Dogs are nice. Some dogs are super nice, which is why we like to pet them. Ever scratch a dog and then their leg goes absolutely nuts, though? It’s just this kind of accepted facet of dog behavior that we’ve just all agreed is totally normal and don’t question at this point. Which is why we’re asking why, because we are the friend at the bar who starts a whole new conversation over some random thought. Anyway, why do dogs kick when you scratch them?
How Does it Work?
We have a decent idea of what makes the scratch reflex work thanks to a guy named Charles Scott Shellington. He’s actually the reason we have the term “synapse” (the space in which two neurons exchange information). In regards to dogs though, Shellington focused a lot on the nerves in the spine as well as reflexes. His research led him to mapping the nerves connected to motor control and the spine, basically he was trying to figure out what muscles and stuff connected to the spinal cord.
So Shellington was pretty interested in reflexes. If you’re wondering why it’s connected to your spine, you can think about when you put your hand on a hot surface. Normally, you take your hand off the thing before you actually register that you’re being burned. That’s because when the “cells are being damaged” signal gets to your spine, your hand is ordered to move before the signal gets to your brain. You might be a little annoyed that your free will is being subjugated by your spine, but try convincing your spinal cord keeping your hand on the stove is a good idea.
Anyway, Shellington published The Integrative Action of the Nervous System, and when discussing the scratch reflex, he separates the reflex into four stages. Latency, warm-up, after discharge, and fatigue.
Latency is what it sounds like, it’s the time between you scratching your dog and their leg beginning to move. Warm-up governs your dog’s leg kicking faster, and the after discharge is the phase in which your dog sometimes will continue to kick their leg around even if you stop scratching them. It’s just the other end of latency.
Does Your Dog Like It Though?
At the end of the day what we really care about is whether or not our furry friends actually like having their legs freak out or not. Your dog has some nerve bundles that when scratched have them kicking around–you probably know these nerves probably reside somewhere around their bellies.
It turns out your dog is scratching because they’re itchy. Dogs more prone to allergies are more susceptible to the scratch reflex. The scratch reflex itself is an anti-itch thing. When irritants get on your dog, like fleas, then kicking off the fleas will probably get rid of them. It would explain why “the spot” is normally around where your dog’s leg will reach, or in places that are normally unprotected (like their bellies).
So your dog might just think you scratching them on the belly is just some like… pollen or something. But on the bright side, if your dog was getting annoyed they’d probably just leave and not let you scratch their bellies.
It’s important to make sure you know your dogs when they’re young and also old, so go make sure you do here.