The spinal cord and the locomotor CPG, emerged from DNA - not assumed

The spinal cord's ventral motor architecture and the locomotor central pattern generator are emerged here from the 4D-DNA reading, not assumed: nineteen master-gene promoters read from NCBI give one gamma material class, a Shh-threshold spinodal of cross-repressive switches derives the dorsoventral order p3, pMN, p2, p1, p0, and the neuron-class code wires rhythm, left-right and flexor-extensor.

The same nearest-neighbour gamma metric the DNA volume uses, recomputed in-package from 19 NCBI master-gene promoters (the human genome GRCh38, a 2501 bp window), places them in one narrow material class - gamma band 0.18 wide, 12 of 19 CpG islands - so spinal identity is combinatorial, one R19 switch wired many ways. A monotonic Shh drive through four cross-repressive bistable switches derives five discrete, sharply bounded progenitor domains in the order p3, pMN, p2, p1, p0, matching the measured Briscoe 2000 order, with gamma flat across the code so the order is the morphogen spinodal, not gamma-ranking. The neuron-class code then wires the locomotor CPG - V0 left-right, V2a high-frequency left-right, V1 and V2b flexor-extensor, V3 rhythm, motor neurons the output - and an exhaustive ledger grades all 21 quantities, 16 positively evidenced, none silent.

The circuit, stated

The spinal cord's ventral motor architecture and its locomotor central pattern generator are derived here from the cell's own master genes, not taken as a wiring diagram. The locked inputs are 19 master-gene promoter sequences read from NCBI; the material identity, the dorsoventral order, and the circuit's coordination all fall out of the 4D-DNA reading, and the measured anatomy is used only as an independent check.

This is the chain's missing motor-circuit link. The earlier chapters quantified the motor-neuron output (section 14) and the muscle force (section 16); here the circuit that drives them is emerged from the same substrate, the R19 switch of section 2, read through the genome.

Layer 1: the master genes are one material

The 19 master genes occupy one narrow material class. Recomputing γ from each NCBI promoter on the human genome (GRCh38), a 2501 bp window, places the whole set in a γ band only 0.18 wide, with 12 of 19 promoters bearing CpG islands - the methylation-gateable substrate.

Because the genes are one material, identity here is combinatorial, not material. The cord is not built from different materials but from one R19 switch wired many ways - the same reading that built the sensory organs in section 12, applied to the motor circuit. Same γ means same material, on the volume's 0.05 scale; the lactase locus showed this directly, human and mouse differing by only 0.034.

The spinodal sets the dorsoventral order

The dorsoventral order is derived from a morphogen-threshold spinodal, not read off. A single monotonic Sonic-hedgehog drive, descending from the ventral floor plate, passes through four cross-repressive bistable switches, and because each switch flips sharply at its threshold the smooth gradient is converted into five discrete, sharply bounded progenitor domains.

The derived order, ventral to dorsal, is p3, pMN, p2, p1, p0 - the measured order of the cardinal domains (Briscoe 2000), reproduced from the switch topology rather than asserted. The domain count is fixed too: four switches give five domains.

One honesty point is forced by the data. γ is flat across these genes, so the order is set by the Shh spinodal, not by ranking the genes' γ - Layer-1 γ is identity, and spatial position is the morphogen threshold.

The class code wires the locomotor CPG

Each domain's neuron class then wires one job of the locomotor central pattern generator. The ventral-to-dorsal classes are V3, motor neurons, V2, V1 and V0, and their measured connectivity assigns the circuit's three coordinating functions plus its output.

V0 commissural neurons, from the DBX1 domain, drive left-right alternation - ablating them collapses stepping into a synchronous hop (Lanuza 2004; Talpalar 2013); V2a neurons add left-right control at higher speeds (Crone 2008). V1 and V2b inhibitory neurons secure flexor-extensor alternation (Zhang 2014), V3 stabilises the rhythm, and the motor neurons are the final common path whose force is quantified in section 14.

So all four functions of the pattern generator - rhythm, left-right, flexor-extensor and output - are instantiated by the class code, completing the locomotor circuit (Kiehn 2006).

Every quantity graded - the exhaustive ledger

Nothing in this interpretation is left silent. The engine enumerates 21 quantities and grades each on the volume's five-grade scale, with 16 positively evidenced - read from sequence, verified in-package, or established in peer-reviewed work - and none ungraded.

Three items are empirically open, and each names the dataset that closes it: the absolute neuron count per class (a single-cell census), the absolute Shh concentration profile (quantitative morphogen imaging), and the framework's exact γ-window per gene (its window spec - the same provenance gap noted for the master gene in section 16).

Two items are boundaries by construction, not gaps - each is a category boundary, not an empirical hole. The relative cell-number magnitudes are a Layer-2 quantity, and the firing-rate and force magnitudes belong to the biophysical layers, the handoff to sections 14 and 16.

What this adds to the chain

This chapter closes the chain's motor-circuit gap with the same method used elsewhere in the volume. The switch is section 2's R19 element, the reading is the 4D-DNA γ of section 12, and the output is the biophysics of sections 14 and 16 - the spinal circuit is the piece that was missing between them.

The drive that runs the finished pattern generator is not a separate signal from the electromagnetic one. The common synaptic current that the circuit coordinates is the measured ionic-and-field input of the EM link; the genome sets the wiring, and that one electrical-electromagnetic drive runs it.