brain, spinal cord, and nerve disorders
Brain
Introduction
The brain’s functions are both mysterious and remarkable, relying on billions of nerve cells and the internal communication between them. All thoughts, beliefs, memories, behaviors, and moods arise within the brain. The brain is the site of thought and intelligence, and the control center for the entire body. The brain coordinates the abilities to move, touch, smell, taste, hear, and see. It enables people to form words, speak, and communicate, understand and manipulate numbers, compose and appreciate music, recognize and understand geometric shapes, plan ahead, and even to imagine and fantasize. The brain reviews all stimuli—from the internal organs, surface of the body, eyes, ears, nose, and mouth. It then reacts to these stimuli by regulating the following: Position of the body Movement of limbs Rate at which the internal organs function Mood Consciousness None The brain consists of the cerebrum, brain stem, and cerebellum. Each half (hemisphere) of the cerebrum is divided into lobes. No computer has yet come close to matching the capabilities of the human brain. However, this sophistication comes with a price. The brain needs constant nourishment. It demands an extremely large amount and continuous flow of blood and oxygen—about 25% of the blood flow from the heart. The overall energy consumption of the brain does not change much over time, but certain areas of the brain use more energy during periods of increased activity (for example, when attempting to learn a new language or learning a new task such as ice skating). A loss of blood flow to the brain for more than about 10 seconds can cause a loss of consciousness. Lack of oxygen or abnormally low sugar (glucose) levels in the blood can result in less energy for the brain and can seriously injure the brain within 4 minutes. However, the brain is defended by several mechanisms that can work to prevent these problems. For example, if blood flow to the brain decreases, the brain immediately signals the heart to beat faster and more forcefully, and thus to pump more blood. If the sugar level in the blood becomes too low, the brain signals the Overview of the Adrenal Glands to release The brain rarely produces new nerve cells (neurons) but can make new support cells (glial cells) throughout life. No computer has yet come close to matching what the human brain can do. About 25% of the blood pumped by the heart goes to the brain. also protects the brain. It is made up of cells that line blood vessels of the brain. These cells allow some substances to reach the brain and block others. The blood-brain barrier is necessary because in the brain, unlike in most of the body, the cells that form the capillary walls are tightly sealed, for example, to protect it from harm caused by toxins and infections. ( Capillaries , the smallest of the body’s blood vessels, are where the exchange of nutrients and oxygen between the blood and tissues occurs.) Because the blood-brain barrier controls substances that can enter the brain, penicillin, many chemotherapy drugs, some toxic substances, and most proteins cannot pass into the brain. On the other hand, substances such as alcohol, The activity of the brain results from electrical impulses generated by nerve cells (neurons), which process and store information. The impulses pass along the nerve fibers within the brain. How much and what type of brain activity occurs and where in the brain it is initiated depend on a person’s level of consciousness and on the specific activity that the person is doing. The brain has 3 main parts: Cerebrum Brain stem Cerebellum Each part (cerebrum, brain stem, and cerebellum) has a number of smaller areas, each with specific functions. 