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By N. Lukjan. Williams Baptist College.

Circulatory System © The McGraw−Hill Anatomy order 600 mg motrin visa, Sixth Edition Body Companies, 2001 592 Unit 6 Maintenance of the Body the atria (fig. Ventricular Fibrillation Sinus bradycardia Fibrillation is caused by a continuous recycling of electrical waves through the myocardium. Because the myocardium enters a refractory period simultaneously at all regions, this recycling is normally prevented. If some cells emerge from their refractory periods before others, however, electrical waves can be continu- ously regenerated and conducted. The recycling of electrical Sinus tachycardia waves along continuously changing pathways produces uncoordi- (a) nated contraction and an impotent pumping action. Fibrillation can sometimes be stopped by a strong electric shock delivered to the chest—a procedure called electrical defib- rillation. The electric shock depolarizes all the myocardial cells at the same time, causing them to enter a refractory state. The conduction of random recirculating impulses thus stops, and the Ventricular tachycardia SA node can begin to stimulate contraction in a normal fashion. Although this does not correct the initial problem that caused the abnormal electrical patterns, it can keep a person alive long enough to take other corrective measures. Ventricular fibrillation Blood Disorders (b) Because blood is the functional component of the circulatory sys- tem, and because the circulatory system works in such close asso- FIGURE 16. Peripheral arterial pul- be abnormally slow (bradycardia—46 beats per minute in this exam- sations, usually obtained at the radial artery, provide information ple) or fast (tachycardia—136 beats per minute in this example). Capillary filling, following blanching, is an in- Ventricular tachycardia is produced by an ectopic pacemaker in the dicator of peripheral arterial circulation and is generally tested at ventricles. This is done by firmly pressing the thumbnail fibrillation, also shown in (b). If the pinkish color returns quickly to the whitened (blanched) area, circulation is considered normal. Lack Both bradycardia and tachycardia can occur normally of peripheral coloration indicates vascular insufficiency.

When synapsin dissociates from the vesicles generic 400mg motrin overnight delivery, 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.

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Two of cell membranes 600 mg motrin mastercard, which does not permit an osmolality factors are involved. If the osmolality changes in one cause the plasma proteins are negatively charged, they compartment, water moves to restore a new osmotic equi- cause a redistribution of small ions, so that the concentra- librium (see Chapter 2). But the lat- added to an original total body water volume of 42 L, the ter depends on the amount of solute present and the osmo- new total body water volume is 44 L. This fact follows from the definition of the term con- so the new osmolality at equilibrium is (7,980 3,990 centration: concentration amount/volume; hence, volume mOsm)/44 kg 272 mOsm/kg H2O. The main osmotically active ICF at equilibrium, calculated by solving the equation, 272 solute in cells is K ; therefore, a loss of cell K will cause mOsm/kg H2O volume 7,980 mOsm, is 29. From these cal- motically active solute in the ECF is Na ; therefore, a gain culations, we conclude that two thirds of the added water or loss of Na from the body will cause the ECF volume to ends up in the cell compartment and one third stays in the swell or shrink, respectively. This description of events is artificial because, in real- The distribution of water between intracellular and ex- ity, the kidneys would excrete the added water over the tracellular compartments changes in a variety of circum- course of a few hours, minimizing the fall in plasma osmo- stances. The y-axis represents total solute concentration and lution) were added to the ECF. Isotonic saline is isosmotic the x-axis the volume; the area of a box (concentration to plasma or ECF and, by definition, causes no change in times volume) gives the amount of solute present in a com- cell volume. Note that the height of the boxes is always equal, in the ECF and there is no change in osmolality. The osmolality of exposed to a hypertonic environment, and water leaves the both fluids is 285 mOsm/kg H2O. Solutes left behind in the cells become more concen- partment contains 7,980 mOsm and the ECF contains trated as water leaves. Plasma osmolality is low- lated from the amount of solute present (7,980 3,990 ered, and water moves into the cell compartment along the 1,580 mOsm) divided by the final volume (28 14 1 L); osmotic gradient. The entry of water into the cells causes it is equal to 315 mOsm/kg H2O. The final volume of the them to swell, and intracellular osmolality falls until a new ICF equals 7,980 mOsm divided by 315 mOsm/kg H2O or equilibrium (solid lines) is achieved.

