Final answer:
The HPA axis is under excitatory control of the amygdala and inhibitory control of the hippocampus. The amygdala stimulates the sympathetic fight-or-flight response in the hypothalamus, while the hippocampus can inhibit the HPA axis activity.
Step-by-step explanation:
In the hypothalamus, the HPA axis is under excitatory control of the amygdala and the inhibitory control of the hippocampus.
The amygdala, located in the limbic lobe, plays a role in emotional responses and projects signals to the hypothalamus via the medial forebrain bundle. When you are anxious or scared, the amygdala stimulates the sympathetic fight-or-flight response in the hypothalamus.
On the other hand, the hippocampus, also part of the limbic system, regulates memory and emotion. It can inhibit the activity of the HPA axis by modulating hypothalamic CRH release and autonomic centers in the brainstem.