The abnormal reaction of the plantar reflex means what?

Test spinal cord. Normal person with intact upper ( brain nerve cell to spine ) and lower ( from spine and down ) neuron , when lateral part of sole is gently searched, big toe will flexes , normal reflex, both are intact when abscent then it is indicative of damage to upper motor neuron. Simple explanation brain cell damages it will not regenerate, when a perpheral nerve damaged it will grow back, good prognosi.