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Recent evidence suggests that hydrea 500 mg generic, while synapsins might have a role in synaptogenesis generic 500mg hydrea free shipping, they also regulate the supply of vesicles to the release pool (Hilfiker et al buy generic hydrea 500mg on-line. Experiments in vitro have shown that dephosphorylated synapsin I causes growth and bundling of actin filaments which are a major component of neuronal microfilaments generic hydrea 500mg without prescription. Such findings form the basis of the hypothesis that synapsin I forms a ternary complex with transmitter storage vesicles and the neuronal cytoskeleton, thereby confining vesicles to a reserve pool (Fig. Phosphorylated synapsin dissociates from the vesicles and F-actin, reduces the number of vesicle anchoring sites, and so frees the vesicles to the release pool. Synapsin I is the substrate for several protein kinases but one of these, Ca2/calmodulin protein kinase II (CAM kinase II), is bound to vesicle membranes to some extent. It is thought that phosphorylation of synapsin I by CAM kinase II is triggered by the influx of Ca2. This process would enable synapsin to act as a regulator of the balance between the releasable and reserve pools of vesicles. For example, neuronal depolarisation increases the amount of free synapsin in the cytosol and microinjection of CAM kinase II into the terminals of the squid giant axon or brain synaptosomes increases depolarisation- evoked transmitter release. By contrast, injection of dephosphorylated synapsin I into either the squid giant axon or goldfish Mauthner neurons inhibits transmitter release. It has also been suggested that synapsin promotes vesicle clustering by a process which is not dependent on phosphorylation. It achieves this by forming cross-bridges between vesicles and by stabilising the membranes of the aggregated vesicles, thereby enabling them to cluster in the active zone without fusing with each other or the axolemma. When synapsin dissociates from the vesicles, as occurs during neuronal excitation, this membrane-stabilising action is lost. This would enable fusion of the membranes of vesicles, clustered near the active zone, with the axolemma. This scheme is supported by evidence that vesicles near the active zone have much lower con- centrations of synapsin than those located more remotely (Pieribone et al. For instance, it has been suggested that they might also regulate the kinetics of release, downstream of the docking process. VESICULAR EXOCYTOSIS Once vesicles detach from the cytoskeleton they are free to participate in the release process but our understanding of precisely how this is brought about is still sketchy, despite the wealth of information which has accumulated over recent years. What is clear is that it involves a complex cascade of regulatory processes focusing on proteins bound to vesicle membranes, the axolemma and some cytoplasmic factors (see Calakos 96 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION Figure 4. An increase in intracellular Ca2 triggers phosphorylation of synapsin I which dissociates from the vesicular membrane. This frees the vesicles from the fibrin microfilaments and makes them available for transmitter release at the active zone of the nerve terminal and Scheller 1996). The following sections will deal with those factors about which most is known and which are thought to have a prominent role in exocytosis. The extent to which this scheme explains release from large dense-cored vesicles is unclear, not least because these vesicles are not found near the active zone. DOCKING AND FUSION Because exocytosis is so rapid, it is believed that Ca2 must trigger release from vesicles which are already docked at the active zone. The processes leading to docking and fusion of the vesicle with the axolemma membrane are thought to involve the formation of a complex between soluble proteins (in the neuronal cytoplasm)and those bound to vesicular or axolemma membranes. Much of this evidence is based on studies of a wide range of secretory systems (including those in yeast cells)but which are thought to be conserved in mammalian neurons. From evidence collected to date, a scheme has emerged, known as the SNARE hypothesis (see Sollner and Rothman 1994)(Fig. Evidence, largely derived from studies of the Golgi apparatus, suggests that SNAPs have a general role in protein± protein interactions underlying membrane fusion. It is envisaged that this complex of the two SNARES enables sequential binding of the soluble SNAPs and NSF.
