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The term sagittal refers etymologically to the median suture between the right and left parietal bones of the cranium, known classically as sagittal suture, because it looks roughly like an arrow by its confluence with other sutures (sagitta; arrow in Latin).Histochemistry uses knowledge about biochemical reaction properties of the chemical constituents of the brain (including notably enzymes) to apply selective methods of reaction to visualize where they occur in the brain and any functional or pathological changes.In the early 1970s, Sydney Brenner chose it as a model system for studying the way that genes control development, including neuronal development.One advantage of working with this worm is that the nervous system of the hermaphrodite contains exactly 302 neurons, always in the same places, making identical synaptic connections in every worm.The first known written record of a study of the anatomy of the human brain is the ancient Egyptian document the Edwin Smith Papyrus.The next major development in neuroanatomy came from the Greek Alcmaeon, who determined that the brain and not the heart ruled the body and that the senses were dependent on the brain.Brenner's team sliced worms into thousands of ultrathin sections and photographed every section under an electron microscope, then visually matched fibers from section to section, to map out every neuron and synapse in the entire body, to give a complete connectome of the nematode.
Immunocytochemistry is a special case of histochemistry that uses selective antibodies against a variety of chemical epitopes of the nervous system to selectively stain particular cell types, axonal fascicles, neuropiles, glial processes or blood vessels, or specific intracytoplasmic or intranuclear proteins and other immunogenetic molecules, e.g., neurotransmitters.
In vertebrates, the nervous system is segregated into the internal structure of the brain and spinal cord (together called the central nervous system, or CNS) and the routes of the nerves that connect to the rest of the body (known as the peripheral nervous system, or PNS).
The delineation of distinct structures and regions of the nervous system has been critical in investigating how it works.
For several hundred years afterward, with the cultural taboo of dissection, no major progress occurred in neuroscience.
However, Pope Sixtus IV effectively revitalized the study of neuroanatomy by altering the papal policy and allowing human dissection.
For information about the typical structure of the human nervous system, see human brain or peripheral nervous system.