Acronym: Br
The term brain refers to one of two parts of the central nervous system (CNS) as defined by dissection in vertebrates. It is the part of the CNS located in the cranial cavity; the other part is the spinal cord. (Some biologists also use 'brain' in reference to the central ganglion of the nervous system of invertebrate species ( Wikipedia )).
     Neuroanatomists subdivide the brain in three different ways. Most textbooks and brain atlases are organized according to the Classical Model, which at the highest level divides the brain into forebrain, midbrain and hindbrain. Below that level structures are grouped by proximity as the brain is dissected to finer and finer levels. The Classical Model is reflected in the hierarchy of human and macaque brain structures that you find when you click 'Locus in Brain Hierarchy' below. It is reflected for the rhesus macaque brain in the Macaque Brain by Dubach, which you find by clicking 'Models Where It Appears' below.
     The definition of the brain in the second model, the Developmental CNS Model, differs from the Classical Model in that structures are grouped by the location of their precursors in the embryo; and it includes the retina, a structure which is located outside the cranial cavity of the mature animal but originates in the Encephalon (embryonic brain). (The retina is classically defined as part of the peripheral nervous system.) To avoid confusion, the standard NeuroNames terminology for structures defined by dissection of the mature brain are in English; standard names for subdivisions based on embryonic precursor are in Latin and capitalized. Thus, the highest level divisions of the Developmental CNS Model are the Telencephalon, Mesencephalon, and Rhombencephalon, which correspond to a large extent, but with significant exceptions, to the forebrain, midbrain, and hindbrain of the Classical Model. (The Developmental CNS Model is not currently illustrated in BrainInfo.)
     In the third model, the Functional CNS Model, structures are grouped by a combination of criteria, including embryonic origin, internal structure, connectivity, and function. Division at the highest level is into four structures: the pallium, subcortical nuclei, cerebellum, and cerebrospinal trunk. (The pallium consists of the cerebral cortex and the cortical subplate nuclei.) In the Functional Model the retina is a component of the cerebrospinal trunk. The concept 'brain' does not actually appear in the Functional CNS Model, because there is no functionally meaningful basis for distinguishing the part of the cerebrospinal trunk located in the cranium from that enclosed in the spinal column.
     The hierarchical organization of the Functional Model is derived almost entirely from appendices to the atlas of the rat brain in Swanson-2004 . To see it, click: Functional CNS Model - Rat. The NeuroNames terminology for structures in the Functional Model is, insofar as possible, the same as that for structures that are equivalent to structures in the Classical Model.
     Each of the three models is more useful than the others for certain purposes. The Classical Model is most useful for understanding the terminology of the neuroanatomical literature of the past century and for surgical and radiological applications, which involve dissection and/or visualization according to classical landmarks. The Developmental Model is more useful for analyzing the embryonic and genetic origins of brain structure. The Functional Model is most useful for addressing the fundamental challenge of neuroscience, namely to understand the relations between neural structure and function.
     In that context, the primary purpose of BrainInfo/NeuroNames is to clarify the relations between the structural concepts and the terminologies of these and other ways of looking at the central nervous system.

Also known as: suprasegmental structuresNeuroNames ID : 21

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