Introduction
This page is the second part of a study of articles.
An overview on stress neurobiology: Fundamental concepts and its consequences by Rumi Iqbal Doewes, Lekshmi Gangadhar and Saranyadevi Subburaj
There are many different types of stressors and our bodies and brains react to them in different ways.
Physical stressors
When faced with physical stressors, the hypothalamus and the brainstem are the brain areas that react to it.
Hypothalamus
The region below the thalamus that links the brain and the endocrine/ hormonal system.
Brainstem
An area at the bottom of the brain connected to the spinal cord.
It regulates basic activity such as breathing, heart rate and balance.
The brainstem being connected to the spinal cord, allows for a rapid physical response.
This is where the SAM axis response comes in by increasing alertness and wakefulness. In some cases, it also evaluates the situation in order to prepare for the next dangers.
The HPA axis is slower than the SAM axis. This is because the it relies on hormones which can only travel through the blood vessels.
Making it much slower than the SAM axis response by neurotransmitters.
The forebrain also analyses the physical stressors. When it detects a (potential) threat, it will activate the circuit of the paraventricular nucleus of the hypothalamus (PVN).
Paraventricular nucleus of the hypothalamus
A part of the hypothalamus, at the top, that is involved in regulating the autonomic nervous system.
This circuit is made of many neurons that send autonomic output to the brainstem and the spinal cord thus, activating the autonomic nervous system and regulating the HPA axis response.
Autonomic nervous system
The autonomic nervous system is what regulates stress, heart rate, growth, digestion, blood pressure and many other functions of our body that can’t be controlled voluntarily.
The involvement of the ANS is on point where the response to physical stressors and psychological stressors vary.
Psychological stressors
These kind of stressors are less likely to activate the ANS as a response.
This doesn’t mean the reactions are fully psychological too. Many physical responses do occur.
These reactions are mainly regulated by areas such as the amygdala, the hippocampus, the prefrontal cortex, the ventral tegmental area, the PVN and the nucleus accumbens.
Ventral Tegmental area
VTA
One of the two main regions releasing dopamine in the brain. It plays an important role in the reward system and sends dopamine to limbic and cortical regions.
Nucleus accumbens
A part of the ventral striatum involved in motivational and emotional processes. It mainly receives dopamine from the VTA.
The prefrontal cortex has various roles in stress, some inhibiting it and others promoting it. It has been seen to have functional links with the PVN but only indirect ones.
The amygdala and its role in the stress response
The amygdala, which also receives from the PFC, mainly stimulates the production and release of corticosteroids, including glucocorticoids.
Corticosteroids
A group of steroid hormones produced in the adrenal gland of vertebrates.
However, its’ subnucleis were all found to have different roles.
The basolateral nucleus ( BLA ) is important in the anticipation of stressors and the processing of psychosocial ones but doesn’t affect corticosteroid secretion.
This is why it is thought that its main function is the creation of adverse memories rather than the evaluation of stressors.
It has many links from and to the PFC which have been found to be active during short term memory recall and important for memory retention and the stress response.
The part of the amygdala that receives a lot from the BLA is the medial nucleus.
This part sends out information to the brainstem regions and the PVN regions, suggesting a stronger involvement in the stress response.
The PVN however, also outputs to the Central nucleus of the amygdala ( CeA ). These circuits are active during the recall of terrifying long term memories.
Thi nuclei is linked to the periaqueductal grey, an area involved in the threat response system.
Periaqueductal grey
A part of the brainstem that regulates pain, sympathetic responses and defensive behaviours.
Threat response system
The brains circuits that prepare and respond to a threat.
The main area is the amygdala.
This area can be divided into the dorsal part and the ventral part with the first active in response to unconditioned risks and the latter to conditioned risks. They both show different responses.
Previous part : The two stress response components
Next part : The hippocampus, genetics and molecules of stress
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