Neurulation converts the flat neural plate into the neural tube by concentrating curvature at three hinge lines running the length of the plate: one median hinge point (MHP) at the ventral midline and two dorsolateral hinge points (DLHP). At each hinge, actomyosin rings constrict the apical (outer) surface of the neuroepithelial cells while the basal surface stays wide, wedging each cell and forcing the sheet to bend there — everywhere else the epithelium stays comparatively flat and just rotates rigidly.
This simulator treats one cross-section as a chain of rigid segments that turns only at the three hinges. If θMHP and θDLHP are the cumulative bend angles contributed by each hinge, the sheet closes into a tube exactly when the total turning satisfies the closed-curve condition:
θ_MHP + 2·θ_DLHP → 2π (360°)
θ_MHP ∝ MHP constriction × folate factor
θ_DLHP ∝ DLHP constriction × folate factor
If the total turning falls short of 2π, the two neural folds never meet at the dorsal midline and a gap — a neuropore — remains, which is rendered here as the literal endpoint separation of the folded chain.
- Closure is a zippering wave, not instantaneous: it starts near the hindbrain/cervical boundary and runs both rostrally and caudally, closing the anterior neuropore first (~day 24 in humans) and the posterior neuropore last (~day 26–28).
- Cranial segments lean on DLHP more than caudal segments do, and caudal segments lean on MHP more — so insufficient DLHP constriction here preferentially leaves the anterior end open (an anencephaly-type pattern), while insufficient MHP constriction preferentially leaves the posterior end open (a spina bifida-type pattern), mirroring the real regional biology.
- Folate is a systemic multiplier on both hinges: it is required for the rapid DNA synthesis and methylation that let hinge-point cells constrict on schedule, which is why periconceptional folic-acid supplementation measurably lowers neural tube defect rates.
This is a simplified kinematic model of a real biomechanical process, not a literal PDE simulation of tissue mechanics — but the closure geometry, the hinge-point roles, and the anterior/posterior defect asymmetry are drawn directly from developmental biology.