when does the neural tube develops in a fetus
Neural tube In the developing chordate (including vertebrates), the neural tube is the embryo's precursor to the central nervous system, which comprises the brain and spinal cord. The neural groove gradually deepens as the neural folds become elevated, and ultimately the folds meet and coalesce in the middle line and convert the groove into the closed neural tube. In humans, neural tube closure usually occurs by the fourth week of pregnancy (28th day after conception). The ectodermal wall of the tube forms the rudiment of the nervous system. The centre of the tube is the neural canal.
Oogonium Oogonia are formed in large numbers by mitosis early in fetal development from primordial germ cells. In humans they start to develop between weeks 4 and 8 and are present in the fetus between weeks 5 and 30.
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Pulse Pressure waves generated by the heart in systole move the arterial walls. Forward movement of blood occurs when the boundaries are pliable and compliant. These properties form enough to create a palpable pressure wave.