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Impulses from the CNS travel through so- axons and distinguish between bipolar generic venlor 75 mg overnight delivery, pseudounipolar, matic motor (efferent) fibers and cause the contraction of and multipolar neurons. Explain the nature of the blood-brain barrier and describe CNS for integration. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 355 Astrocyte Nucleus Cytoplasm Mitochondrion Astrocyte foot processes Capillary Basement membrane (continuous) Nucleus Overlapping endothelial cells Erythrocyte Waldrop (a) (b) FIGURE 11. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 356 Unit 5 Integration and Coordination Pseudounipolar Dendritic branches Bipolar Dendrite Multipolar Dendrites Axon FIGURE 11. Pseudounipolar neurons have one process, which splits; bipolar neurons have two processes; and multipolar neurons have many processes (one axon and many dendrites). Sensory Motor Motor (afferent) (efferent) Sensory ending ending Receptors within joints, integument, Skeletal muscle Neurofibril Dendrite skeletal muscles, tissue node and inner ear Myelin sheath Perineurium Intrafascicular blood Somatic Somatic vessel (sensory fibers) (motor fibers) Endoneurium (supports the fasciculi) Central nervous Epineurium Fasciculus system (bundle of nerve fibers) Visceral Visceral (sensory fibers) (autonomic motor fibers) Interfascicular blood vessels Smooth muscle Sensory receptors tissue, cardiac muscle within tissue, and glandular visceral organs Nerve epithelial tissue FIGURE 11. Nervous Tissue and the © The McGraw−Hill Anatomy, Sixth Edition Coordination Central Nervous System Companies, 2001 Chapter 11 Nervous Tissue and the Central Nervous System 357 Dendrite Stimulus Depolorization applied ++++++++++++ Axon ++ ++ (a) ++++++++++++ Stimulus Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ + + + + + + + + + + Nerve +++ + + + + + + + + + Na Na Na K K K K K K K fiber ++ + + + + + + + + + + ++ Na Na Na K K K K K K K (b) Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ +++ + + + + + + + + + Region of depolarization + + + + + + + + + + + + FIGURE 11. Direction of action potential ++ (c) + + + + + + + + + + + + TRANSMISSION OF IMPULSES FIGURE 11. Synaptic transmission is facilitated by the secretion of a neurotransmitter chemical. Objective 8 Explain how a nerve fiber first becomes depolarized and then repolarized. When a Objective 9 Describe the structure of a presynaptic nerve stimulus of sufficient strength arrives at the receptor portion of fiber ending and explain how neurotransmitters are the neuron, the polarized nerve fiber becomes depolarized, and an released. Once depolarization has started, a sequence of ionic exchange occurs along the axon, and the action potential is transmitted (fig. After the axon Action Potential membrane has reached maximum depolarization, the original Two functional properties of neurons are irritability and conduc- concentrations of sodium and potassium ions are reestablished in tivity, both of which are involved in the transmission of a nerve a process called repolarization. Irritability is the ability of dendrites and cell bodies to re- and the nerve fiber is now ready to send another impulse. Conductivity An action potential travels in one direction only and is an is the transmission of an impulse along the axon or a dendrite of all-or-none response. An action potential (nerve impulse) is the actual move- will invariably travel the length of the nerve fiber and proceed ment, or exchange, of sodium (Na+) and potassium (K+) ions without a loss in voltage.

When GFR has declined to infection and cheap 75mg venlor overnight delivery, with hemodialysis, clotting and hemor- 5% of normal or less, the internal environment becomes so rhage. Dialysis does not maintain normal growth and de- disturbed that patients usually die within weeks or months velopment in children. Anemia (primarily a result of defi- if they are not dialyzed or provided with a functioning kid- cient erythropoietin production by damaged kidneys) was ney transplant. It may restore complete molecules through a selectively permeable membrane. In 1999, about 12,500 kidney trans- Two methods of dialysis are commonly used to treat pa- plant operations were performed in the United States. The powerful drugs used to inhibit graft rejec- urea) diffuse into the introduced solution, which is then tion compromise immune defensive mechanisms so that drained and discarded. The procedure is usually done sev- unusual and difficult-to-treat infections often develop. The patient’s blood is pumped through an from a kidney transplant than there are donors. The blood is separated from a bal- dian waiting time for a kidney transplant is currently more anced salt solution by a cellophane-like membrane, and than 900 days. Finally, the cost of transplantation (or dialy- small molecules can diffuse across this membrane. Fortunately for people in the United States, fluid can be removed by applying pressure to the blood and Medicare covers the cost of dialysis and transplantation, filtering it. Hemodialysis is usually done 3 times a week (4 but these life-saving therapies are beyond the reach of to 6 hours per session) in a medical facility or at home. CHAPTER 23 Kidney Function 379 Cortical radial artery convoluted tubules, and cortical collecting ducts are located and glomeruli in the cortex. The medulla is lighter in color and has a stri- Arcuate artery Interlobar ated appearance that results from the parallel arrangement of artery the loops of Henle, medullary collecting ducts, and blood Pyramid vessels of the medulla. The medulla can be further subdi- vided into an outer medulla, which is closer to the cortex, Outer and an inner medulla, which is farther from the cortex. Each lobe consists of a pyramid of artery medulla medullary tissue and the cortical tissue overlying its base Papilla and covering its sides.

