HPA Stress Response

Question 1

What are the two main components of the stress response?

Answer 1

• Fast Response: Sympathetic-Adreno-Medullar (SAM) Axis
• Slow Response: Hypothalamic-Pituitary-Adrenal (HPA) Axis

Question 2

Describe the fast stress response (SAM Axis)

Answer 2

Sympathetic-Adreno-Medullary (SAM) axis
• Immediate (seconds to minutes)
• “Alarm” Stage – immediate short-term crisis response
• Releases norepinephrine and epinephrine from adrenal medulla
• Prepares body for “fight or flight”

Question 3

Describe the slow stress response (HPA Axis)

Answer 3

Hypothalamic-Pituitary-Adrenal (HPA) axis
• Sustained (peaks ~20 min post-stressor)
• Releases glucocorticoids (e.g., cortisol)
• Supports prolonged escape/defence

Question 4

What are the key structures and hormones in the HPA axis?

Answer 4

1. Hypothalamus (PVN): Releases CRH (corticotropin-releasing hormone)
2. Anterior Pituitary: Releases ACTH (adrenocorticotropic hormone)
3. Adrenal Cortex: Releases glucocorticoids (cortisol in humans, corticosterone in rodents)

Question 5

How is the HPA axis shut down after stress?

Answer 5

Negative feedback loop:
• Glucocorticoids bind to receptors in the hippocampus, cortex, and hypothalamus
• Inhibits CRH and ACTH release
• Reduces glucocorticoid production

Hippocampus plays a key role by inhibiting the PVN of the hypothalamus

Question 6

How does stress affect memory and learning?

Answer 6

• Moderate stress enhances memory consolidation (primarily emotional)
• Stress hormones (e.g., cortisol, norepinephrine) enhance attention and encoding
• High stress impairs memory (inverted U-shaped curve)

Question 7

What role does norepinephrine play in memory?

Answer 7

• Enhances memory consolidation via β-adrenergic receptors in the amygdala
• Blocking NE (e.g., with propranolol) impairs consolidation of emotional events

Question 8

What evidence supports the role of norepinephrine and the amygdala in emotional memory?

Answer 8

• Hatfield & McGaugh (1999): NE in BLA improved memory in rats; propranolol impaired it
• Cahill et al. (1996): Amygdala activity during emotional film viewing predicted later recall
• Van Stegeren et al. (2005): Propranolol reduced amygdala activation to moderately aversive images