Page 62 - The Miracle of Electricity in the Body

60 THE MIRACLE OF ELECTRICITY IN THE BODY

it seems as if the muscles contract as soon as the thought occurs to us.
The reason our movements follow our perceptions so quickly, without
our expending a conscious effort, is that nerve transmission takes place
37
at speeds of up to 354 kilometers (220 miles) an hour. In the 1-meter-
long (3.3-foot) sciatic nerve in the legs, that speed rises to 467 kilometers
(290 miles) per hour. 38
In some situation, the timing of signals reaches extraordinary pre-
cision. For us to make a distinction between B and P sounds when we
speak, our lips need to open in as briefly as 1/30,000 second before our
vocal cords move. Therefore, our listeners do not confuse the letter P
with the letter B, which emerges as a result of the simultaneous opening
of our lips and vibration of our vocal cords. In other words, we owe our
ability to distinguish between the words pat and bat to a timeframe of
just thirty thousandths of a second. This distinction is of great impor-
39
tance to our communication. But since the brain arranges this time frame
for itself, there is no need for you to think about it. When the signal for
the vocalization of P or B occurs, all these events take place in sequence,
one after the other.
To better understand the significance of the myelin sheath, consider
Multiple Sclerosis (MS). In this disease, the protective sheath around the
nerves that carry messages in the brain and spinal column is damaged
in places, and there appears hardened tissue known as sclerosis. These
hardened tissues may occur in many sites throughout the nervous sys-
tem and—by preventing the transmission of signals along the nerves
and interfering with communication between the brain and other or-
gans— lead to a wide variety of defects. In the same way that holes may
damage the insulation around electrical cables, gaps can also appear in
the defective myelin sheath, which interferes with the transmission of
messages.
When you remove one of the standing dominoes in the line, the
consecutive falling of the line is interrupted when the sequence reaches

this gap. In the same way, a damaged myelin sheath causes an interrup-
tion in the transmission of nerve signals. The effect of one missing domi-
no can be compared to that of serious neural or spinal damage. Nerve