of the brain
nervous system develops as a specialisation of tissue known as ectoderm.
The brain starts as a simple tube formed by invagination of the ectodermal
layer along the dorsal midline of the embryo. This tube begins to show
specialised regions at about 4 weeks of development. Differentiation of
ectodermal cells into neuroectoderm (ie cells which will further differentiate
into neurons and glial cells of the brain) is under the control of a primitive
molecular signalling pathway known as the Notch/Delta pathway.
Notch and Delta are cell surface receptors
located on neuroblasts and dermoblasts of the developing embryo. These
proteins are of particular interest because the presenilins (associated
with Alzheimer's disease) are somehow involved in the regulation of their
the neuroectoderm develops to form a tube, called the neural tube. The
lumen of this tube develops into the ventricular system of the brain and
spinal cord, whereas the tube itself develops into the brain and spinal
cord. The neural tube develops into distinct regions which are called the
telencephalon (this region will develop later into the cerebral hemispheres),
the diencephalon (develops into the thalamus), the mesencephalon (develops
into the midbrain) and the rhombencephalon (develops into the pons, medulla
and spinal cord).