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1-3 Neurons and Synapses

The concept of the "neuron" was established over a century ago as the unitary component of neuronal circuits. RamÓn y Cajal (1852–1934), hereafter shortened to "Cajal," presented clear evidence for this in 1888, when referring to the relationship between Purkinje and basket cells in the cerebellum (see below and Color Plate IV) (Lopez-Munoz et al., 2006). Heinrich von Waldeyer-Hartz (1836–1921) formally proposed the neuron theory in 1891. Also, near the end of the nineteenth century, Sherrington and Michael Foster (1836–1907) coined the term "synapse" and spotlighted it as a key structure of the CNS. Since then, neurons and synapses have been the major targets of neuroscience investigations. All neurons commonly have somata extruding axons and dendrites (except for dorsal root ganglion cells, which have no dendrites). Dendrites not only expand the membrane area to accommodate many hundreds of synapses, but they also have finely compartmentalized functions (Hausser and Mel, 2003). On the other hand, different types of neurons are distinguished by their characteristic morphology, spike activities, synaptic actions (excitatory or inhibitory), and synaptic receptiveness (chemical or electrical). Subcellular structures such as postsynaptic density (PSD), cytoskeleton, endoplasmic reticulum, Golgi organ, and mitochondrion support these neuronal functions. Signal transduction involves various transmitters, modulators, receptors (ionotropic or metabotropic, or both), and second messengers. For these molecular mechanisms of neurons, numerous proteins, glycoproteins, and lipids, and their genes play essential roles.

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