Neural communication underlies all brain activity. It governs our thoughts, feelings, sensations, and actions. But knowing the importance of neural communication does not answer a central question of neu-roscience: how do individual neurons communicate? We know that communication between two neurons occurs at specialized cell junctions called synapses, at which two communicating neurons are separated by the synaptic cleft. The presynaptic neuron releases chemicals, known as neurotrans-mitters, into the synaptic cleft in which neurotransmitters bind to receptors on the surface of the postsynaptic neuron. Neu-rotransmitter release occurs in response to an action potential within the sending neuron that induces depolarization of the nerve terminal and causes an influx of calcium. Calcium influx triggers the release of neurotransmitters through a specialized form of exocytosis in which neurotransmitter-filled vesicles fuse with the plasma membrane of the presynaptic nerve terminal in a region known as the active zone, spilling neurotransmitter into the synaptic cleft.
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