The Human Brain Circulation

This e-book will review special features of the cerebral circulation and how they contribute to the physiology of the brain. It describes structural and functional properties of the cerebral circulation that are unique to the brain, an organ with high metabolic demands and the need for tight water and ion homeostasis. Autoregulation is pronounced in the brain, with myogenic, metabolic and neurogenic mechanisms contributing to maintain relatively constant blood flow during both increases and decreases in pressure. In addition, unlike peripheral organs where the majority of vascular resistance resides in small arteries and arterioles, large extracranial and intracranial arteries contribute significantly to vascular resistance in the brain. The prominent role of large arteries in cerebrovascular resistance helps maintain blood flow and protect downstream vessels during changes in perfusion pressure. The cerebral endothelium is also unique in that its barrier properties are in some way more like epithelium than endothelium in the periphery. The cerebral endothelium, known as the blood-brain barrier, has specialized tight junctions that do not allow ions to pass freely and has very low hydraulic conductivity and transcellular transport. This special configuration modifies Starling's forces in the brain microcirculation such that ions retained in the vascular lumen oppose water movement due to hydrostatic pressure. Tight water regulation is necessary in the brain because it has limited capacity for expansion within the skull. Increased intracranial pressure due to vasogenic edema can cause severe neurologic complications and death.

Modern brain imaging is revolutionizing the study of brain function in health and disease. However, few realize that its origins began in the nineteenth century with Dr. Angelo Mosso's pioneering experiments. A foremost Italian physiologist and scientist, Angelo Mosso studied several patients brought to him with head injuries that exposed their live brains to direct, long-term observation. He took advantage of these rare opportunities to document, for the first time, changes in cerebral blood flow in response to different stimuli, behaviors, and emotions, the very same changes that are now the basis for the measurements underlying modern functional brain imaging. Mosso was widely recognized by his contemporaries for his highly original studies, published both in Italian in 1878 and in German in 1881. Yet there has never been a translation through which this groundbreaking work could be appreciated by the English-speaking world. Indeed, Angelo Mosso's sophisticated experiments were to neuroscience what surgeon William Beaumont's in vivo observations were to gastric physiology fifty years earlier. This unique monograph establishes Mosso's rightful role as the pioneer of brain imaging. Through it, the modern reader, whether expert neuroscientist or interested student, can gain a new perspective on the author's remarkable insights: how behaviors as subtle as thinking about a subject or feeling an emotion produce the changes in pulsations of the brain that he observed and recorded for posterity. Special features of this volume include first a brief summary of Mosso's life. Two pioneers of modern brain imaging, Marcus E. Raichle (winner of the Kavli Prize for Neuroscience) and Gordon M. Shepherd (Yale University Professor of Neurobiology) then review Mosso's work and provide extensive commentary to explain its relevance to modern brain science. The authors not only emphasize Mosso's pioneering role in brain imaging, but also his fundamental contribution to the rise of cognitive neuroscience. The English translation (by historian of medicine Christiane Nockels Fabbri) follows, together with all of the plates and illustrations of the original volume. The result is a classic of neuroscience, now available for wide appreciation by neuroscientists, neurologists, psychologists, psychiatrists, historians of science and medicine, and the general public.

Much of our knowledge of the cerebral circulation has been derived from studies of species other than human. There is increas ing recognition of species differences and concern that studies in animals may be misleading if unquestioningly applied to the human. A dramatic example of this occurred in the early his tory of the study of the circulation of the brain. Galen of Pergamo (131-201 AD) described a rete mirabile or "marvelous network" of blood vessels at the base of the human skull that he must have derived from observations of certain animals. This vascular structure was supplied by the carotid arteries which, after penetrating the cranium,"are divided into a large number of very small and thin branches in the region between the cranium and the dura matter. Then . . . intersecting one another they give the impression of having forgotten their way in the brain. But this is not the case. In fact, these numerous arteries rejoin and unite like the roots of a tree trunk. . . . " The authority of Galen's writings dominated scientific thought for about 1500 years. His description of a rete was unques tioned by Leonardo de Vinci, who included it in his anatomical sketches. William Harvey's remarkable observations led to his definitive account of the circulation of blood.

