Neurobiology BIOL 4370
Monday September 16 , 2013
Two thirds of all gene expression occurs for the brain. The age of the embryo
in weeks – has critical times (purple portion before). Development has a
critical period and continues
Schizophrenia – involves the early period of development of the nervous
system, there are “critical” stages. The critical period, myelination is out of
balance, which causes schizophrenia.
At the early blastula stage – early in development, it is a cell mass, has a
polarity, has endoderm, and mesoderm. The animal pole has more
proliferation versus the vegetal pole.
Neurulation occurs at 18 days – neuroectoderm, notochord (which develops
into spinal cord and releases factors that effects differentation), primitive
streak, which is the early nervous system. At day 20, the cells are more
differentiated, the neural crest form, which is the early PNS. The floorplate=
base of the NS, and the somites =muscular system is formed as well.
At 22 days – roofplate is found, neural crest is separated. At 24 days- somite
packages form, first signs of sensory ganglion cells, which are present adjacent
to the spinal cord. Sensory ganglions are the relay center of the sensory
nerves. (*Dorsal horn = sensory input, and Ventral horn = output.)
mesenchymal cells become the spinal cord. Many different cell types, of the
1. Sensory cells
2. Autonomic ganglia *digestive cells
3. Adrenal neurosecretory cells – part of the nervous system that makes
4. Non-neural tissue, ie. melanocytes
Spina bifida – Improper closure/fold of spinal arches, neural tube. Occulta,
which is hidden, not visible. Aperta which is visibly present.
Symptoms: physical complications, academic skills, social competence etc.
How the brain is developed, how the CNS emerges from the neural tube
Proliferation and differentiation of cells and increasing pressure,which
enlarges parts of a simple neural tube. At this point prosencephalon,
rhombencephalon and mesenscephalon are present.
Hox genes has arrangements in clusters and by differential expression of
groups of genes patterns are created along the axis. Coordinated gene
expression and cell differentiation. Segments at the rhombencephalon are expressed longitudinally down the axis and then outwards laterally to the
peripheries. The combination of gene expression and cellular differentiation
occurs specifically for each of the developing nerves. Motor cranial nerves are
found in the medially, sensory cranial nerves are found laterally, and there is a
mix of both found in between
Molecular basis of neural induction
At this stage there are a diffusion of gradients that drives differentiation,
diffusible factors are found along the floorplate of the neural tube.
Three types of signaling pathways:
1. Diffusible factor which crosses cell membranes and reaches adjacent
into a cell, which binds to a RA-binding protein which goes into the
2. Fibroblast growth factor – binds to receptor tyrosine kinase which
causes a cascade within the cell, which then goes into t