The fight or flight response flow diagram is shown here:
So in the flow diagram, you see that fear or anxiety can activate the amygdala. The amygdala in turn activates the sympathetic nervous system via the locus coeruleus, and the amygdala also activates the hypothalamic pituitary adrenal axis (HPA axis).
With the activation of the sympathetic nervous system, it activates smooth muscles and glands directly via nerves. The sympathetic nervous system also activates the adrenal medulla to release adrenaline into the bloodstream.
With the activation of the HPA axis, the hypothalamus releases corticotropin releasing factor (CRF), which reaches the pituitary and ACTH is released. The ACTH reaches the adrenal cortex, and triggers the release of cortisol into the bloodstream.
So the activation of the sympathetic nervous system leads to activation of smooth muscles and glands directly, and the release of adrenaline from the adrenal medulla. And the activation of the HPA axis leads to the release of cortisol from the adrenal cortex. So all of this then leads to the physical symptoms of anxiety that is seen in the fight or flight response.
