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During the Jendrassik manoeuvre discount 100mg zenegra overnight delivery erectile dysfunction with ms, there is a descending excitatory influence that enhances reflex transmission to motoneurones (MN) buy 100 mg zenegra with visa erectile dysfunction treatment pills, but not (or minimally) to MNs. Taps that failed to produce a tendon jerk are shown as open symbols alongside the appropriate afferent volley size. Dashed lines are linear regression lines for the taps that produced reflex EMG. The data obtained during reinforcement manoeuvres (filled triangles) differ significantly (P < 0. Motor tasks – physiological implications 135 Al-Falahe, Nagaoka & Vallbo, 1990a,b;Vallbo & is shortening against a load, the discharge pattern Al-Falahe, 1990). Spindles in nearby inactive synergists may be amplitudeandvelocitybecausethefusimotoreffects unloaded (Vallbo, 1973, 1974;Burke et al. The discharge of muscle of movement (Bergenheim, Ribot-Ciscar & Roll, spindle endings in the contracting muscle declines 2000;Roll, Bergenheim & Ribot-Ciscar, 2000). Co- during long-lasting contractions by about one-third contractions may involve greater fusimotor drive to over 60 s, even when the presence of increasing EMG the contracting muscles than occurs during isolated activityindicatessomefatigue(Fig. During platform, there is little or no EMG activity in the unloaded phasic shortening contractions, it is likely pretibial muscles, there is a poorly sustained spin- that muscle spindle endings in the contracting mus- dle afferent activity, and manoeuvres that increase clewillbesilenced,andanyperceptualorreflexcues the reliance on the proprioceptive feedback do not will come from other receptors, particularly spin- significantly alter the fusimotor drive in the absence dles in the antagonist (see Ribot-Ciscar & Roll, 1998). However, when the receptor- Spindle endings in the contracting muscle may dis- bearing muscles are activated tonically or phasically charge, but this occurs after the appearance of the to maintain balance their contraction is accompan- first EMG potentials and before the limb has actually ied by an increase in fusimotor drive sufficient to commenced moving. Static fusimotor motoneurones The discharge of both primary and secondary spin- Possible role of the fusimotor system dle endings increases during voluntary contractions during normal movement (Figs. Further evidence indicating a of debate, and it is likely that its importance in the s action consists of an increase in static sensitivity, moment-to-moment control of movement differs in a decrease in the dynamic response of primary end- the cat and man – in part because of the species dif- ings to stretch (though this could be due to a change ferences discussed earlier (see pp. The view in the damping effect of the stiffness of muscle and that some movements can be initiated by first acti- tendon), and a loss of the pause in discharge that vating efferents is now rejected for both species, primaryendingsundergofollowingpassiveshorten- but the extent to which the fusimotor system pro- ing (Vallbo, 1973, 1974;Vallbo et al. In addi- vides a necessary support to voluntary contractions tion, there is an increase in the variability of spindle has not been clarified. Microneurography has been discharge, and the appearance of a negative serial used for ∼35 years, but in this time we have learnt a correlation between successive interspike intervals lot about what the fusimotor system does not do and (Burke, Skuse & Stuart, 1979), something that is a relatively little about its essential contribution to the feature of s drive (see Matthews & Stein, 1969; control of human movement. Role of afferent feedback Dynamic fusimotor motoneurones Is movement possible without afferent feedback? There is some evidence that d drive is increased in addition to s (Kakuda & Nagaoka, 1998). How- Movement is possible without any afferent feed- ever, the study compared the dynamic responses to back from the contracting muscle. This has been stretch of spindle endings in relaxed and contracting demonstrated in patients with large-fibre sensory muscles. Subjects were still able to activate motor axons directed to acutely dener- vated muscles and could voluntarily modulate their Skeleto-fusimotor motoneurones firing rates. There is also some evidence that voluntary activity activates motoneuronesinadditionto motoneu- Necessity for afferent feedback rones during wrist extension (Kakuda, Miwa & Nagaoka, 1998). This finding relied on the use of However, in the absence of afferent feedback, sub- spike-triggeredaveragingtodefineanEMGpotential jects were unable to maintain a steady discharge of closely linked to the afferent spikes, a technique that motoneurones, and the discharge rates in weak, Motor tasks – physiological implications 137 moderate and strong contractions were less than merely indicates that the nervous system will always those reached in control experiments on the same compensateaswellasitcanbeforethesystembreaks subjects. Afferent feedback is also critical when there Speculations on the functional role of drive areunexpecteddisturbancestomovement,suchthat in various motor tasks there is a mismatch between the intended and the achieved movement. Disturbances to the expected Accepting that muscle afferent feedback is critical movement trajectory may be external (due, e. Someformoffeed- dle responsiveness and, in