Cochlea a protein motor called prestin on their outer membranes; it generates additional movement that couples back to the fluid–membrane wave. This "active amplifier" is essential in the ear's ability to amplify weak sounds. The active amplifier also leads to the phenomenon of soundwave vibrations being emitted from the cochlea back into the ear canal through the middle ear (otoacoustic emissions). Otoacoustic emissions are due to a wave exiting the cochlea via the oval window, and propagating back through the middle ear to the eardrum, and out the ear canal, where it can be picked up by a microphone. Otoacoustic emissions
Stirrup did not have stirrups. It is speculated that stirrups may have been used in China as early as the Han dynasty (206 BC–220 AD); however, verified archaeological evidence of stirrups in this period is scant. Stirrups were used in China at the very latest by the early 4th century AD. A funerary figurine depicting a stirrup dated AD 302 was unearthed from a Western Jin dynasty tomb near Changsha. The stirrup depicted is a mounting stirrup, only placed on one side of the horse, and too short for riding. The earliest reliable representation of a full-length, double-sided riding stirrup was