Stressful experiences activate components of the limbic system, which includes the hypothalamus, the hippocampus, the amygdala, and other nearby areas. In response to neurosensory signals, the hypothalamus secretes corticotrophin-releasing factor (CRF) and arginine vasopressin (AVP), both of which activate the pituitary to produce hormones such as adrenocorticotropic hormone (ACTH). Circulating ACTH stimulates the production of glucocorticoids from the adrenal cortex. The sympathetic nervous system originates from the brainstem, and the pre-ganglionic neurons terminate in the ganglia near the spinal column. From these ganglia, post-ganglionic fibres run to the effector organs. The main neurotransmitter of the pre-ganglionic sympathetic fibres is acetylcholine and the typical neurotransmitter released by the post-ganglionic neurons is noradrenaline. The adrenal medulla contains chromaffin cells, which release mainly adrenaline.