Shoulder to elbow
Squeeze your upper arm gently. Under the muscle, you can feel a long, hard bone. That's your humerus.
It's the longest bone in your arm. It goes from your shoulder all the way down to your elbow.
Its top end is a round ball. The ball fits into a shallow socket on your shoulder blade. That makes a ball and socket joint, which lets your arm swing in circles.
The funny bone isn't a bone
Have you ever bumped your elbow and felt a zing of pins and needles, all the way to your little finger? People call that hitting your funny bone.
But it isn't a bone at all! It's a nerve, called the ulnar nerve. A nerve is like a cable that carries messages. At the back of your elbow, it runs in a groove near the bottom of your humerus, with only skin on top.
When you bump it, the nerve gets squished and sends a buzzy message. It feels strange, but it goes away in a minute or so.
Why is it called funny? Maybe because the bone's name, humerus, sounds like humorous, which means funny. It's a bone joke!
Muscles that pull
Big muscles wrap around your humerus. Your biceps, on the front, bends your elbow. Your triceps, on the back, straightens it.
Your deltoid, the round muscle on top of your shoulder, holds on to the humerus and lifts your arm out to the side.
Try it: make a muscle by bending your arm. Feel your biceps bunch up on the front of your humerus.
The elbow end
The bottom of your humerus is wide, with a bump on each side. You can feel both bumps at your elbow. The funny bone nerve runs behind the inside one, the bump nearer your body.
Here, the humerus meets your two forearm bones to make your elbow. The elbow is a hinge, like a door, so it bends one way.