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The cerebral cortex has many specialized areas that work together in ordinary thought processes. How large is the cortical area, if unfolded? The cerebral cortex, if unfolded, would have about the same surface area as a small umbrella. This is significant because it creates a large surface area for nerve cell bodies. You can see how the gray matter extends down into the fissures. What makes gray matter gray and white matter white?Ī slice of brain tissue is shown above. The axons appear white in these areas because they are coated with a fatty substance, myelin.
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It consists of communication lines: neural fibers called axons which run from the cells in the cortical layers to other parts of the brain. Other brain tissue is called white matter. Technically, gray matter refers only to cortical areas. This is called gray matter ("grey" matter in most English-speaking countries "gray" is the American spelling). When a brain is preserved, cortical areas–areas of cortex–appear gray because they contain dense concentrations of cell bodies. What is the cerebral cortex? What does "cortex" mean? (Smaller brain structures like the thalamus and cerebellum also have cortical layers.)
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It refers to a dense outer layer of neurons on any brain structure, not just the cerebrum. The word cortex means rind or shell in Latin. The layer of cortex covers the surface of the cerebrum and goes down into the fissures. This layer averages 3.2 mm thick in human beings, less than a quarter inch. The cerebrum's outermost layer is called the cerebral cortex. The prefrontal area, darkened above for emphasis, is an important area for higher-level thought processes in humans. It consists of everything you see in this figure, which is facing right. The cerebrum (pronounced either SARAH-brum or suh-REE-brum) is the topmost part of the brain. Gyri on the brain–prefrontal areas in black What causes convolutions to form? What is a fissure? A gyrus? The following figure shows major gyri on the human brain. A gyrus is an outward fold similar to a hilltop on the brain. The opposite of a fissure is a gyrus (plural gyri ). Because of this folding, the brain appears to have distinct parts called lobes.įissures–deep folds in the surface of the brain–mark off each lobe. The convolutions form because the rapidly growing brain has different layers of cells that grow at different rates, causing buckling. The convolutions continue to form and deepen for years after a baby is born. Late in embryological development the convolutions begin to form, giving the human brain its distinctive wrinkled appearance. Already the three basic divisions of the central nervous system are visible: the forebrain, midbrain, and hindbrain. Over the first few weeks of development, the front part of the tube thickens. The human nervous system starts as a tube of cells in the developing embryo. These convolutions vastly increase the surface area of the brain. Very conspicuous on the brain are large wrinkles or convolutions. Only when preserved for observation does the brain appear gray and claylike. Brain surgeons say it has the consistency of thick custard. The human nervous system consists of two main parts: (1) the central nervous system (CNS) consisting of the brain and spinal cord, and (2) the peripheral nervous system (PNS), consisting of nerves outside the brain and spinal cord, traveling to every part of the body. What structures make up the central nervous system? They are now thought to modify information processing, not just metabolic functions of neurons, so they should be counted, too. Glial cells number about 60 billion in the cerebral cortex. The number, from 20 billion to a trillion, depends on which cells are included. Each neuron is a highly complex system in itself, surrounded by even larger numbers of glial cells that play a supporting role.Įstimates of the total number of neurons in the human brain vary greatly. Sitting behind the protective shell of the skull, cushioned in a special liquid called cerebrospinal fluid, the brain is a living system composed of many billions of individual nerve cells called neurons. The human brain is the most complex piece of matter in the known universe. Humans take the brain for granted because it is part of their basic package, but brains are amazing things. Your brain is a true wonder of nature, probably the only one that wonders about itself.