The central H zones thus contain only thick filaments on a single row of dark thick myofilaments in this transverse sec- that are not overlapped by thin filaments hydrea 500 mg fast delivery. There are numerous sarcomeres within each When a muscle is stimulated to contract trusted 500 mg hydrea, it decreases in myofibril that are out of the plane of the section (and out of the length as a result of the shortening of its individual fibers discount hydrea 500 mg free shipping. A better appreciation of the three-dimensional struc- Shortening of the muscle fibers purchase hydrea 500 mg with amex, in turn, is produced by shorten- ture of a myofibril can be obtained by viewing the myofibril in ing of their myofibrils, which occurs as a result of the shorten- transverse section. As the seen that the Z lines are actually disc-shaped (Z stands for sarcomeres shorten in length, however, the A bands do not Zwıschenscheibe, a German word meaning “between disc”), and shorten but instead appear closer together. The I bands—which that the thin filaments that penetrate these Z discs surround the represent the distance between A bands of successive thick filaments in a hexagonal arrangement. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 9 Muscular System 243 Sarcoplasm Skeletal muscle fiber Nucleus I band Sarcolemma H zone (c) A band (a) Z line Actin myofilaments Myofibrils Myosin myofilaments (b) H zone Sarcomere H zone A band I band Myofilaments Z line FIGURE 9. The thin actin filaments composing the I band do not of the elbow, for example, occurs against the force of gravity and shorten, however. Close examination reveals that the length of the weight of the objects being lifted. The tension produced by the thick and thin myofilaments remains constant during muscle the contraction of each muscle fiber separately is insufficient to contraction. Shortening of the sarcomeres is produced not by overcome these opposing forces, but the combined contractions shortening of the myofilaments, but rather by the sliding of thin of large numbers of muscle fibers may be sufficient to overcome filaments over and between thick ones. In the process of contrac- them and flex the elbow as the muscle fibers shorten. The central H bands remains relatively constant throughout the shortening process thus get shorter and shorter during contraction. If the opposing forces are too great or if the number of muscle fibers activated is too few to shorten the muscle, however, an isometric contraction is produced, and movement does not occur. Isotonic and Isometric Contractions In order for muscle fibers to shorten when they contract, they must generate a force that is greater than the opposing forces isotonic: Gk. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 244 Unit 4 Support and Movement Myofibril Nucleus Sarcomere Muscle fiber (b) Myofibril (a) (c) FIGURE 9. Tissues and Organs: A Text-Atlas of Scanning Electron Microscopy © 1979 W. A nerve im- A nerve serving a muscle is composed of both motor and sensory pulse reaching the axon terminal causes the release of acetyl- neurons. Each motor neuron has a threadlike axon that extends choline into the neuromuscular cleft of the neuromuscular from the CNS to a group of skeletal muscle fibers. As this chemical mediator contacts the receptor sites of skeletal muscle fibers, the axon divides into numerous branches the sarcolemma, it initiates physiological activity within the called axon terminals. The axon terminals contact the sar- muscle fiber, resulting in contraction. The area consisting of the motor end plate and the cell membrane of a muscle fiber is known as the neuromuscular Motor Unit (myoneural) junction. A motor unit consists of a single motor neuron and the aggrega- tion of muscle fibers innervated by the motor neuron (fig. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 Chapter 9 Muscular System 245 A I H Z Z Z FIGURE 9. The A bands remain the same length during contraction, but the I and H bands narrow progressively and eventually may be obliterated. Most muscles have an innervation ratio of 1 motor neuron for thigh muscle may vary from 1:100 to 1:2,000. Muscles capable of precise, dexter- innervate smaller numbers of muscle fibers have smaller cell ous movements, such as an eye muscle, may have an innervation bodies and axon diameters than neurons that have larger in- ratio of 1:10. The smaller neurons also are stimulated by movements, such as those of the thigh, may have innervation ra- lower levels of excitatory input. The larger motor All of the motor units controlling a particular muscle, units are activated only when very forceful contractions are however, are not the same size. Muscular System © The McGraw−Hill Anatomy, Sixth Edition Companies, 2001 246 Unit 4 Support and Movement tages in physical competition, they also can have serious side ef- fects. These include gonadal atrophy, hypertension, induction of malignant tumors of the liver, and overly aggressive behavior, to name just a few. Draw three successive sarcomeres in a myofibril of a resting muscle fiber.
