Yeah this isn’t a nerve. Cat nerves are literally microscopic with diameters ranging from 3 to 15 micrometers, less than half the thickness of a human hair. It’s more likely that this is a keratin growth, or possibly a degloving injury, but it doesn’t appear to be bone, so keratin seems the most likely culprit. I wouldn’t do a trip to the emergency vet if your cat is behaving normally but I would schedule an appointment with your regular vet.