Neuropore

NEUROPORE, the opening at the end of the neural tube. After the neural plate separates from the ectoderm, it folds into a tube that gradually closes. The closure of the neural tube begins in the region of the future midbrain and from there spreads in both cranial and caudal directions. At the anterior and posterior ends, the neural tube remains unclosed, and the openings thus formed are called the anterior, resp. posterior neuropore. The anterior N. opens to the exterior and connects the cavity of the neural tube with the external environment, while the posterior one opens into the cavity of the primitive intestine (canalis neurentericus, blastoneuropore). The existence of the anterior N. is short-lived, but after its closure, the anterior end of the brain for some time retains a conical protrusion in the place of the former N., which is called processus neuroporicus, and the cavity of this appendage is called recessus neuroporicus, s. recessus olfactorius impar, s. recessus triangularis. The ectoderm at the site of N. closure forms a thickening - the unpaired olfactory plate, the so-called 'placode'. Gradually, in connection with the growth of the brain walls, pr. neuroporicus is smoothed out. In a human embryo, the N. is widely open at two weeks of age (with an embryo length of 3.2 mm). At about three weeks, the neuropore closes.