Urinary System © The McGraw−Hill Anatomy discount hydrea 500mg mastercard, Sixth Edition Body Companies purchase 500 mg hydrea overnight delivery, 2001 Chapter 19 Urinary System 695 CLINICAL PRACTICUM 19 purchase hydrea 500mg. She describes the pain as intermittent and crampy discount hydrea 500 mg without prescription, but de- nies any fever or blood in her urine. Physical exam shows a nontender ab- domen and no evidence of costovertebral angle tenderness. Routine urinalysis shows minimal red blood cells, no white blood cells, and no bacteria. What effect does this have on the ureter as demonstrated by the postcontrast image? Precontrast image Postcontrast image Chapter Summary Introduction to the Urinary System 3. The end product of the deliver blood to peritubular capillaries which is folded into rugae. These urinary system is urine, which is voided surrounding the nephron tubules. Each kidney is contained by a renal tubules are drained into papillary during ejaculation. The female capsule and divided into an outer renal ducts that extend through the renal urethra is much shorter than that of a cortex and an inner renal medulla. Micturition is controlled by reflex centers the minor calyces and then into the major calyces, which drain into the 1. Urine is channeled from the kidneys to in the second, third, and fourth sacral renal pelvis. From there, urine flows the urinary bladder by the ureters and segments of the spinal cord. Urinary System © The McGraw−Hill Anatomy, Sixth Edition Body Companies, 2001 696 Unit 6 Maintenance of the Body Review Activities Objective Questions (c) the urinary bladder. Which of the following statements about development process lead to a better concave medial border of the kidney metanephric kidneys is true? List four common congenital (c) They are the third pair of kidneys to malformations of the urinary system. Essay Questions pyuria, oliguria, polyuria, uremia, and (d) adipose capsules. Describe the location of the kidneys in enters directly into relation to the abdominal cavity and the Critical-Thinking Questions (a) the renal calyces. Describe how the kidney is supported urinary system rather than the excretory against the posterior abdominal wall. Which of the following statements is this support related to the condition 2. Treatment with sulfa medications such as concerning the kidneys is false? Trace a drop of blood from an interlobular spectrum antibiotics such as tetracycline (b) They each contain 8 to 15 renal artery through a glomerulus and into an or ampicillin usually clear up the pyramids. What is (c) They each have two distinct vessels through which the blood passes. The neighborhood day-care center won’t third and fifth lumbar vertebrae. A renal stone (calculus), would most You’ve tried to toilet train your likely cause stagnation of urine in which 5. In a male, trace the path of urine from the site of filtration at the renal corpuscle to 15-month-old boy, but you haven’t made portion of the urinary system? List in order all the structures through which the urine your efforts, or would it be better to wait? What functions of a real kidney does an (d) the renal pelvis artificial kidney (dialysis machine) fail to (e) the urethra types of nephrons found in a kidney.
Because the brain buy cheap hydrea 500mg line, as sectioned at autopsy or in clini- blood supply to these parts of the neuraxis cheap 500 mg hydrea mastercard, one can also cor- cal pathologic conferences generic hydrea 500mg with visa, is viewed as an unstained speci- relate the deficits seen when the same vessels are occluded 500 mg hydrea with mastercard. The diencephalon and basal nuclei section of this chapter uses ten cross-sections to illustrate internal anatomy. It should be emphasized that 8 of these 10 sections (those parallel to Chapter 5 each other) are all from the same brain. This chapter has been revised with special emphasis on in- The internal anatomy of the brainstem is commonly creasing the correlation between anatomical and clinical in- taught in an anatomical orientation. This new edition retains the quality and inherent tures, such as the vestibular nuclei and colliculi, are “up” in strengths of the line drawings and the stained sections being the image, while anterior structures, such as the pyramid located on facing pages in this chapter. However, when ative approach (described below) is introduced that allows the brainstem is viewed in the clinical setting, as in CT or the use of these images in their classic Anatomical Orienta- MRI, this orientation is reversed. In the clinical orientation, tion and, at the same time, their conversion to the Clinical posterior structures (4th ventricle, colliculi) are “down” in Orientation so universally recognized and used in clinical the image while anterior structures (pyramid, basilar pons, imaging