particular, an ability to back is necessary for skilled movement particularly make such adjustments independently of the drive when in novel circumstances, such as walking over on motoneurones. Allmovements are learnt The above data do not identify whether the neces- While this book focuses on spinal circuitry and its sary feedback is of cutaneous, muscle or joint (or role in movement, it should be remembered that even visual) origin. It is likely that the inputs from muscle spindles are sensory receptors, that they all appropriately responding mechanoreceptors are project to higher centres including the sensorimo- integrated to provide a consistent view of the pre- tor cortex, and that they contribute significantly to vailing circumstances and that all can play a role kinaesthetic sensations. It is likely that the impor- in shaping the compensatory motor response. The tance of drive involves more than its spinal reflex evidence is cogent for cutaneous and muscle affer- role. Much infor- Lower-limb muscles mation about the role of different afferent inputs has come from removing individual afferent cues by Contractions of lower-limb muscles are usually blocking specific nerves or from artificially boosting weight-bearing and often cyclical, often eccentric. These are circumstances when create an artificial environment and could give a dis- the co-activated drive can represent a powerful torted view of the importance of different afferent input to muscle spindle endings (see Chapter 11, inputs. This does not mean that the excluded cues The muscles of the hand and forearm are required to were not important or that there was redundancy.

Oral drugs • Noncompliance with recommendations for nondrug mea- also are contraindicated with intestinal obstruction and fecal sures to prevent or treat constipation impaction generic zenegra 100mg otc impotence following prostate surgery. These have long been used The client will: and are safe and effective when used as directed buy zenegra 100 mg free shipping erectile dysfunction self treatment. When used for this purpose, and prevent constipation a gel-like liquid can be squeezed directly from a plant leaf • Regain normal patterns of bowel elimination onto the burned area. Oral aloe is sometimes used as a laxa- • Avoid excessive losses of fluids and electrolytes from tive. However, it is not recommended for this use because it laxative use is a strong stimulant laxative. With oral ingestion, aloe can • Be protected from excessive fluid loss, hypotension, and cause severe cramping and other potentially serious adverse other adverse drug effects, when possible effects including hypokalemia and cardiac dysrhythmias. For long-term use of laxatives or cathartics in clients • Pain (abdominal cramping and distention) related to con- who are elderly, unable or unwilling to eat an adequate stipation or use of laxatives diet, or debilitated, bulk-forming laxatives (eg, Meta- 888 SECTION 10 DRUGS AFFECTING THE DIGESTIVE SYSTEM CLIENT TEACHING GUIDELINES Laxatives General Considerations the next-best action is regular use of a bulk-forming laxa- ✔ Diet, exercise, and fluid intake are important in main- tive (eg, Metamucil) as a dietary supplement. These lax- taining normal bowel function and preventing or treating atives act the same way as increasing fiber in the diet constipation. It is contained in fruits, 2 to 3 days to work and are not effective in relieving acute vegetables, and whole-grain cereals and breads. Walking and other activities aid move- it can lead to life-threatening fluid and electrolyte imbal- ment of feces through the bowel. The defecation urge is usually strongest after eating and Self- or Caregiver Administration the defecation reflex is weakened or lost if repeatedly ✔ Take all laxatives as directed and do not exceed recom- ignored. Regular use may prevent normal bowel func- before taking and follow with additional fluid, if able. Never tion, cause adverse drug reactions, and delay treatment take the drug dry. Adequate fluid intake is essential with for conditions that cause constipation. Doing so may cause a rup- chew), and do not take within 1 hour of an antacid or milk. This helps prevent stomach irritation, abdominal cramping, ✔ After taking a strong laxative, it takes 2 to 3 days of normal and possible vomiting. Frequent use of a strong laxative promotes loss stomach with 8 oz of fluid to increase effectiveness. Mineral oil is probably most useful struction may occur, these agents should not be given as a retention enema to soften hard, dry feces and aid to clients with difficulty in swallowing or adhesions or in their expulsion. In fecal impaction, a rectal suppository (eg, bisacodyl) or unwilling to drink adequate fluids. Oral laxatives are contraindicated when fecal im- painful, stool softeners (eg, docusate sodium) are the paction is present but may be given after the rectal mass agents of choice. For occasional use to cleanse the bowel for endoscopic should be taken to prevent recurrence. If dietary and or radiologic examinations, saline or stimulant cathar- other nonpharmacologic measures are ineffective or tics are acceptable (eg, magnesium citrate, polyethylene contraindicated, use of a bulk-forming agent daily or glycol–electrolyte solution, bisacodyl). Saline cathartics containing magnesium, phosphate, or use is likely to produce laxative abuse. Oral use of mineral oil may cause potentially serious failure because