Page 39 - Spring2018

AXONS AND THIMEROSAL (molecules called tubulin) are disassembled, Unfortunately,
Within the brain, nerve cells called neurons causing the axon to disintegrate. Long-range
are the basic building blocks of the nervous axons—the ones that connect different parts of in neurons
system. Neurons connect to one another, form- the brain—are especially vulnerable to these exposed to
ing a network of communication (see Figure 1). toxic exposures. toxicants such
Neurons send and receive information using Neurons have a limited capacity to regen-
tiny electrical and chemical signals, thereby erate their axons, but for many reasons (some as the mercury
allowing a person to perceive, think and un- known and some unknown) the brain loses much in thimerosal,
derstand the world. of its ability to regenerate itself early during the the structural
A typical neuron has a cell body, an axon (a developmental period. Postnatal, mature neu-
long, slender, thread-like projection that sends ronal axons can only regenerate for very short building blocks
information) and dendrites (shorter branches distances, regardless of the original length of of the axon

that receive information). Although a neuron the axon. The shorter the distance between the (molecules
may have many dendrites, it has only one axon regeneration site and its target, the more suc-
(see Figure 2). cessful the regeneration of the axon. called
Axons can vary in length from approxi- Regeneration is particularly difficult for tubulin) are
mately one millimeter to one meter. Short-range long-range axons. As the brain tries to regener- disassembled,
axons, which are required for short-range com- ate after a loss of long-range axons, the regenera-
munications within a single brain region, only tion process often results simply in an increase causing the
need to span short distances. in the number of short axons. Studies show axon to
Long-range axons are required for long- that when long-range connections decrease or disintegrate.
range neurons that aim to link distinct brain are lost, short-range connections increase. Im-
regions, and they sometimes must span long portantly, the opposite occurs in normal brain
distances. For example, a long-range axon may development. As the normal brain develops and
extend from the frontal lobe (the front part of matures over the years, its connectivity shifts
the brain) to the cerebellum in the back part of from local to more global processing—that is,
the brain. Long-range axons are predominantly from short-range to long-range connectivity.
used for sensory processing, for attention and Coincident with increased thimerosal ex-
for putting thoughts together from different posure, three neurodevelopmental disorders
areas of the brain. dramatically increased in prevalence beginning
Unfortunately, in neurons exposed to in the 1990s—ASD, ADHD and tic disorder.
toxicants such as the mercury in thimerosal, Research suggests that children who developed
the structural building blocks of the axon one of the three disorders following exposure to

FIGURE 1: Neurons interconnect to send and receive FIGURE 2: The dendrite receives information and
information. the axon sends information.

SPRING 2018 Wise Traditions 37