Biology Reference
In-Depth Information
showed an increase in blood pressure with age
[9]
. The lifestyle situations between
these groups naturally differed, though their entirely different psychosocial situations,
with respect to environmental stimuli, were the most obvious one.
One factor thought to be of a great importance to restore the balance of unhealthy
life style factors, such as diet and psychosocial stress, is regular physical exercise.
Extensive evidence now exists that physical activity is an important preventive tool
concerning development of cardiovascular and metabolic diseases, and sedentary
lifestyle is now generally considered to be a major risk factor for cardiovascular dis-
eases
[10,11]
. After tens-of-thousands of hunter-gatherer generations, physical activ-
ity is no longer a requirement for daily living in the 21
st
century
[12]
. Therefore, the
lack of the preventive effects of physical activity could be one important contribu-
tor, explaining some of the consequences of chronic psychosocial stress, not only on
metabolism and cardiovascular system but also on the immune system, and recent
data even suggest a protective effect of exercise on cancer
[13-15]
. One can say that
human genes and modern live-style are to some extent incongruent, as our genome
was originally selected for daily physical exertion
[12]
.
11.2 Historical Landmarks
Already Charles Darwin was struck by how closely similar emotional expressions
are in higher species, realizing that they must have been imprinted in the basal brain-
section quite early in evolution, as outlined in his topic from 1872 “
The expression
of emotion in man and animal”
[16]
. The pioneering experimental analyses of the
cerebral responses to environmental stimuli were made by three eminent physiolo-
gists, Ivan Pavlov, Walter Bradford Cannon and Walter Rudolf Hess. Their classical
studies were followed by the work of many others, including the particularly impor-
tant work of Hans Selye. From a quite different angle of approach he contributed to
the knowledge of how physical and mental noxious stimuli can via the brain induce
profound neuroendocrine changes. Selye also coined the widely used (and misused)
term “stress”
[3,17]
.
For his work, concerning the cerebral control of gastric secretion, Pavlov was
already in 1904 awarded the Nobel Prize in Physiology or Medicine to which comes
his subsequent discovery how conditioned reflexes are severely disturbed if ani-
mals are exposed to intense mental stress. Hess received the same prize in 1949 for
his experimental mapping of the brain as coordinator of a wide range of emotional
response patterns. Had Cannon not died a few years earlier, he would probably have
shared the prize with Hess for his pioneering work, covering largely all aspects of the
sympatho-adrenomedullary axis, from the highest brain centres to peripheral trans-
mitter mechanisms
[18]
. Cannon was the first to introduce the concept of homeo-
stasis and the theory that the sympathetic nervous system serves as a first line of
defence against disturbing stimuli
[1]
.
The overwhelming complexity of the brain certainly fascinated these great
physiologists - perhaps best expressed by Pavlov in his 1927 topic “Conditioned reflexes:
An investigation of the physiological activity of the cerebral cortex” (
Figure 11.2
).