hypermagnesemia, hyperphosphatemia, adverse effects (decreased absorption of fat-soluble vi- or hyperkalemia may occur. Saline cathartics containing sodium salts are contraindi- into the lungs). Thus, mineral oil is not an oral laxative cated in clients with edema or congestive heart failure of choice in any condition, although occasional use in because enough sodium may be absorbed to cause the alert client is unlikely to be harmful. They also should not CHAPTER 61 LAXATIVES AND CATHARTICS 889 be used in clients with impaired renal function or those GI motility and cause constipation. These clients need a following a sodium-restricted diet for hypertension. Stimulant laxatives (eg, a senna preparation for rapid and effective bowel cleansing without signif- or bisacodyl) increase intestinal motility, which is the action icant changes in water or electrolyte balance. These drugs may cause abdominal cramping, which may be lessened by giving small doses three or four times daily.

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However generic 100 mg zenegra with mastercard erectile dysfunction cvs, other components of the ensemble may reflect interactions between dimensions zenegra 100 mg overnight delivery erectile dysfunction normal age, such as the occurrence of a particular response at a particular time in a particular direction. Because there could be more than one way in which the popula- tion could encode such information, it is necessary to understand how individual neurons fire with respect to relevant dimensional features of the task. The three-dimensional graph shows individual neurons (horizontal axis at left), versus time during a DNMS trial. The phases of the DNMS trial are SR, response on the sample lever; NR, response on the nonmatch lever. Each neuron responds with an increased firing rate to di¤erent features or events within the trial. No single neuron is capable of encoding the total information in the task, nor does straightfor- ward examination of the ensemble firing rate lead to derivation of the encoded infor- mation, since each neuron does not always fire during all trials. However, by combining statistical extraction methods applied to the total population of recorded neurons with categorization of individual cell types, the nature of the encoding pro- cess is gradually revealed. The 3-D histograms illustrate several neurons with either sample or nonmatch phase selectivity. The trials were divided according to whether the sam- ple response was to the left (left trial) or right lever (right trial), but there was no dis- tinction in phase responses of these neurons with respect to position. The raster diagram at the top right shows a single, nonmatch, cell with elevated firing only at the nonmatch response, irrespective of response position. This encoding of the DNMS phase by single neurons underlies the di¤erential encoding of the task phase by the ensemble, as shown by the discriminant scores at the bottom right. Further allocation of variance revealed a complementary set of neurons that encoded response position irrespective of DNMS phase. Ensembles of 10–16 neurons were recorded from the rat hippocampus and analyzed via canonical discriminant analysis (Deadwyler et al. The greatest percent of variance (42%) was contributed by a discriminant function (DF1) that di¤erentiated the sample from the nonmatch phase. The graph at the bottom right shows the maximum separation of discriminant scores for DF1 at the sample response (SR) and nonmatch response (NR) events, with scores near zero during intertrial interval (ITI), delay, and last nosepoke during the de- lay (LNP). There was no significant di¤erence in firing at left (left trial) or right (right trial) lever positions. The three-dimensional histograms at the left depict the firing of 12 neurons, 6 sample (toward the lower right) and 6 nonmatch (toward the upper left). Note that the same neurons were active during sample or nonmatch phases on both trial types. The rastergrams (top right) show the activity of a single nonmatch cell. The trials are represented by rows, with each dot indicating a single action recorded potential. Note that the same neurons were active during the sample phase of one trial, but also during phase of the other. The single trial rasters at the top right show the firing of a single left posi- tion cell during both sample and nonmatch responses at the left, but not the right, position. The discriminant scores therefore also selectively reflected ensemble encod- ing of response position in the DNMS task. Note that the variance sources contributing to this ensemble activity clearly encoded information consistent with the features or events of the DNMS task. This is not a necessary outcome of the discriminant analysis because there may be sources of variance encoding other sensory, attentional, or motivational features of the task. However, in each case, once a source of variance is identified, it should be possible to identify single neurons that contribute to that variance, and hence demonstrate the same encoding features. The existence of such unexplained components can be a helpful indicator of the task-relevant firing correlates within a particular behavioral paradigm. Deciphering the Code When neurons interact, they inevitably form multiple contacts, making an analysis of functional characteristics of the network at the level of reconstructing individual syn- apses (weights) di‰cult, if not impossible.

