A few more aspects of pain pathways can lead to chronic pain or effects of chronic pain. Axons of the spinal cells that receive pain signals branch out through the CNS where they perform different actions. Some actions are important to understanding pain:
· Some branches go to the brain stem located between the spinal cord and the brain (also called the cerebrum). Nuclei in the brain stem regulate sleep and wakefulness. Input to these regions arouses you and can prevent you from sleeping. Loss of sleep can be a major problem for people with chronic pain.
· The brain stem is a major player in controlling your muscular tone and coordinating reflexes that contribute to all your movements. For example, the brain stem coordinates your withdrawal from a painful stimulus in a way that prevents you from falling over. It also governs your reflexes and can inhibit them; for example, it keeps withdrawal reflexes from going off time and time again if the pain doesn’t stop. Unlike the alarm on a timer, which doesn’t stop until someone turns it off, your brain is smart and turns the withdrawal reflex off after awhile.
· The brain stem inhibits reflexes with axons in pathways that descend to your spinal cord. There is some spillover of inhibition to spinothalamic cells in the spinal cord. Therefore, some scientists think the brain stem may play a role in regulating pain.
· Systems within the brain regulate stress reactions. One form of stress, called psychological stress, activates both the hypothalamus and the pituitary gland, which in turn leads to activation of the sympathetic nervous system. The result can be increased pain.