Bernard Zalc is a neuroscientist and Emeritus Director of Research at INSERM. He led the Research Centre of the Institut du Cerveau et de la Moelle Epinière (ICM — Brain and Spinal Cord Institute) at the Pitié-Salpêtrière hospital, Paris.
Florence Rosier is a journalist specialised in science and health. Her articles frequently appear in the Science & Medicine supplement of Le Monde.

The appearance of myelin 425 million years ago marked a turning point in evolution: just as the plastic insulation on electrical wires allows the transmission of current, this membrane surrounding nerve fibres made way for a prodigious acceleration of nerve impulses in most species.
Myelin occupies nearly half the volume of the human brain and is the guarantor of our intellectual and motor performance. Without it, our thoughts and our movements would suffer overwhelming delays. We owe our reflexes to myelin: it is what makes us brake when a child dashes out onto the road, or snatch away a hand absent-mindedly placed on a burning hot stove.
When myelin is damaged, nothing works any more and there will be motor, sensory or cognitive impairments. These lesions may lead to irreversible disability.

A better understanding of the nerve impulse and its transmission leads to an improved understanding certain diseases, in particular multiple sclerosis, Guillin-Barre syndrome, Charcot disease (ALS), Niemann-Pick disease.
The first book on this wonderful invention of evolution, without which we could hardly move!