L 8 & 9 | Neurobiology of stress Flashcards
(16 cards)
Organization of the Central Stress Regulatory Network: Detection, Generation, Regulation, & Termination
The central stress regulatory network is composed of key brain regions, neural circuits, and endocrine pathways involved in detecting, generating, regulating, and terminating the stress response:
Detection: Stress detection begins with the amygdala, which assesses emotional and psychological threats, and the brainstem for physical stress (e.g., changes in blood pressure). The hypothalamus integrates these signals.
Generation: The stress response is generated by the HPA axis and SAM axis. The HPA axis triggers cortisol release, while the SAM axis rapidly increases adrenaline for immediate action.
Regulation: Higher brain areas like the prefrontal cortex and hippocampus regulate the intensity of the stress response, helping adjust reactions based on the context (e.g., is the threat real or perceived?).
Termination: Cortisol binds to glucocorticoid receptors (GRs) in the hypothalamus and pituitary, inhibiting the release of CRH and ACTH, which shuts down the stress response via negative feedback
Afferent vs. Efferent Circuits
Afferent circuits carry information from the body to the brain, such as signals related to physiological stress (e.g., blood pressure, pain). These signals pass through structures like the brainstem, specifically the nucleus of the solitary tract (NTS).
Efferent circuits transmit signals from the brain to the body, activating responses like increased heart rate or cortisol release via pathways like the sympathetic nervous system or the HPA axis
Direct vs. Indirect Pathways
Direct pathways involve immediate, rapid responses. For example, the SAM axis directly activates the adrenal medulla to release adrenaline and noradrenaline within seconds in response to stress.
Indirect pathways are slower and involve hormonal cascades. The HPA axis is an example: the hypothalamus releases CRH, stimulating the pituitary to release ACTH, which then triggers the adrenal cortex to release cortisol. This process can take minutes to fully unfold
Global Neural Regulation of Endocrine & Autonomic Stress Response
The HPA axis governs the endocrine response to stress by regulating cortisol levels. Cortisol modulates various systems like immune function and metabolism.
The SAM axis controls the autonomic stress response, especially through the sympathetic nervous system, which rapidly increases heart rate, blood pressure, and energy mobilization.
Both systems are integrated by brain regions such as the hypothalamus, amygdala, and prefrontal cortex. These regions help coordinate the body’s response based on the nature of the stressor
Physical vs. Psychological Stressor Networks & Consequences
Physical stressors (e.g., temperature changes or physical injury) are detected via interoceptive circuits. These are processed by the brainstem and hypothalamus, leading to rapid autonomic responses such as elevated heart rate or increased blood pressure.
Psychological stressors (e.g., social evaluation) activate higher brain areas, such as the prefrontal cortex and amygdala, which indirectly modulate the HPA and SAM axes. Psychological stress often leads to a broader array of responses, affecting both cognition and emotions.
Consequences: Physical stressors elicit more direct physiological responses, while psychological stressors involve complex emotional and cognitive processes, which can exacerbate allostatic load—the wear and tear on the body due to chronic stress
Interoceptive vs. Exteroceptive Sensory Systems
Interoceptive systems detect internal bodily states, such as blood pressure or hunger, and relay information via visceral afferents to the brainstem and hypothalamus for regulation.
Exteroceptive systems gather information from the external environment (e.g., visual, auditory, or olfactory stimuli) and transmit it to higher brain regions like the amygdala and sensory cortices, playing a critical role in detecting external threats
Survival vs. Defense Circuits
Survival circuits involve reflexive, automatic responses to physical threats, largely managed by the brainstem and hypothalamus.
Defense circuits, however, involve higher-level processing in the amygdala and prefrontal cortex, preparing the body to cope with threats like social rejection or fear
Detection & Integration of Physical Stressors (Blood Pressure Example)
Physical stressors such as high blood pressure are detected by baroreceptors in the blood vessels. These sensors send signals to the brainstem, particularly the NTS, which integrates the information and triggers compensatory responses, such as adjusting heart rate and blood vessel constriction to maintain stability
Circuit for Detection of Psychological Stressors
Unconscious processing of psychological stressors occurs in the amygdala, which triggers a rapid stress response before conscious awareness.
Conscious processing involves the prefrontal cortex, which evaluates the threat and modulates the stress response accordingly. These processes influence the activation of the HPA and SAM axes, leading to a coordinated physical and emotional response
Role of the Amygdala
The amygdala is the brain’s primary center for detecting emotional threats. It integrates sensory information related to fear or anxiety and triggers stress responses by activating the HPA axis and the SAM axis, leading to cortisol and adrenaline release
Role of the Limbic System in Stress Regulation
The limbic system, including the amygdala and hippocampus, plays a major role in emotional regulation and memory. It helps modulate stress responses by interacting with the prefrontal cortex and hypothalamus, integrating emotional, cognitive, and physiological reactions
Negative Feedback Loops in Stress Termination
The HPA axis is terminated through negative feedback loops where high cortisol levels signal the hypothalamus and pituitary to stop releasing CRH and ACTH, respectively. This shuts down the further release of cortisol, preventing excessive stress hormone production and helping return the body to baseline
Reflective vs. Reactive Functions
Reflective functions involve higher-level decision-making, typically mediated by the prefrontal cortex, and allow for adaptive responses to complex stressors.
Reactive functions are automatic and rapid, involving the brainstem and amygdala, which trigger immediate physiological changes (e.g., fight-or-flight response
Endocannabinoid System in Stress Response
The endocannabinoid system plays a dual role in activating and terminating stress responses. It helps regulate the HPA axis and can dampen overactivity of stress pathways, aiding in recovery from stress by promoting relaxation and reducing anxiety
Neuromodulation Techniques (TMS, tDCS)
TMS (Transcranial Magnetic Stimulation): Non-invasive stimulation using magnetic fields to modulate brain activity, often targeting the prefrontal cortex to reduce stress and improve mood.
tDCS (Transcranial Direct Current Stimulation): Applies low electrical currents to the scalp to modulate cortical activity. Anodal tDCS stimulates neuronal activity, while cathodal tDCS inhibits it. Both techniques can modulate stress responses
Brain Stimulation & Stress Reactivity
Brain stimulation techniques like TMS and tDCS have been shown to alter stress reactivity, reducing negative emotions and lowering cortisol levels. They may enhance performance in stressful situations by modulating the prefrontal cortex and other related brain circuits
