# Transcript

The HPA axis consists of two brain structures, the hypothalamus and the pituitary, and an area outside the brain, the adrenal cortex, which is part of the adrenal gland that sits atop each of our kidneys. The HPA axis has important links to other parts of the brain, such as the amygdala, the hippocampus and the prefrontal cortex.

Communication between the different structures is shown by connecting arrows or lines, and by the direction of travel of chemical messengers such as CRF from the amygdala and hypothalamus, ACTH from the pituitary, and cortisol from the adrenal cortex. Cortisol is released into the bloodstream, and its breakdown by enzymes in the blood is shown as a fading-out of the cortisol molecules. Action potentials travel from the hippocampus and prefrontal cortex to the hypothalamus.

Signals are received by receptors, shown as solid semicircles, on the different brain structures. Signals to some receptors are stimulatory, as shown by radiating red lines. The more red lines generated, the stronger the stimulation. Signals to other receptors are inhibitory, as shown by the blue lines. The more blue lines generated, the greater the inhibition. Of particular interest in this animation are the black receptors, which are glucocorticoid receptors. These are the receptors to which cortisol attaches. The grey semicircles represent non-glucocorticoid receptors.