Page 176 - The Miracle of Hormones

THE MIRACLE OF HORMONES

Brain
Spinal cord

Brachial plexus
(to arm)
Thoracic nerves
(to trunk)

Lumbar plexus
Sacral plexus (to leg and pelvis)
Femoral nerve
Sciatic nerve
Because of the nerve cells
that surround the body
like a net, messages from
the brain reach the most
Tibial nerve
Common peroneal nerve remote areas of the body
with great speed. This
speed is due to the flaw-
less design of the nervous
system.

by side in a line, the line (ten microns in diameter and too small to be
seen by the naked eye) would stretch a thousand kilometers. The exis-
tence of such an extensive communication network in a brain weighing
only 1400 grams is astonishing.
Consider these figures a little more closely. Neurons are so small
that fifty average sized ones could fit on the period at the end of this sen-
tence. It is for this reason that a great amount of what we know about
62
neurons has been obtained indirectly.
When we examine the
communication extensions
on nerve cells, we see that
on every neuron there are
many dendrites that trans-
mit communication from
other neurons to the body of Myelin sheath Node of
Ranvier