Page 146 - The Cell in 40 Topics

hen you run into friends in the street who call out, “Hello!”
the sound waves they emit are collected by your ear. At sea
level, sound travels through 6 meters (19 feet) of air in 1/50 second.
The air vibrating in both of your ears travels the short distance to your
middle ear at great speed. The ear membrane, only 7.6 millimeters (0.2
inches) in diameter, begins vibrating, which vibrations are transmitted to
three small bones that convert these sound vibrations into mechanical vi-
brations. The vibrations in these bones are then transmitted to the inner ear
and the fluid inside a structure known as the cochlea, which resembles a
snail (Figure 111).
Inside the cochlea, which contains fine strands of varying thicknesses,
just like the strings of a harp (Figure 112), different tones are divided from
one another. Your friend’s voice literally plays these strings. First the thick-
est strands vibrate, followed by the thinner ones. Finally, tens of thousands
of rod-shaped bodies in the inner ear activate the hearing nerves through
their own vibrations (Figure 113).
The sound of your friends’ “Hello” is now an electrical signal that

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