How do chemicals work in the brain?
The brain is a
complex organ that is comprised of gray matter and white matter. Gray
matter consists of the cell bodies of neurons and other support cells,
and the white matter consists of long tracts of axons that run between
the neurons. Different areas of the brain have somewhat specific
functions. For example, the motor cortex controls voluntary movements of
the body, and the sensory cortex processes information to the senses.
Different areas of the brain communicate with other areas nearby as well
as more distantly. Information travels via the axons of the neurons
within the white matter areas of the brain.
The brain contains billions of neurons, which interact with each other
electrochemically. This means that when a nerve is stimulated, a series
of chemical events occur that in turn create an electrical impulse. The
resulting impulse propagates down the nerve length known as the axon and
causes a release of chemicals called neurotransmitters into a space
between the stimulated nerve and the nerve that it wishes to communicate
with, known as the synaptic cleft. The neurotransmitters interact with
receptors on the second nerve, either stimulating or inhibiting them. The
interaction between the neurotransmitters and receptors can be likened to
a key interacting with a lock where the neurotransmitter or "key" engages
the receptor or "lock," causing it to "open." This opening is really a
series of chemical changes within the second nerve that either causes
that nerve to "fire" or "not fire." Thus, brain activity is the result of
an orchestrated series of nerves firing or not firing in a binary
fashion. In that sense, it is much like a computer where very complicated
processes begin their lives as a series of 1s or 0s (on or off, fire or
do not fire).
After the nerve fires, thereby releasing neurotransmitters into the
synaptic cleft, the neurotransmitters must be removed from the area in
order to turn the signal off. There are two ways that these chemicals can
be removed in order to turn the signal off. The first is by destroying
the chemical through the use of another chemical known as an enzyme with
that specific purpose in mind. The second is by pumping the chemical back
into the nerve that released it by using another special chemical known
as a transporter or transport pump. The process of pumping chemicals back
into the nerve is known as reuptake. It is important to understand these
basic principals of neurophysiology because all psychoactive compounds,
whether neurotransmitters, hormones, medications, or addictive drugs,
involve one or more of these simple mechanisms.
