The Human Nervous System

Touch something scalding and your arm is already moving before you have decided anything. You did not choose it, you could not have stopped it, and the pain arrives afterwards like a report filed late. That tiny gap between the injury and the feeling is the most revealing thing your body does all day, because it shows that a decision was taken somewhere other than in your thoughts.

This lesson follows a single signal from the skin of a fingertip to the muscle that pulls the hand clear. You will meet the three kinds of neurone and learn which direction each one carries traffic, see what actually crosses the tiny gap between one nerve cell and the next, take apart a pain-withdrawal reflex step by step, and finish by measuring a reaction time and judging whether the measurement can be trusted. By the end you will be able to take any piece of behaviour an examiner puts in front of you, however unfamiliar the animal or the situation, and lay it out as stimulus, receptor, coordinator, effector, response.