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Chapter 1

Chapter 1 - Neuroscience.docx

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Janelle Leboutillier

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Neuroscience: Past, Present, and Future o Neuroscience is a young field of study and was founded recently in the 1970s. The study of the brain, however, is as old as science itself. o The nervous system – the brain, spinal cord, and nerves of the body – is crucial for life and enables you to sense, move, and think. o The origins of neuroscience date back to the archeological record which shows hominid skulls, dating back a million years and more, bearing signs of fata cranial damage, presumably inflicted by other hominids.  As early as 7000 years ago, people were boring holes in each other’s skull a process called trepanation – procedure may have been used to treat headaches or mental disorders, perhaps by giving the evil spirits an escape route.  During these times it was believed that the heart, not the brain, was considered to be the seat of the soul and the repository of memories. This notion was not seriously challenged until the time of Hippocrates. o There appears a very clear correlation between structure and function. Differences in appearance predict differences in function. o The head is specialized for sensing the environment. In the head are the eyes and ears, your nose and tongue. Thus the brain is the organ of sensation. o The most influential scholar was Hippocrates, father of Western medicine, who stated his belief that the brain not only was involved in sensation but also was the seat of intelligence.  This view was not universally accepted.  Aristole, famous Greek philosopher, clung to the belief that the heart was the center of intellect. He proposed the brain to be a radiator for the cooling blood that was overheated by the seething heart. o Galen, Greek physician and writer, embraced the Hippocratic view of brain function.  Galen’s opinions about the brain probably were influenced more by his many careful animal dissections.  Two major parts are evidence: the cerebrum in the front of brain and cerebellum in the back of brain  Cerebrum: rather soft in texture, must’ve been the receipt of sensations, largely concerned with sensation and perception – also repository of memory  Cerebellum: rather hard in texture, must’ve been the commander of muscles, is primarily a movement control center  Galen recognized that to form memories, sensations must be imprinted onto the brain. Naturally, this must occur in the doughy cerebrum.  Galen was also able to cut open the brain and find that it was hollow; in these spaces, called ventricles¸ there is fluid – this discovery fit perfectly with prevailing theory that body functioned according to a balance of four vital fluids.  Sensations were registered and movements initiated by the movement of humors to or from the brain ventricles via the nerves, which were believed to be hollow tubes, like the blood vessels. o Andreas Versalius¸ anatomist added more detail to the structure of the brain from ideas of Galen. o Early seventieth century, French inventors began developing hydraulically controlled mechanical devices.  Notion that the brain could be machinelike. Fluid forced out of the ventricles through the nerves might literally “pump you up” and cause the movement of the limbs.  Rene Descartes, French mathematician and philosopher, did not believe the fluid-mechanical theory was enough to explain human behavior  He reasoned that unlike other animals, people possess intellect and a God- given soul. Thus, he proposed that brain mechanisms control human behavior only to the extent that this behavior resembles that of the beasts.  He believed that the mind is a spiritual entity that receives sensations and commands movements by communicating with the machinery of the brain via the pineal gland.  As we know now, the mind has a physical basis, which is the brain o Brain tissue is divided into two parts: 1. Gray matter 2. White matter, because it was continuous with the nerves of the body, contains the fibers that bring information to and from the gray matter o The nervous system has a central division, consisting of the brain and spinal cord, and a peripheral division, consisting of the network of nerves that course through the body. o Great through in neuroanatomy was the observation that the same general pattern of bumps (gyri) and grooves (sulci and fissures) could be identified on the surface of the brain in every individual  This pattern enables cerebrum into lobes, was the basis for speculation that different functions might be localized to the different bumps on the brain. o A review of the nervous system at the end of the eighteenth century: a. Injury to the brain can disrupt sensations, movement, and thought and can cause death b. Brain communicates with body via nerves c. Brain has different identifiable parts, which probably perform different functions d. Brain operates like a machine and follows the laws of nature o Italian scientist Luigi Galavani and German biologist Emil du Bois-Reymond had shown that muscles can be caused to twitch when nerves are stimulated electrically and that the brain itself can generate electricity.  These discoveries finally displaced the notion that nerves communicate with the brain by the movement of fluid.  New concept that nerves were like “wires” that conduct electrical signals from the brain o Within each nerve of the body there are many thin filaments, or nerve fibers, each one of which could serve as an individual wire carrying information in a different direction o Charles Bell and Francois Magendie  A curious anatomical fact is that just before the nerves attach to the spinal cord, the fibers divide into two branches, or roots. The dorsal root enters toward the back of the spinal cord, and the ventral root enters toward the front.  Bell tested the possibility that these two spinal roots carry information in different directions by cutting each root separately and observing the consequences in experimental animals. He found that cutting only the ventral roots caused muscle paralysis.  Magendie was able to show that the dorsal roots carry sensory information into the spinal cord.  Both Bell and Magendie concluded that within each nerve there is a mixture of wires, some of which bring information into the brain and spinal cord and others that send information out to the muscles. In each sensory and motor nerve fiber, transmission is strictly one-way. The two kinds of fibers are bundled together for most of their length, but they are anatomically segregated when they enter or exit the spinal cord. o In 1811, Bell proposed that the origin of motor fibers is the cerebellum and that destination of the sensory fibers in the cerebrum.  In order to identify functions of the spinal roots, Bell used a technique called experimental ablation method which is a systematic way in which one destroys parts of the brain of interest and test for sensory and motor deficits  Marrie-Jean-Pierre Flourens used this technique on a variety of animals (birds especially) to show that the cerebellum does indeed play a role in the coordination of movement. He also concluded that the cerebrum is involved in sensation and perception  Unlike previous scientists before him, Flourens provided solid experimental support for his conclusions o Franz Joseph Gall, Austrian medical student, believed that bumps on the surface of the skull reflect the bumps on the surface of the brain. He stated that propensity for certain personality traits, such as generosity, secretiveness, and destruct
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