Curiosity 3 of 10
3. The smallest bone in the body is inside the ear
The stapes, a tiny bone of the middle ear, measures about 3 millimeters and is the smallest bone in the human body. Together with two neighboring bones, it carries sound from the eardrum into the inner ear.
A chain of three tiny bones
Sound reaches the ear as air vibration and makes the eardrum vibrate. Behind it there are three ossicles in sequence: the malleus, the incus and the stapes, names that come from the shape of each one.
They work like a small lever. The vibration passes from one to the next and reaches the stapes, which pushes a membrane at the entrance of the inner ear, which is filled with fluid. There, sensory cells turn the movement into signals for the brain.
This chain also concentrates the force of sound. Since the eardrum is much larger than the base of the stapes, the vibration is concentrated over a small area, which helps pass the sound from the air into the fluid of the inner ear without losing it along the way.
The ossicles are among the few bones that are already almost adult-sized at birth. The largest bone in the body is the femur, the thigh bone, which alone corresponds to about a quarter of a person's height.
Did you know? Attached to the stapes is a tiny muscle, the stapedius, one of the smallest in the body. In the presence of very loud sounds, it contracts and reduces the vibration that reaches the inner ear.
