Neurotransmitter release occurs when presynaptic depolarization opens calcium channels and calcium triggers vesicle fusion with the presynaptic membrane, linking cellular mechanisms to rapid communication in nervous systems.
Coverage 2017–2025 · Updated 15 Jul 2026
Arrival of an action potential at a presynaptic terminal opens voltage-gated calcium channels and triggers vesicle fusion.
Ca²⁺ entry binds release machinery, causing exocytosis of neurotransmitter into the synaptic cleft. Enzymatic breakdown, reuptake or diffusion then terminates the signal. This one-way sequence explains why changing calcium entry can alter how strongly a synapse communicates.
Trace release:
Blocking presynaptic calcium entry reduces transmitter release even if the action potential still reaches the terminal.
The electrical impulse triggers release; it does not cross the cleft as the same electrical current.
This objective is assessed through structured response, commonly using Describe / Explain / Outline.
Describe / Explain / Outline / Deduce / Label / State
Build the answer around this relationship: An arriving action potential depolarizes the presynaptic terminal.
Representative question
Describe how neurotransmitters are released from a presynaptic neuron membrane.
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.
