An excitatory postsynaptic potential forms when neurotransmitter binding opens ion channels and depolarizes the postsynaptic membrane toward threshold, linking cellular mechanisms to rapid communication in nervous systems.
Coverage 2014–2021 · Updated 15 Jul 2026
An excitatory postsynaptic potential (EPSP) is a graded depolarization that makes the postsynaptic neuron more likely to reach action-potential threshold.
Neurotransmitter released from the presynaptic terminal diffuses across the synaptic cleft and binds a transmembrane receptor. Acetylcholine can open ligand-gated channels, allowing net positive charge to enter and depolarize the postsynaptic membrane.
Sequence: transmitter release → diffusion across cleft → receptor binding → channel opening → local depolarization. Acetylcholine acts at many synapses, including neuromuscular junctions.
One acetylcholine input may produce a small EPSP below threshold; overlapping excitatory inputs can sum at the axon hillock until an action potential is triggered.
An EPSP is local and graded, not an all-or-none action potential. The neurotransmitter does not carry the electrical impulse across the cleft; receptor-controlled ion movement changes voltage.
This objective is assessed through structured response, commonly using Explain / Describe.
Explain / Describe
Build the answer around this relationship: Excitatory neurotransmitters bind receptors on the postsynaptic membrane.
Representative question
Describe how an excitatory postsynaptic potential is generated.
Up to one additional mark is available for the construction of your answer.
Neurons carry electrical impulses in the nervous system; motor, sensory, and relay neurons differ in axon, dendrite, and cell body arrangement. Sodium-potassium pumps use ATP to move 3 Na+ out and 2 K+ in; ion gradients make the resting axon polarized at about -70 mV. A nerve impulse is a propagated action potential along a nerve fibre; stimulus-triggered sodium influx reverses membrane polarity. Larger axon diameter lowers resistance and increases impulse speed; myelin sheaths and nodes of Ranvier enable faster saltatory conduction. Synapses connect neurons to neurons, muscles, or glands; chemical synapses transmit one way across a narrow synaptic cleft. Action potentials open voltage-gated Ca2+ channels in presynaptic terminals; Ca2+ causes vesicle fusion and neurotransmitter exocytosis into the cleft. Neurotransmitters diffuse and bind receptors on the postsynaptic membrane; EPSPs depolarize the membrane and make threshold more likely.
