Biological Effects - RF/Microwave Interaction with Biological Tissues - page 96

organs. They are distinguished by the anatomic distribution of their nerve
fibers. One major difference between them is of prime interest in biomi-
crowaves: The postganglionic fibers secrete different neurohormones. The
parasympathetic system secretes substances such as acetylcholine from fibers
termed “cholinergic,” while the sympathetic system secretes epinephrine and
adrenaline from fibers termed “adrenergic.”
Many of the functions of the autonomic system are regulated by the hypo-
thalamus , located in the brain between the cerebrum and the midbrain. The
hypothalamus affects the cardiovascular system, body temperature, appetite,
and the endocrine system, among its many functions. Body temperature and
endocrine functions are under direct influence of EM fields.
The nerve impulses pass to or come from the brain via 12 pairs of cranial
nerves or via the spinal cord. Some cranial nerves, such as the optic nerve, are
sensory nerves interfacing with sense organs. Others, like the facial nerve, are
motor nerves, connecting to muscles and glands. Interneurons carry impulses
between the sensory and motor nerves.
In the CNS, the spinal cord , which is continuous with the brain, is the center
for spinal reflexes and is also a two-way communication system between the
brain and the body. From an electrical engineering point of view, it is inter-
esting to wonder about the equivalent electrical parameters of such a system.
The neuroglial cells are within the tissues of the brain and spinal cord. They
fill in the space and support the neurons by a process known as scaffolding.
Unlike neurons, neuroglial cells can reproduce.
If the EM fields are active in altering the activity and function of the CNS,
then one may expect to see those changes reflected in the concentrations of
neurotransmitters in various regions of the brain [33]. Hence, total or local
exposure to EM fields at levels and frequencies where the CNS could be influ-
enced will yield changes in neurotransmitter concentrations. It has been shown
that the excitation of acupuncture points by microwaves (from 0.2 to 3 GHz)
may produce an efficient analgesic effect, as shown by the corresponding
increase in the pain threshold, measured by a dolormeter [34]. Furthermore,
respective variations in pain threshold and neurotransmitter release in the
center of pain reception in the brain are proportional [35].
Data about the effects of microwaves form a heterogeneous ensemble of
facts that are not readily classified in terms of thermal versus nonthermal
interactions [13]. The first category includes interactions with the peripheral
nervous system and certain neurovegetative functions, alterations in EEG,
changes in animal behavior and, possibly, the permeability of the blood-brain
barrier (BBB). The second category could include membrane interactions that
affect the ion fluxes, the modulation of neuronal impulse activity, and, possi-
bly, induced arrhythmia in isolated hearts. Also included in this category could
be the somewhat confused collection of dystonias and behavioral effects that
are often referred to as the microwave syndrome. (See Sections 3.2.5 and
3.5.1.) It is also possible that there are some subtle very low-level effects of
microthermal or nonthermal origin, which are masked by the more apparent