Summarized is all the material from the master course neurobiology of stress given within the neuroscience profile. Summary contains text and explaining figures. All lectures, workgroups, and self study is included.
Summary Neurobiology of stress
Biomedical Sciences Master Course
Radboud University, Nijmegen
Made by: Georgia Graat
,Every day we experience stress in varying forms and degrees. When we are exposed to potential
threats, called stressors, our brain initiates a course of actions that induces behavioral, physiological
and neuroendocrine responses. These responses prepare us to effectively cope with the stressor,
which can also become maladaptive under certain conditions or for vulnerable individuals.
Stress is something experienced by everyone, although with a different definition for everyone. The
same stressors also differ in how much and how often they stress someone. Stress is actually quite
an ill-defined concept. We know it elicits emotions, but an emotional response doesn’t necessarily
always mean there is a stress response. An emotion is a particular subjective state or feeling, a
quality of conscious awareness and a way of responding accompanied by physiological arousal.
Emotions may be positively or negatively affecting: fear/anxiety, sadness/grief, anger, hate,
frustration, love/devotion, hope, joy/happiness. There is always an emotional behavior as observable
physical changes, and an emotional response as measurable physiological biomarkers.
The stressor is always the stimulus whereas stress itself is the response to these stimuli. Stress is the
non-specific response of the body to any noxious stimulus or demand. Stress is currently defined as
any actual or potential threat to homeostasis, but this term has come to be used to both life-
threatening situations and everyday minor challenges. The problem is that stress is now almost
exclusively interpreted in terms of its negative consequences. Stress models are also often
ecologically irrelevant. The stress concept is misused due to circular reasoning: the presence of a
physiological stress response is often used as an indicator of stress itself. In that case, there would be
no difference in the magnitude of the stress response between positive, rewarding situations and
negative, aversive situations.
However, there is always a whole range of systems in play when there is an actual stress response.
These all together lead to adaptive physiological and behavioral changes in the target organs. The
presence of a physiological stress response is often only measured using cortisol amounts. Cortisol is
released when you are stressed. But these systems for stress also support other behavior and do not
automatically say the same as the stressor. The behavioral response for e.g. glucose to the muscles is
needed in many cases. So if this is the only indication, many things will be considered stressors like
fighting, sex, and exploring whereas not all are. A stressor is thus not HPA-axis or sympathetic
activation, these should only be considered as systems involved in the physiological support of any
behavior induced by any kind of intrinsic or extrinsic stimulus.
Stress responsivity is not due to the physical characteristics
of the stressor. One major important thing about stress is
that it arises due to unpredictability and uncontrollability.
The stress response is by definition the behavioral
physiological response to an uncontrollable and/or
unpredictable stimulus! The only time a stimulus is a
stressor is when it adheres to these two aspects! The stress
responsivity is thus related to the psychological appraisal of
the stressor in terms of controllability and predictability.
There are also several other things from the stressor, like
type and frequency, and the organism itself, like genetics,
endocrine responses and neurochemical responses, that
determine how well someone copes actively or passively. Repeated exposure for example leads to
more controllability and more predictability so decreases the stress response.
, Stress changes many systems in the body.
During the stress process, we know there is
mobilization of energy, cardiovascular activity
increases, improved attention (on the stressor),
better memory consolidation, suppression of
the gastro-intestinal activity, suppression of
growth, suppression of reproduction, and
suppression of the immune system. Autonomic
responses are the intrinsic part of the emotional
experience of stress. The peripheral, skeleto-
motor, and autonomic aspects severe important
functions in communication and preparation for
behavioral responses. The two main pathways
in the bodily response to stressors are the
neuroendocrine pathway of the HPA axis and
the autonomic nervous system. Homeostasis is
a biological concept important in maintaining
neutral state. The sympathetic and
adrenomedullary system play fundamental roles in deviating from this as well as returning to this
state. The hypothalamus plays one of the largest roles in correct responses, whereas the cerebral
cortex plays one of the largest roles in returning back to homeostasis through the hypothalamus.
The general adaptation syndrome came forth from this which describes the adaptive nature of the
stress response. The three stages your body goes through when exposed to any kind of stress are
alarm, resistance, and exhaustion. The alarm reaction is the first stage with the fight-or-flight
response. The sympathetic nervous system will be activated by a sudden release of hormones, and
the adrenal glands are stimulated. The resistance stage is when the body tries to repair itself after
the initial shock. To overcome stress, you need to return to homeostasis. The exhaustion stage can
come through chronic stress. It will give fatigue and burnout because enduring stressors are mentally
and physically draining.
Acute stress will always activate the fight-flight-freeze response. The adrenal medulla secretes
epinephrine and norepinephrine. The hypothalamus activates the sympathetic division of the
nervous system. The heart rate, blood pressure, and respiration increase. The blood flow to the
skeletal muscles increased. Lastly, the stomach contractions are inhibited and inflammation response
is lowered. Chronic stress, in which the person stays in the
heightened state of stress without homeostasis, can actually
be dangerous for a person. There is increased risk for
diabetes, myopathy, exhaustion, high blood pressure, major
depression, reduced growth, amenorrhea, and infectious
diseases.
The other response is from the autonomic nervous system,
with both its sympathetic and para-sympathetic division. The
sympathetic nervous system is activated due to a stressor by
the amygdala, which happens immediately as a response and
causes fast bodily changes. This is the first response because
it doesn’t need much signaling. the autonomic nervous
system activates the sympatho-adreno-medullary (SAM)
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