activated simultaneously (different presynaptic axons firing at the same time). Their individual EPSPs add together, producing a taller combined peak than any single EPSP alone.
Panel C - temporal summation: A single synapse fires repeatedly in rapid succession (within about 15 ms, before the prior EPSP has fully decayed). Each new EPSP "piles on top" of the previous one's still-decaying tail, producing a staircase-like climb toward threshold.

Both summation mechanisms are how a neuron integrates weak, subthreshold inputs into a depolarization large enough to cross threshold at the axon hillock and fire an action potential - Neuroscience: Exploring the Brain, 5th ed., Fig. 5.23, p. 439-440.

EPSP vs IPSP and real ganglionic recording

In a real neuron, EPSPs (depolarizing, Na⁺-driven) and IPSPs (hyperpolarizing, typically Cl⁻ or K⁺-driven) can occur in sequence. A well-known physiology figure records this from an autonomic ganglion cell: two EPSPs occur after ACh release (the first subthreshold, the second suprathreshold and triggering a spike), followed by a slower IPSP, then a slower muscarinic EPSP, and even a slower peptide-mediated EPSP - illustrating how a single postsynaptic cell integrates multiple, overlapping graded potentials of different time courses - Ganong's Review of Medical Physiology, 26th ed., Fig. 13-4, p. 269.

If you meant something different by "EPSP graph" - for example, a field EPSP (fEPSP) slope-vs-time plot used in long-term potentiation (LTP) experiments, or you want it for a specific exam/course context - let me know and I can pull that specific version.

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