The spinal cord is the traditional starting point for a detailed consideration of the central nervous system (CNS). It is a uniformly organized part of the CNS and one of the simplest (in a relative sense), but many principles of cord function also apply to other levels of the nervous system. At the same time, the spinal cord is extraordinarily important in the day-to-day activities we…
The ongoing activity and output of the central nervous system (CNS) are greatly influenced, and sometimes more or less determined, by incoming sensory information. An example is our constant awareness of the position of our limbs in space and the use of this awareness in guiding movements. The basis of this incoming sensory information is an array of sensory receptors, a a Receptor is a term…
Early in the last century, Ramón y Cajal and others used the Golgi stain to demonstrate that the nervous system is a collection of individual neurons (e.g., see Fig. 1.16A ) rather than a vast syncytial network, as some had alleged. An obvious corollary of this demonstration is that neurons must have mechanisms by which they communicate with one another. Although there are some instances in…
We depend on our brains to process and convey huge quantities of information rapidly and reliably. As a biological system, the brain must do this using neurons and their axons and synapses rather than wires and transistors. This makes the task more difficult, because it is substantially harder to move electrical signals around in the aqueous medium inside and surrounding neurons than in more conventional electronic…
Turtles can walk around for hours with no oxygen supply to their brains. In contrast, our brains are absolutely dependent on a continuous supply of well-oxygenated blood. After just 10 seconds of brain ischemia, we lose consciousness. After 20 seconds, electrical activity ceases, and after just a few minutes, irreversible damage usually begins. Corresponding to this metabolic dependence, blood vessels in the central nervous system (CNS),…
The cavity of the embryonic neural tube develops into a continuous, fluid-filled system of ventricles lined with ependymal cells; each division of the central nervous system (CNS) contains a portion of this ventricular system. Cerebrospinal fluid (CSF) is formed within the ventricles, fills them, and emerges from apertures in the fourth ventricle to fill the subarachnoid space. CSF is responsible for suspension of the brain through…
Living brain is soft and mushy, despite the network of cytoskeletal proteins contained in neurons and glial cells. Without support of some kind, the central nervous system (CNS) would be unable to maintain its shape, particularly as we walk and run around and occasionally bump our heads. The brain and spinal cord are protected from outside forces by their encasement in the skull and vertebral column,…
The human central nervous system (CNS) is composed of the brain and spinal cord. This chapter briefly discusses the major surface and internal structures of the brain (summarized in Fig. 3.26 ) and, together with the following six chapters, lays the groundwork for the more detailed discussions of the functional anatomy of the CNS in ensuing chapters. The Long Axis of the CNS Bends at the…
As complex as the human nervous system is, it starts out embryonically as a simple, tubular, ectodermal structure. An understanding of the development of the nervous system helps make sense of its adult configuration and organization. Similarly, congenital malformations of the central nervous system (CNS) are more easily understood in light of its embryological development; such malformations provide clues that aid in the understanding of normal…
The aims of this book are to present and explain some basic anatomical facts about how the brain is put together, to discuss aspects of how it works, and to present clinical features to aid in application and retention. This introductory chapter describes in a general way the subdivisions of the nervous system then focuses on the cellular elements found within it and the anatomical specializations…
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Chapter 1 1. b. Lemniscus, fasciculus, and peduncle all refer to white matter structures, leaving putamen as the logical choice. The putamen is in fact a large nucleus that is part of the basal ganglia. 2. a. The lenticular nucleus is a major component of the basal ganglia, located subcortically in each cerebral hemisphere (see Fig. 1.1 and Table 1.1 ). 3. c. The midbrain, pons,…
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The nervous system is a lot less able to repair itself after damage than some other organs are, but that doesn't mean it can't change. There's extensive adjustment of connections during development, but even in adult brains, synapses all over the nervous system modify their strength over timescales ranging from seconds to years. Some of these modifications are the basis of normal learning and memory. There…
There is a whole sphere of mental activity that goes beyond simple perception of stimuli and logical formulation of responses. We have drives and urges, and most of our experiences are emotionally colored. This emotional coloring and its relationship with basic drives is the province of the limbic system . The hypothalamus regulates autonomic function and drive-related behavior, and limbic structures serve as bridges between the…
The cerebral cortex is ultimately the part of the CNS that makes us human. Other parts of the CNS like sensory pathways bring in raw data, the reticular activating system adjusts levels of excitability, but the cortex is where events are analyzed, plans are hatched, and responses are formulated. The cerebral cortex is a big sheet of repeated functional modules , with the operations of different…
Photoreceptors throughout the animal kingdom use G protein–coupled transduction mechanisms for added sensitivity, but they pay a price in speed: images need to stay still on the retina for a tenth of second or so at a time to be seen clearly. And for animals with a fovea (like us), images need to stay still on precisely that small part of the retina. All animals with…
The cerebellum helps coordinate movement by sampling most kinds of sensory information, comparing current movements with intended movements, and issuing planning or correcting signals. The comparisons are made in a uniform, precisely organized, cerebellar cortex, and the planning or correcting signals are issued through a set of deep cerebellar nuclei. Because its output is concerned with coordination of movement and not with perception, cerebellar lesions cause…
Historically, the basal ganglia have been considered as major components of the motor system. In fact, they have a much broader role than that and are probably involved to some extent in most forebrain functions. However, their relationship to movement is their best understood aspect, and that is what shows up clinically in disorders like Parkinson disease and Huntington disease. The interrelationships of the basal ganglia…
The firing rates of our motor neurons, and therefore the states of contraction of our muscles, are determined by multiple influences. Simple reflex arcs like the stretch reflex and more complex motor programs like the basic pattern generator for walking are built into the spinal cord and brainstem. Various descending pathways influence these reflex arcs and motor programs, as well as the motor neurons themselves. Finally,…