This presentation describes various aspects of the regulation of tissue oxygenation, including the roles of the circulatory system, respiratory system, and blood, the carrier of oxygen within these components of the cardiorespiratory system. The respiratory system takes oxygen from the atmosphere and transports it by diffusion from the air in the alveoli to the blood flowing through the pulmonary capillaries. The cardiovascular system then moves the oxygenated blood from the heart to the microcirculation of the various organs by convection, where oxygen is released from hemoglobin in the red blood cells and moves to the parenchymal cells of each tissue by diffusion. Oxygen that has diffused into cells is then utilized in the mitochondria to produce adenosine triphosphate (ATP), the energy currency of all cells. The mitochondria are able to produce ATP until the oxygen tension or PO2 on the cell surface falls to a critical level of about 4–5 mm Hg. Thus, in order to meet the energetic needs of cells, it is important to maintain a continuous supply of oxygen to the mitochondria at or above the critical PO2 . In order to accomplish this desired outcome, the cardiorespiratory system, including the blood, must be capable of regulation to ensure survival of all tissues under a wide range of circumstances. The purpose of this presentation is to provide basic information about the operation and regulation of the cardiovascular and respiratory systems, as well as the properties of the blood and parenchymal cells, so that a fundamental understanding of the regulation of tissue oxygenation is achieved.

An essential guide for understanding the inner workings of your brain! Do you really only use 10 percent of your brain? Can a bump to the head really restore memories? Does your brain ever lie to you? Why do you always forget where your glasses are, but never how to read? The brain makes you who you are. This fascinating organ creates your personality and controls your reactions and emotions. It's responsible for how you perceive the world around you--all while controlling hundreds of physical functions like breathing, moving, circulation, and digestion. The brain is simply amazing! The Everything Guide to the Human Brain will help you to unlock the mysteries of the brain. You'll learn how the brain communicates with each part of the body, how it affects your emotional life, why you dream, and how you remember things. And you'll also get in-depth descriptions of brain disorders and how science and medicine are working to heal or reverse them. Written in plain English, this ultimate user's guide will help you learn about the most influential part of your body!

The brain ... There is no other part of the human anatomy that is so intriguing. How does it develop and function and why does it sometimes, tragically, degenerate? The answers are complex. In Discovering the Brain, science writer Sandra Ackerman cuts through the complexity to bring this vital topic to the public. The 1990s were declared the "Decade of the Brain" by former President Bush, and the neuroscience community responded with a host of new investigations and conferences. Discovering the Brain is based on the Institute of Medicine conference, Decade of the Brain: Frontiers in Neuroscience and Brain Research. Discovering the Brain is a "field guide" to the brainâ€"an easy-to-read discussion of the brain's physical structure and where functions such as language and music appreciation lie. Ackerman examines: How electrical and chemical signals are conveyed in the brain. The mechanisms by which we see, hear, think, and pay attentionâ€"and how a "gut feeling" actually originates in the brain. Learning and memory retention, including parallels to computer memory and what they might tell us about our own mental capacity. Development of the brain throughout the life span, with a look at the aging brain. Ackerman provides an enlightening chapter on the connection between the brain's physical condition and various mental disorders and notes what progress can realistically be made toward the prevention and treatment of stroke and other ailments. Finally, she explores the potential for major advances during the "Decade of the Brain," with a look at medical imaging techniquesâ€"what various technologies can and cannot tell usâ€"and how the public and private sectors can contribute to continued advances in neuroscience. This highly readable volume will provide the public and policymakersâ€"and many scientists as wellâ€"with a helpful guide to understanding the many discoveries that are sure to be announced throughout the "Decade of the Brain."