Why is the spinal cord's grey matter inside, the reverse of the brain's cortex, and what does it do there? · Grey Matter

In the cord the grey matter forms a central H, with sensory neurons in the back horns and motor neurons in the front horns, and the white matter around it is made of the long tracts that run between the body and the brain.

Why is the spinal cord's grey matter inside, the reverse of the brain's cortex, and what does it do there?

In the cord the grey matter forms a central H, with sensory neurons in the back horns and motor neurons in the front horns, and the white matter around it is made of the long tracts that run between the body and the brain. The layout keeps the local circuits compact, where sensory fibres enter and motor fibres leave at every segment, while the through traffic runs on the outside. Those local circuits are enough for reflexes: in the knee jerk a stretch receptor's fibre excites the motor neuron of the same muscle directly in the front horn, and the leg kicks with no part played by the brain.