Hi, bel - as no-one else is answering (perhaps they have understood and I have misunderstood, that your question was rhetorical?? no matter, I wil press on anyway!) may I offer a word of explication.

Your "funny-bone" is the bone which runs from shoulder to elbow - effectively keeping the two joints apart. It is the end of this bone which you knock so painfully. Its anatomical name is humerus which has been jocularly translated into "funny bone", fairly obviously, I guess.
Dr Bill is stretching the term even further by suggesting that this "humerus" bone is the seat of one's appreciation of "humour".
[/didacticism]