Development of the brain

The 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 function.

Initially, 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).