The brain and spinal cord develop from a structure in the early embryo called the neural tube.About three weeks after fertilisation, a strip of ectoderm along the back of the embryo thickens to form the neural plate. The edges of the plate rise up as neural folds, which curl towards each other and fuse, forming a hollow neural tube. This process is called neurulation. If the tube does not close properly, conditions such as spina bifida can result, which is one reason folic acid is recommended in early pregnancy.By about four weeks, the front end of the tube has swollen into three primary brain vesicles:• the forebrain
• the midbrain
• the hindbrainThe rest of the neural tube becomes the spinal cord. The hollow centre of the tube remains as the fluid-filled ventricles of the brain and the central canal of the spinal cord.These regions then develop further. The forebrain forms the cerebrum (cerebral hemispheres), the thalamus and the hypothalamus. The midbrain stays relatively small. The hindbrain forms the cerebellum, the pons and the medulla oblongata.Cells lining the tube divide rapidly by mitosis to produce huge numbers of neurones. The new neurones migrate to their final positions, grow axons and dendrites and form synapses. Far more neurones and synapses are made than are needed, and those that are not used are removed. Which connections survive depends partly on the stimulation the brain receives.In humans the cerebrum grows so much that it covers most of the rest of the brain, and it becomes highly folded, giving a large surface area inside the skull.
• the midbrain
• the hindbrainThe rest of the neural tube becomes the spinal cord. The hollow centre of the tube remains as the fluid-filled ventricles of the brain and the central canal of the spinal cord.These regions then develop further. The forebrain forms the cerebrum (cerebral hemispheres), the thalamus and the hypothalamus. The midbrain stays relatively small. The hindbrain forms the cerebellum, the pons and the medulla oblongata.Cells lining the tube divide rapidly by mitosis to produce huge numbers of neurones. The new neurones migrate to their final positions, grow axons and dendrites and form synapses. Far more neurones and synapses are made than are needed, and those that are not used are removed. Which connections survive depends partly on the stimulation the brain receives.In humans the cerebrum grows so much that it covers most of the rest of the brain, and it becomes highly folded, giving a large surface area inside the skull.