Last updated: Fri, Jul 26, 2024
Scratching is a reflex, at least for dogs. It consists of two components, a scratching motion and a sense of position. In the sometimes macabre world of physiological research, a “spinal” animal is a live animal whose brain has been detached from his or her spine.
The position sense of the scratch reflex is a highly developed function. If a flea is crawling as far forward as the shoulder of a spinal animal, the hind paw can still find its position, even though 19 muscles in the limb must be contracted simultaneously in a precise pattern to bring the paw to the position of the crawling flea. To make the reflex even more complicated, when the flea crosses the midline, the first paw stops scratching and the opposite paw begins the to-and-fro motion and eventually finds the flea.1
If you have been wondering how scientists learned some of the things they know, this is a clue.