techniques. Chapter 5 consists of six sections covering, in sequence, Recognizing that many users of this book are pursuing a the spinal cord, medulla oblongata, cerebellar nuclei, pons, health care career (as a practitioner or teacher of future clin- midbrain, and diencephalon and basal nuclei, all with MRI. The left-hand page contains a la- First, it allows correlation of the size, shape, and configura- beled line drawing of the stained section, accompanied by a tion of brainstem sections (line drawings and stained slices) figure description, and a small orientation drawing. Second, it offers the tion part of the line drawing is printed in a 60% screen of user the opportunity to visualize how nuclei, tracts (and their black, and the leader lines and labels are printed at 100% somatotopy) and vascular territories are represented in MRI black. Understanding the brain in the Clinical Orientation ture, reduces competition between lines, and makes the il- (as seen in MRI or CT) is extremely important in diagnosis. To successfully introduce MRI and CT in the brainstem por- Beginning with the first spinal cord level (coccygeal, Fig- tion of chapter 5, a continuum from Anatomical Orientation ure 5-1), the long tracts that are most essential to under- to Clinical Orientation to MRI needs to be clearly illustrated. These tracts are the posterior column– line drawing on the facing page (page with the stained section) medial lemniscus system, the lateral corticospinal tract, and in Anatomical Orientation; 2) showing how this image is the anterolateral system. In the brainstem, these tracts are flipped top to bottom into a Clinical Orientation; and 3) fol- joined by the colorized spinal trigeminal tract, the ventral lowing this flipped image with (usually) T1 and T2 MRls at trigeminothalamic tract, and all of the motor and sensory levels comparable to the accompanying line drawing and 6 Introduction and Reader’s Guide stained section (Fig. This approach retains the anatom- ical strengths of the spinal cord and brainstem sections of chapter 5 but allows the introduction of important concepts regarding how anatomical information is arranged in images utilized in the clinical environment. Every effort has been made to use MRI and CT that match, as closely as possible, the line drawings and stained sections in the spinal cord and brainstem portions of chapter 5. Recog- nizing that this match is subject to the vicissitudes of angle and individual variation, special sets of images were used in chap- ter 5. The first set consisted of T1- and T2-weighted MRI 1-5 Computed Tomography (CT) of a patient following injection generated from the same individual; these are identified, re- of a radiopaque contrast media into the lumbar cistern. In this exam- spectively, as “MRI, T1-weighted” and “MRI, T2-weighted” ple, at the medullary level (a cisternogram), neural structures appear in chapter 5. The second set consisted of CT images from a grey and the subarachnoid space appears light. This contrast media diffused throughout the spinal the forebrain portion of chapter 5. Many anatomic features and cranial subarachnoid spaces, outlining the spinal cord and seen in the forebrain stained sections are easily identified in brainstem (Fig. These particular MRI are not labeled so structures as grey surrounded by a light subarachnoid space; as to allow the user to develop and practice his/her inter- this is a “CT myelogram”. The various subsections of chapter 5 can be levels (grey brain, light CSF) is a “CT cisternogram”. These used in a variety of ways and will accommodate a wide range designations are used in chapter 5. The three-dimensional anatomy of internal structures in the CNS can also be studied in stained sections that correlate sim- ilar structures in different planes. The photographs of stained axial and sagittal sections and of MRIs in Chapter 6 are orga- nized to provide four important levels of information. First, Anatomical orientation Clinical orientation the general internal anatomy of brain structures can be easily identified in each photograph. Second, axial photographs are on left-hand pages and arranged from dorsal to ventral (Fig- ures 6-1 to 6-9), whereas sagittal photographs are on right- hand pages and arranged from medial to lateral (Figures 6-2 to 6-10). This setup, in essence, provides complete repre- sentation of the brain in both planes for use as independent MRI, T1 weighted image study sets (axial only, sagittal only) or as integrated/corre- lated sets (compare facing pages). Third, because axial and sagittal sections are on facing pages and the plane of section of each is indicated on its companion by a heavy line, the reader can easily visualize the positions of internal structures in more MRI, T2 weighted image than one plane and develop a clear concept of three-dimen- sional topography.