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Fourth week • By the fourth week, part of the neural plate has folded in on itself to form a neural tube. • Part of this eventually becomes the spinal cord and ventricles in the brain These ‘hollow’ areas contain fluid. • At this point, primitive brain cells called neuroepithelial cells begin to divide rapidly, or proliferate. About 4 weeks of age • Three bulges emerge from the top of the neural tube, eventually giving rise to the forebrain midbrain, and hindbrain. We will talk about these three areas in a minute. The rest of the neural plate becomes the neural crest, which will become the spinal cord. Synapse formation • Known as synaptogenisisappears dependent upon glial cells • Likely any given synapse is under a series of chemical signals in which each pre and postsynaptic neuron weighs a variety of synaptic-promoting and synaptic inhibiting signals before forming synapses with the best available cells Back to the structures in the growing brain 2nd and 3rd month • The growing brain is beginning to take shape. • The hindbrain gives rise to the medulla oblongata and the pons (part of the brain stem), which are involved in many functions essential to life, such as breathing and heartbeat. • The cerebellum, the part of the brain involved in maintaining balance and coordinating movement, emerges partly from the hindbrain and partly from the midbrain. 2nd and 3rd month- Forebrain development- diencephalon It is the forebrain that undergoes the most complicated changes. • The forebrain divides into two distinct structures: the diencephalon and telencephalon. • The diencephalon develops into the thalamus and hypothalamus, which will affect everything from emotions to sensory perception. 2nd and 3rd month- Forebrain development- telencephalon • • • • The telencephalon gives rise to several parts. First comes the hippocampus, which eventually will be involved in short-term memory, and other structures involved in the olfactory pathways Next, the telencephalon produces the basal ganglia, which will eventually contain structures that control movement, sensory information, and some types of learning. The amygdala will eventually help the brain attach emotional significance to signals it relays elsewhere. Late Pregnancy Nervous system developments • During the last phase of development, the earlier processes of cell proliferation and migration continue to some degree, and synapses continue to form all over the brain. • But two new processes begin in earnest: a pruning of unnecessary cells and connections - an active process, known as apoptosis, or programmed cell death (as contrasted to necrosis which is a passive process) , and the protection, known as myelination, of vulnerable neurons and connections.