Fourth week

1. 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.

2. 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.

3. Synapse formation • Known as synaptogenisis- appears 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

4. 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.

5. 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.

6. 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.

7. 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.