The Central Nervous System Quick review Spinal cord: a column of nerves that extends from the brain down the back. It transmits messages between the brain and the muscle glands in the body. Reflex: an action that is performed as an automatic response to stimulus. Stimulus: a thing or event that evokes a functional reaction in an organ or a tissue. It’s referred to as “central” because it combines information from the entire body and coordinates activity across the whole organism. ➔ The brain plays a central role in the control of most bodily functions, including awareness, movements, sensations, thoughts, speech, and memory. ➔ Some reflex movements can occur via spinal cord pathways without the participation of brain structures. The spinal cord is connected to a section of the brain called the brainstem and runs through the spinal canal. ➔ Nerve roots exit the spinal cord to both sides of the body. ➔ The spinal cord carries signals (messages) back and forth between the brain and the peripheral nerves. Many of our simple actions are reflexive. They are the way the body protects itself from harm. Have you ever wondered why you blink when you get a speck of dust in your eye? Or why some people sneeze when they sneeze pepper? These are reflexive actions designed to protect your eyes or prevent irritants from entering your lungs. Physicians sometimes test people’s reflexes to make sure their nervous systems are functioning properly.