THE
HUMAN BRAIN
THE
HUMAN BRAIN
Your brain is divided into three main regions. Two of them, the brain stem and cerebellum, look after the running of your body. They control your circulation, your breathing, and your posture. The cerebrum, which is much larger, processes information. It is this part of your brain that you use to think. Your brain contains about a trillion nerve cells when you’re born. This number slowly decreases as you get older, because neurons die and cannot be replaced.
CEREBELLUM
The cerebellum is the second smaller division of the brain. It coordinates balance and movement. The brain is located below the cerebrum and in the posterior of the brain. The cerebellum features a central portion called the vermis, and two side portions, one on each side. It is the responsibility the cerebellum to coordinate and modify the resultant activity impulses and orders sent from the cerebrum. It does this by receiving the information from the nerve endings all over the body, such as balance and equilibrium centers in the inner ear, and adjusts and fine tunes these actions by passing the regulating signals to the motor neurons of the brain and spinal cord. Damage to the cerebellum there for results in loss of ability to maintain precise muscular coordination and fine cooperative actions of the motor processes called ataxia).
CEREBRUM
The cerebrum, or forebrain, forms the bulk of the brain. The cerebrum is formed of a large mass of white and gray neural fiber in the upper cranium. It is responsible for the higher thought to process (memory, judgement, reason), processing sensory data, and with initiating willful motor processes, such as voluntary muscle flexion. The cerebrum is composed of two lateral halves, which feature a number of wrinkles, and furrows and which are connected in the middle of the medulla. The cerebrum is descriptively divided into four sections, or lobes, named for the cranial bones, which they are nearest: the frontal lobe, the occipital lobe, the parietal lobe, and the temporal lobe.
Anatomy The adult human brain is a 1.3-kg (3-lb) mass of pinkish-gray jellylike tissue made up of approximately 100 billion nerve cells and other tissues.A clear liquid, the cerebrospinal fluid, bathes the entire brain and fills a series of four cavities, called ventricles, near the center of the brain.The brain has three distinct but connected parts: the cerebrum (the Latin word for brain)—two large, almost symmetrical hemispheres; the cerebellum ("little brain")—two smaller hemispheres located at the back of the cerebrum; and the brain stem—a central core that gradually becomes the spinal cord. The brain stem regulates heartbeat, breathing, and other vital functions.The brain and the spinal cord together make up the central nervous system, which communicates with the rest of the body . LanguageLanguage involves specialized cortical regions in a complex interaction that allows the brain to comprehend and communicate abstract ideas. The motor cortex initiates impulses that travel through the brain stem to produce audible sounds. Neighboring regions of motor cortex, called the supplemental motor cortex, are involved in sequencing and coordinating sounds. Broca's area of the frontal lobe is responsible for the sequencing of language elements for output. The comprehension of language is dependent upon Wernicke's area of the temporal lobe. Other cortical circuits connect these areas.
MemoryMemory is usually considered a diffusely stored associative process—that is, it puts together information from many different sources. Although research has failed to identify specific sites in the brain as locations of individual memories, certain brain areas are critical for memory to function. Immediate recall—the ability to repeat short series of words or numbers immediately after hearing them—is thought to be located in the auditory associative cortex. Short-term memory—the ability to retain a limited amount of information for up to an hour—is located in the deep temporal lobe. Long-term memory probably involves exchanges between the medial temporal lobe, various cortical regions, and the midbrain.
The Autonomic Nervous SystemThe autonomic nervous system regulates the life support systems of the body reflexively—that is, without conscious direction. It automatically controls the muscles of the heart, digestive system, and lungs; certain glands; and homeostasis—that is, the equilibrium of the internal environment of the body . The autonomic nervous system itself is controlled by nerve centers in the spinal cord and brain stem and is fine-tuned by regions higher in the brain, such as the midbrain and cortex. Reactions such as blushing indicate that cognitive, or thinking, centers of the brain are also involved in autonomic responses.
Brain DisordersThe brain is guarded by several highly developed protective mechanisms. The bony cranium, the surrounding meninges, and the cerebrospinal fluid all contribute to the mechanical protection of the brain. In addition, a filtration system called the blood-brain barrier protects the brain from exposure to potentially harmful substances carried in the bloodstream.Brain disorders have a wide range of causes, including head injury, stroke, bacterial diseases, complex chemical imbalances, and changes associated with aging.
Head Injury Head injury can initiate a cascade of damaging events. After a blow to the head, a person may be stunned or may become unconscious for a moment. This injury, called a concussion, usually leaves no permanent damage. If the blow is more severe and hemorrhage (excessive bleeding) and swelling occur, however, severe headache, dizziness, paralysis, a convulsion, or temporary blindness may result, depending on the area of the brain affected. Damage to the cerebrum can also result in profound personality changes.Injury to the brain stem is even more serious because it houses the nerve centers that control breathing and heart action. Damage to the medulla oblongata usually results in immediate death. StrokeA stroke is damage to the brain due to an interruption in blood flow. The interruption may be caused by a blood clot , constriction of a blood vessel, or rupture of a vessel accompanied by bleeding. A pouchlike expansion of the wall of a blood vessel, called an aneurysm , may weaken and burst, for example, because of high blood preasure. A massive stroke can cause a one-sided paralysis (hemiplegia) and sensory loss on the side of the body opposite the hemisphere damaged by the stroke.