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Together have devised the technology for launching rockets into space buy motrin 600mg with visa, they orient the body, coordinate body activities, permit the assimi- curing diseases, mapping the human genome, and splitting atoms. But with all of these achievements, the brain still remains largely Objective 1 Describe the divisions of the nervous system. Neurology, the study of the nervous system, has been re- Objective 2 Define neurology; define neuron. Basic ques- tions concerning the functioning of the nervous system remain Objective 3 List the functions of the nervous system. The immensely complex brain and its myriad of connecting path- ways constitute the nervous system. The peripheral nervous system (PNS) consists of cranial nerves and spinal nerves. Also part of the PNS are the plexuses and additional nerves that arise from the cranial and spinal nerves. The autonomic nervous system (ANS) is a functional subdivision of the nervous system. 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 345 TABLE 11. Meninges (singular, meninx) Group of three fibrous membranes covering the CNS, composed of the dura mater, arachnoid, and pia mater Cerebrospinal fluid (CSF) Clear, watery medium that buoys and maintains homeostasis in the brain and spinal cord Neuron Structural and functional cell of the nervous system; also called a nerve cell Motor (afferent) neuron Nerve cell that transmits action potentials from the CNS to an effector organ, such as a muscle or gland Sensory (efferent) neuron Nerve cell that transmits action potentials from an effector organ to the CNS Nerve Bundle of nerve fibers (elongated portions of neurons) Nerve plexus Convergence or network of nerves Somatic motor nerve Nerve that innervates skeletal muscle; conveys impulses causing muscle contraction Autonomic motor nerve Nerve that innervates smooth muscle, cardiac muscle, and glands; conveys impulses causing contraction (or inhibiting contraction) of smooth muscle and cardiac muscle and secretion of glands Ganglion Cluster of neuron cell bodies outside the CNS Nucleus Cluster of neuron cell bodies within the CNS Tract Bundle of nerve fibers interconnecting regions of the CNS What are the roles of the many chemical compounds within the ory) and to establish patterns of response on the basis of prior brain? The controlling centers of the Thus, broadly speaking, the nervous system has sensory, integra- ANS are located within the brain and are considered part of the tive, and motor functions, all of which work together to maintain CNS; the peripheral portions of the ANS are subdivided into the the internal constancy, or homeostasis, of the body. An instinct also may be called a fixed action pattern; typically, it is genetically specified with little environmental modification. It Functions of the Nervous System is triggered only by a specific stimulus. Some of the basic instincts in humans include survival, feeding, drinking, voiding, and specific vocal- The nervous system is specialized for perceiving and respond- ization. Some ethologists (scientists who study animal behavior) believe ing to events in our internal and external environments.

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However buy motrin 600mg, if potential factors that may affect test performance are measured during the study, these can be included as independent covariables in the analysis. An example may be age as a potential effect modifier of the performance of renography. The potential influence of other possible biases can be explored using sensitivity analysis. Also, in such a pooled analysis the usual performance measures of diagnostic tests can be assessed, as is shown in Chapter 8. Finally, although it is always the aim to minimise the number of lost outcomes or not-performed tests, in most studies these will not be totally avoided. Although associated methodological problems are discussed in Chapter 2, there are various options for the analytical approach to such “missing values” on which professional biostatisticians can give advice. Likelihood ratios with confidence: sample size estimation for diagnostic test studies. The meaning and use of the area under a receiver operating characteristic (ROC) curve. Application of logistic regression to the analysis of diagnostic data: exact modeling of a probability tree of multiple binary variables. Software q For the analysis of test results, including logistic regression for single and multiple tests and confidence intervals for the diagnostic odds ratio, standard statistical software such as SPSS, SAS or BMDP may be used. In SPSS and SAS analysis of the area under the ROC curve (plus confidence intervals) can be performed. For all tables N number of observations (denominator), n number of successes (numerator). Example for small n: A new screening test for a disease is required to have a very low false positive rate that is, high specificity. In a sample of 200 proven non-diseased subjects only one had a positive test result. With this approximation, the half 95% confidence interval for a proportion pˆ n/N is 1. The 95% confidence interval is constructed by subtracting (lower confidence limit) or adding (upper confidence limit) the number from the table to the estimate p.


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