This is a 2D cross-section counterpart to the 3D neural-tube simulator: instead of an animated grid, it models one slice of the neural plate as a chain of 24 connected trapezoid cells. Each cell has a fixed basal (outer) edge width — the outer lamina does not stretch — and a variable apical (inner, lumen-facing) edge width that narrows under actomyosin constriction, exactly as real hinge-point cells do.
For a cell whose basal width is b, apicobasal height h, and apical width a, wedging that trapezoid bends the local sheet by the real trapezoid exterior angle:
bend angle = 2 · atan( (b − a) / (2h) )
The simulator computes a for every one of the 24 cells from its distance to the nearest hinge center (median, or one of the two dorsolateral) and the current constriction strength and folate factor, converts each cell's own apical:basal ratio into its own bend angle with the formula above, then walks the chain summing those 24 bend angles to trace out the folded cross-section — the curvature is a genuine consequence of per-cell geometry, not a scripted target shape.
- Closure is measured directly as the distance between the two free ends of the folded chain: the tube is "closed" only when that gap shrinks below 12% of the flat plate width, which this model reaches once combined hinge constriction is pushed past roughly 85% strength — real neurulation likewise fails outright at partial constriction, not gradually.
- Median vs. dorsolateral role: in the intact embryo, caudal (future spinal cord) segments lean more on the median hinge, while cranial (future brain) segments lean more on the dorsolateral hinges — so on this single cross-section, an MHP-limited fold stands in for a spina-bifida-type failure mode and a DLHP-limited fold stands in for an anencephaly-type failure mode.
- Folate multiplies both hinges' constriction level, matching its systemic role fueling the DNA synthesis and methylation hinge-point cells need to constrict on schedule.
Like its 3D sibling this is a simplified kinematic model, not a tissue-mechanics PDE — but the wedge-cell geometry, the width-ratio→curvature relationship, and the sharp constriction threshold for closure are drawn directly from developmental biology.