The instrumentation developed to detect chemical contamination is an
extension of our human senses. One of these senses, the sense of smell,
occurs primarily because chemicals volatilize. This volatilization occurs most
readily at room temperature for generally light molecules. These molecules
float through the air, and, upon entering nasal passages behind the nose,
activate olfactory sensor neurons. The neuron activation occurs as the odorant
molecule binds to the neuron’s cilia. In order for the odorant to bind and
ultimately be recognized, the receiving neuron must have been encoded by a
specific gene to recognize a particular chemical structure.
Signals from neurons with the same receptors converge on glomeruli in the
olfactory bulb located in the brain. The glomeruli’s response then creates
a code that is transmitted by nerve fibers to various brain regions. This
transmission means that smell is interpreted both from a sensory perspective
and as an initiator of memory, emotions, and behavior in the limbic system.
These signals also affect the brain’s cortex where conscious thought occurs.
Now to the really interesting stuff: Genes also appear to control other
types of chemical sensing, such as the ability of sperm to locate an egg.
Similar receptors may function in a special structure in the nose called the
vomeronasal organ. The vomeronasal organ detects pheromones. These
signals may then regulate hormone release, mating, and social functions in
animals, including humans. The chemicals responsible for these biological
processes are not the typical volatiles!
Over the course of time, these systems have protected us from rotten food,
poisons, enemies, animal attack, and other “stinky” humans. Unfortunately,
in our modern environment many chemicals never experienced by even
our recent ancestors are used. To make matters even more complicated,
these chemicals may change over time with exposure to our very dynamic
ecosystem, including other contaminants; making their detection more
difficult. Thus, instrumentation to detect environmental signals was and is
needed, given the limitations of the human sensory system.