I hear the music on the radio.
The radio speakers disturb the molecules of air in an outgoing pattern, and soon the disturbed air reaches me. When I am in its path, the molecules of air push against my tympanic membrane, the ear drum, back and forth. On the other side of the tympanic membrane those three smallest bones, whimsically shaped like a hammer, anvil, and stirrup, fit together in an intricate interlocking shape. They gently tap, tap, tap at the membrane on the other side of the middle ear leading to the inner ear, the eliptical window, one of the two little windows of the cochlea. The other window, the oval window, gives enough flexibility to allow the fluid inside the cochlea to move.
To the north of the inner ear there are three hoop-like structures, the semicircular canals, that regulate my balance. Inside that section are otoliths, tiny crystals, that fall onto a floor spiked with nerves that feed directional information to my brain. In the brain the nerves for balance run close to the areas regulating nausea, which is why I sometimes feel sick if my position has been manipulated on the tilt-a-whirl at the carnival.
The south side of the inner ear is spun like a snail shell, around, around, larger to smaller, the cochlea. It's filled with a viscous fluid that flows gently over the cochlear membrane. If you could unwind the cochlea you might better see in your mind's eye the plush carpet of nerves spread along the structure. The ends of the nerves look like little hairs embedded into the fluid. The cochlear fluid moves very particularly according to how the little bones tap tapped on the window, stimulating precise hair cells of the cochlear membrane and causing those, and only those, neurons to fire. The neuronal signals travel into the region of the brain under the skull just on the other side of the ear: the temporal lobe. The brain interprets the firing of the nerves, digital to analog, and sends those signals on to the brain's processing centers, and so on, and so forth.
And so, I hear the music on the radio. I know it, and I smile.
12 hours ago