CHEMISTRY OF THE BRAIN: MOLECULES, MOOD, AND MENTAL ILLNESS - Chemistry: Notable Research and Discoveries - page 81

junctions play a vital role in certain networks, but they will not be dis-
cussed in detail in this chapter.
Straight-through transmission via gap junctions has the advantage
of simplicity over the complicated process of chemical transmission. But
chemical transmission gives nervous systems a great deal of flexibility.
With more links in the chain, brains have more opportunities to make
adjustments—there are more “knobs” and “controls” with which to fine-
tune the activities of neurons. Current theories of learning and memory
identify the plasticity—adjustability—of synapses as the mechanism by
which brains acquire and store information. Intelligence evolves from the
continual tweaking of chemical transmission in the brain.
But chemical transmission also makes it difficult for researchers to
study neurochemistry—the brain's chemistry. Synaptic transmission
is brief and occurs within a small portion of the protected confines of
the brain. No wonder Thoulet, Vauquelin, Courbe, and other early re-
searchers had such trouble.
MEASurIngTHEBrAIn'SCHEMICAlS
Studying the chemistry and biology of brain function often requires
the researcher to find a model organism—an organism that has ana-
tomical or chemical features conducive to study. Loewi, for example,
studied chemical transmission in the vagus nerve of frogs. For axons
and synapses, many researchers have used the squid, which contains a
giant axon with a diameter of up to 0.04 inches (0.1 cm); this may seem
small, but it is about 50 times bigger than typical axons. (This particular
axon has such a large diameter because its great size helps to speed con-
duction of the impulse, which in this case carries information to help
the animal escape a predator—an action that needs to be done with as
much dispatch as the animal can muster.) The associated synapses are
also large. The British scientists Sir Alan Hodgkin (1914-98) and Sir
Andrew Huxley (1917- ) discovered a great deal of information on
ion channels in the 1940s and 1950s using this model organism.
Fundamental principles of chemistry also apply to biochemistry—bi-
ological chemistry—and the techniques of neurochemistry have improved
since the days of Courbe and his phosphorus analysis. As described in
chapters 1 and 2, chemical elements combine in chemical reactions to
form compounds. In order for chemical reactions to occur, the reac-
tants—the atoms or molecules participating in the reaction—must meet.