8. Neurons and Other Excitable Cells

Calcium plays a major role in every neuron. Not only does it play a part in controlling the membrane potential, but it is also a crucial ingredient of both the pre-synaptic and post-synaptic terminals. At the pre-synaptic terminal the secretion of neurotransmitter is controlled by Ca²⁺, as is short-term plasticity, while in the post-synaptic terminal Ca²⁺ is both necessary and sufficient for long-term synaptic plasticity, i.e., long-term depression, long-term potentiation, and spike-timing-dependent plasticity. In neuroendocrine cells from the hypothalamus and pituitary, as well as in the endocrine pancreas, Ca²⁺ controls the membrane potential, the shape of the bursts of electrical spiking, and the secretion of hormones. In photoreceptors and olfactory receptors, Ca²⁺ is at the centre of the biochemical networks that control adaptation to a maintained stimulus, while in interstitial cells of Cajal Ca²⁺ controls the membrane potential in ways that we do not yet fully understand. There are many other examples of the importance of Ca²⁺ in neurons and excitable cells.