Proteins in the neural tissues of this zebrafish embryo direct cells to line up and form the neural tube, which will become the spinal cord and brain. Studies of zebrafish embryonic development may help pinpoint the underlying cause of common neural tube defects - such as spina bifida - which occur in about 1 in 1,000 newborn children. (NIGMS) Image credit: Alexander Schier, Harvard University.

Nervous System Development: the nervous system develops in segments similar to those of simpler animals, such as segmented worms. The segments in the head expand and fuse together, forming the “cerebral hemispheres” and “brainstem.” (Blumenfeld, 22)

In humans, as it other vertebrates, the "brain" begins as part of the “neural tube.” The generation of the cells that will eventually form the “cerebral cortex” begins about 7 weeks after conception and is largely complete by 20 weeks. (Kolb, 195) Knowledge-specific cortical regions mature at different rates. For example, the “fusiform area” of the “visual cortex,” which responds to faces, triples in size between ages 8 and 20, as does the “parahippocampal place area," which responds to location. The lateral “occipital cortex,” which responds to objects, changes very little (during this period). (Memory and Mind, John Gabrieli)


Neural Plate: flat sheet of (“tissue”) that will roll up to form the neural tube of a "vertebrate" "embryo." (SDBCoRe) The strip of “ectoderm” lying along the central axis of the early embryo that forms the neural tube and subsequently the “central nervous system.” (OxfordMed) Three weeks after conception, (this) primitive neural tissue occupies part of the outmost layer of embryonic cells. The neural plate first folds to form the ‘neural groove.’ The neural groove then curls to form the neural tube. (Kolb, 190-191)

Neural Tube: process whereby the embryo internalizes its developing nervous system. (Patestas, 12) The multistep embryological process responsible for initiating central nervous system formation. Occurs just after “gastrulation” and involves the formation of the neural tube from ectoderm located “dorsal” to the “notochord.” All "neurons" and their supporting cells in the central nervous system originate from neural "precursor" cells derived from the neural tube. (Booker, 1116) By the twenty-eighth day, the neural tube seals up, completely isolating it from the outside world. (Bainbridge, 44)

Notochord: a strip of “mesodermal” tissue that develops along the dorsal surface of the early embryo, beneath the neural tube. It becomes almost entirely obliterated by the development of the “vertebrae,” persisting only as part of the "intervertebral discs." (OxfordMed) Cartilage-like rod which comprises the dorsal-most part of the mesoderm of a vertebrate embryo. (SBECoRe) A slender rod of cells of mesodermal origin running along the back of the early embryo and which directs formation of the neural tube. In vertebrates, it is replaced by the spinal column. (Lawrence)

Pre-Central Nervous System Development: (period during which) the neural tube is subdivided into three “morphologically” recognizable components. (Patestas, 21) By the thirtieth day in humans, the top end of the neural tube has swollen into three little hollow bulges, the "forebrain," "midbrain," and "hindbrain," the last of which connects to the spinal cord. Next, the brain starts to progress further into a five-bulge structure. Two lobes start to grow out of the left and right side of the forebrain bulge, drawing a part of the fluid-filled space inside the brain with them. They are referred to as the ‘endbrains’ or the “telencephalon.” Next, (the bulge that is the hindbrain) starts to divide into the upper “pons” and lower “medulla.” These two latter regions are also called the “metencephalon.” At this early stage the brain is growing faster than the head that imprisons it. Because of this it must fold and twist just to fit inside the head. (Bainbridge, 47-49) A globular structure soon starts to bulge out at the top end of the “fourth ventricle.” Because of its size and the convolutions that form on its surface, this bulge is called the “cerebellum,” or ‘little brain.’ (Bainbridge, 52)

Forebrain: the “anterior” of the three primitive (sacs) of the embryonic brain arising from the neural tube. It subdivides to form (the) “diencephalon” and (the) “telencephalon.” (MeSH) The furtherest forward division of the brain, consisting of the telencephalon and the diencephalon. (OxfordMed) By the thirtieth day in humans, appears as a little hollow bulge in the neural tube. (At this stage referred to as the ‘prosencephalon.’) (Bainbridge, 47-48) Sits on top of the midbrain, pons, and medulla, almost like a cauliflower on its stalk. (Blumenfeld, 15) Includes the “basal ganglia” and the “limbic system.” (Kolb, 52) The largest part of the brain. Credited with the highest intellectual functions (BrainFacts) Evolutionary studies have shown that all vertebrates probably share the same basic arrangement of the forebrain, but that different regions are emphasized in different groups (Bainbridge, 277) Also referred to as ‘prosencephalon.’

Hindbrain: the “posterior” of the three primitive (sacs) of an embryonic brain. It consists of (areas) which develop the major brain stem components, such as “medulla oblongata,” cerebellum, and pons, with an expanded cavity forming the fourth ventricle. (MeSH) Contains the structures that coordinate and control most voluntary and involuntary movements. Evolutionarily the oldest part of the brain. (Kolb, 49) There is no clear boundary between the pons and medulla, they merge imperceptibly into each another. (Bainbridge, 47-48) Also referred to as ‘rhombencephalon.’

Midbrain: region of the embryonic vertebrate brain that will become the 'optic tract.' (SBECoRe) The middle of the three primitive cerebral vesicles of the embryonic brain. Without further subdivision, the midbrain develops into a short, constricted portion connecting the pons and the diencephalon. (MeSH) With the pons and medulla, the midbrain is involved in many functions, including regulation of "heart rate," "respiration," pain perception, and movement. (BrainFacts) Central part of the brain that contains neural “circuits” for hearing and seeing as well as orienting movements. (Kolb, 49) Also referred to as ‘mesencephalon.’