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Summary Adaptive brain chapter 22
This document contains a summary of the lectures and book Purves Neuroscience, about chapter 22 “Early brain development”.
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Early brain development chapter 22The cells that will generate the nervous system become distinct Neurulation of the embryo takes place to enclose the layers from
early in the generation of the embryo, concurrent with the the middle in the cranial-caudal way (from the middle to the
establishment of the midline and the basic body axes: anterior- head and tail). Sometimes this goes wrong and which causes
posterior (mouth-anus), dorsal-ventral (back-belly), and medial- meningomyelocele where the back is still exposed due to wrong
lateral (midline-periphery). In addition, the unique curvature of closing. Other neural tube defects such as anencephaly cause no
the human CNS generates a distinctive rostral-caudal axis (nose- brain to develop and exencephaly cause the brain to develop
tail) in the developing brain. outside of the body.
Gastrulation Formation of the major brain subdivisions
The zygote develops into an eight-cell state, which is then cleaved After the neural tube forms the tube bends and folds to form
to form a Blastula, which is a hollow ball. The hollow ball the major brain regions. The prosencephalon gives rise to the 6
invaginates and forms 3 different germ layers. The ectoderm is forebrain segments, the mesencephalon gives rise to the midbrain
the outside layer that later develops into the skin (epidermis) and and the rhombencephalon gives rise to the 8 hindbrain segments.
the nervous system. The layer that is underneath the ectoderm is Caudal to the cervical flexure, the neural tube forms the
the mesoderm, which later develops into skeletal, muscular and precursor of the spinal cord. The bending and folding diminish or
cardiovascular systems. The inner layer is the endoderm, which enlarge certain structures that eventually become the different
develops into all the tube-like structures in the body, such as the ventricles of the mature brain.
urinary tubes and the digestive system.
Neurulation
The notocord is a vertebral column that is involved in the
formation of the neural tube and consists of mesodermal cells. As
a result of these cell movements, the notochord defines the
embryonic midline, and thus the axis of symmetry for the entire How are these brain structures produced?
body. The notochord eventually disappears once the early Part of the answer comes from an observation, made in the early
development is complete. The notochord is involved in early neural 20th century, that the neural tube is organised into repeating
differentation and sends inductive signals to innitiate the units called neuromeres and that the animal embryos are
invagination and to the overlying ectoderm that causes cells to segmented. They observed this in the fruit fly, Drosophila, in this
differentiate into neuroectodermal percursor cells, this process is fly the early expression of Hox genes guides the differentiation
called neurulation. The midline ectoderm that contains these cells of the embryo into distinct segments that give rise to the head,
thickens into a columnar epithelium called the neural plate, which thorax, and abdomen.
invaginates to form the neural tube. There are also other cells
formed, called crest cells that eventually migrate and develop into
the peripheral nervous system (sensory ganglia, autonomic
ganglia, adrenal chromaffin cells, and melanocytes). The notochord
remains later develop into the vertebrate column.
These Hox genes code for transcription factors that help change
the gene expression of other genes that mediate morphogenesis
(Hox, Pax, Msx, etc). Morphogens are these inductive signals that
are produced by surrounding cells that induce the expression of
the transcription factors. Example: the notochord produces
chordin.
Teratogens
This is am agent that causes malformation in embryos, happens
when the inductive signals are a little bit different in
concentration, which causes developmental deficits in the brain.
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