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For example it can be expressed as molar fraction, volume fraction, mass fraction, molality, molarity or normality.Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equals the total mass of the products leading to the insight that the relations among quantities of reactants and products typically form a ratio of positive integers.Again in this case, the situation is different for swimming, creeping or quadrupedal (prone) animals than for Man, or other erect species, due to the changed position of the axis.A mid-sagittal plane divides the body and brain into left and right halves; sagittal sections in general are parallel to this median plane, moving along the medial-lateral dimension(see the image above).Chemical composition, also known as chemical makeup or simply, composition, is a concept in chemistry that has different, but similar, meanings if referred to a single pure substance or a mixture.The chemical composition of a mixture can be defined as the distribution of the single substances that constitute the mixture, called "components".For information about the typical structure of the human nervous system, see human brain or peripheral nervous system.This article discusses information pertinent to the study of neuroanatomy.
Herophilus and Erasistratus of Alexandria were perhaps the most influential Greek neuroscientists with their studies involving dissecting the brains.
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.
The brain is small and simple in some species, such as the nematode worm, where the body plan is quite simple: a tube with a hollow gut cavity running from the mouth to the anus, and a nerve cord with an enlargement (a ganglion) for each body segment, with an especially large ganglion at the front, called the brain.
The nematode Caenorhabditis elegans has been studied because of its importance in genetics.
The first known written record of a study of the anatomy of the human brain is the ancient Egyptian document the Edwin Smith Papyrus.