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All have meanings within their group and are useful because they can describe complex notions and ideas in a simple way discount 100 mg zenegra mastercard erectile dysfunction caused by radiation therapy. The difficulty comes when these terms are used inappropriately to the wrong audiences best zenegra 100 mg elite custom erectile dysfunction pump. Jargon (as opposed to gobbledegook) has proliferated because of the increasing tendency to write one document for a number of different audiences (see effective writing), or even for the wrong audience (see false feedback loop). The answer is not to get rid of all 67 THE A–Z OF MEDICAL WRITING these uncommon words completely, but to make sure that we use the right language for our audience. Jokes It is difficult to make these work in the unforgiving black and white of the printed word. Journalese Doctors often use this word as a general term of abuse for vulgar and sensational writing. Journalism At its worst the hounder of innocent princesses and enemy of sensible government. At its best the exposer of unprin- cipled villains and deposers of evil regimes. Whether you love it or loathe it, the practice of journalism provides some useful lessons for those wishing to learn how to communicate effectively (see tabloids). It also provides major opportunities for putting out important public health messages (see press releases). BOOKLIST: journalism • The fight for public health, by Simon Chapman and Deborah Lupton, London: BMJ Books, 1994. Written by two experienced campaigners it shows how the mass media, if understood and used properly, can put across immensely powerful public health messages. This book tries to explain how doctors can learn to write for magazines and newsletters rather than journals. Professional exposition of how to write feature articles for newspapers and magazines. Journals All over the world thousands of journals are published each year, most run by commercial organizations, but some in partnership with professional associations. They contain a blend of material, such as editorials, review articles, letters, obitu- aries and news, but what distinguishes them from magazines is that they include scientific papers sent out for peer review. More recently, through the development of peer review, they have played a key role in validating science (and scientists). In the last few years electronic publishing has challenged a number of assumptions, such as the fact that space to publish is limited and that reviewing can be done only before publication. One of the most likely scenarios seems to be the increasing use of electronic publishing to validate science, and (with luck) the return of journals to their original purpose of communicating exciting advances of knowledge. Whatever happens, the need to understand effective writing will not go away. BOOKLIST: journals • Journal publishing by Gillian Page, Robert Campbell and Jack Meadows, Cambridge: Cambridge University Press, 1997. Unlikely to help anyone with their writing problems, but will delight the fans of peer review. Published to mark the retirement of Stephen Lock as editor of the BMJ, this book has a range of provocative and entertaining articles on all aspects of medical 69 THE A–Z OF MEDICAL WRITING journals. It is particularly interesting to look back at how Richard Smith, the current editor, predicted the development of journals. Journalology The word used to describe the study of matters of interest to editors of learned journals. Key words These are the half dozen or so words that you need to include with an article in order to aid electronic retrieval. Terms from the medical subject head- lines (MeSH) list of Index Medicus should be used. Kill fee If a commissioned article is returned unused authors will sometimes receive a kill fee to compensate them for the time spent (see commissioning). Latin education Not a good preparation for those who want to be able to write effective contemporary English.

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