Yeah, it has nothing to do with deadening nerves. Maki wara boards are solid hard, itll toughen up your knucks great... and youll end up with debilitating nerve damage and arthritis. You see an old school karateka whos been slamming makiwara all his life, they cant hold soup in a spoon.
anyways, the nerves do not 'deaden', they appear to recede into the skin because the skin itself becomes thicker. bone density increases with striking, but not by calcification, which occurs to mend fractures, fractures will not help u they degrade the structural integrity of the bone regardless of calcification.
best is to hit wallbags of gravel, rubbing hands afterwards with dat dit jow or woodlock is good for circulation... good the blood carries the oxygen and building blocks required to heal yourself correctly so it is highly recommended to use this after conditioning hands... and lots of deep rubbing.