Information is coded in the brain as patterns of electrical impulses that are transmitted along nerve processes. These impulses are passed from one neuron to the next primarily at chemical synapses where the electrical event is converted to the release of a neurotransmitter substance that activates the next neuron in the pathway. Neurotransmitter release is triggered by the opening of ‘voltage‐sensitive’ calcium channels, the admission of a small pulse of Ca 2+ ions and the binding of these ions to the neurotransmitter secretion apparatus culminating in the fusion and discharge of a transmitter‐filled secretory vesicle. Increasing evidence suggests that most synapses an individual release site is gated by ion influx through one or more nearby calcium channels. In this section, we explore the physiology of this impulse‐to‐secretion gating mechanism. Key Concepts Information is transmitted between one neuron and the next at synapses where the nerve fibre terminal of the upstream (presynaptic) neuron contacts the surface membrane of the downstream (postsynaptic) one. Most synapses transmit by secreting a chemical neurotransmitter across the narrow space between pre‐ and postsynaptic surface membranes. Transmitter secretion is triggered by an electrical impulse that travels down the presynaptic nerve fibre to the terminal. Neurotransmitter is stored in tiny membrane ‘packets’ called synaptic vesicles which can be triggered to secrete by fusing with the presynaptic membrane at the ‘transmitter release site’. The synaptic vesicles are ‘docked’ at the release site ready for secretion. Influx of calcium ions through selective voltage‐sensitive ion channels (calcium channels) plays a key role to link the action potential to the triggering of secretory vesicle discharge. Calcium channels are positioned very close to the secretory vesicles so that when they open the spurt of entering calcium ions, called a ‘calcium domain’, can rapidly and effectively access the triggering sites for synaptic vesicle fusion.