Action potentials in atrial muscle adjacent to the AV locity up to 2 m/sec) action potentials throughout the suben- node produce local ion currents that invade the node and docardium of both ventricles discount venlor 75mg visa. Excitation pro- complete excitation of both ventricles takes approximately ceeds throughout the atria at a speed of approximately 1 75 msec. It requires 60 to 90 msec to excite all regions of the assures synchronized contraction of all ventricular muscle atria (Fig. Propagation of the action potential con- cells and maximal effectiveness in ejecting blood. The slower conduction velocity is par- tially explained by the small size of the nodal cells. Less THE ELECTROCARDIOGRAM current is produced by the depolarization of a small nodal The electrocardiogram (ECG) is a continuous record of cardiac electrical activity obtained by placing sensing elec- trodes on the surface of the body and recording the voltage A B differences generated by the heart. The equipment ampli- fies these voltages and causes a pen to deflect proportion- AV bundle SVC ally on a paper moving under it. Positively branch septum charged ions flow toward the negative wire (negative pole) The timing of excitation of various areas of and negatively charged ions simultaneously flow in the op- FIGURE 13. CHAPTER 13 The Electrical Activity of the Heart 225 The combination of two poles that are equal in magnitude and opposite in charge and located close to one another, is called a dipole. The flow of ions (current) is greatest in the region between the two poles, but some current flows at every point surrounding the dipole, reflecting the fact that voltage differences exist everywhere in the solution. Points A and B do because A is closest to the positive pole and B is closest to the negative pole. Positive charges are drawn from the area around point B by the negative end of the dipole, which is relatively near.

Amanda eration has given me the opportunity to make the improvements seen Ellis generic venlor 75mg on line, B. I am indebted to the following individuals for their careful review Last, but certainly not least, I would like to express a special thanks of previous editions of the book: Drs. Dietrichs, in progress, carefully reviewed all changes in the text and all ques- J. The goal is not Abooks are becoming available to students and instruc- only to show external and internal structure per se but also tors, it is appropriate to briefly outline the approach used in to demonstrate that the relationship between brain anatomy this volume. Most books are the result of 1) the philosophic and MRI/CT, the blood supply to specific areas of the CNS approach of the author/instructor to the subject matter and and the arrangement of pathways located therein, the neu- 2) students’ needs as expressed through their suggestions roactive substances associated with pathways, and examples and opinions. The present atlas is no exception, and as a re- of clinical deficits are inseparable components of the learn- sult, several factors have guided its further development. An effort has been made to provide a for- These include an appreciation of what enhances learning in mat that is dynamic and flexible—one that makes the learn- the laboratory and classroom, the inherent value of corre- ing experience an interesting and rewarding exercise. The goal is to make considering that approximately 50% of what goes wrong in- it obvious to the user that structure and function in the CNS side the skull, producing neurological deficits, is vascular- are integrated elements and not separate entities. To emphasize the value of this information, the dis- Most neuroanatomic atlases approach the study of the tribution pattern of blood vessels is correlated with external CNS from fundamentally similar viewpoints. These atlases spinal cord and brain anatomy (Chapter 2) and with inter- present brain anatomy followed by illustrations of stained nal structures such as tracts and nuclei (Chapter 5), re- sections, in one or more planes. Although variations on this viewed in each pathway drawing (Chapter 7), and shown in theme exist, the basic approach is similar. This approach atlases do not make a concerted effort to correlate vascular has several advantages: 1) the vascular pattern is immediately patterns with external or internal brain structures. Also, related to the structures just learned, 2) vascular patterns most atlases include little or no information on neurotrans- are shown in the sections of the atlas in which they belong, mitters and do not integrate clinical examples and informa- 3) the reader cannot proceed from one part of the atlas to tion with the study of functional systems. Following a brief period The ability to diagnose a neurologically compromised pa- devoted to the study of CNS morphology, a significant por- tient is specifically related to a thorough understanding of tion of many courses is spent learning functional systems. This pathway structure, function, blood supply, and the rela- learning experience may take place in the laboratory because tionships of this pathway to adjacent structures. To this end it is here that the student deals with images of representative Chapter 7 provides a series of semidiagrammatic illustrations levels of the entire neuraxis.