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By P. Folleck. Louisiana College.

The metal wire inside the impulses are conducted backwards (anti- the cable is well insulated and has very low- dromic)due discount doxazosin 1mg online atrophic gastritis symptoms webmd,forexample purchase 2 mg doxazosin with amex gastritis ulcer medicine,toelectricalstimula- level resistance, reducing current loss to a tion of nerve fibers from an external source minimum. C) conduct much faster (up to 80 m/s = 180 Propagation of action potentials: The start mph in humans). In the internode regions, a ofanactionpotentialisaccompaniedbyabrief myelin sheath (! The fibers from the surroundings; thus, longitudi- cell membrane that previously was inside nal currents strong enough to generate action negative now becomes positive ( +20 to potentials can travel further down the axon +30mV), thus creating a longitudinal poten- (ca. This results in more rapid tial difference with respect to the adjacent, conduction because the action potentials are still unstimulated nerve segments (internal generated only at the unmyelinated nodes of –70 to –90mV;! This is followed by a Ranvier, where there is a high density of Na+ passive electrotonic withdrawal of charge from channels. This results in rapid, jump-like pas- the adjacent segment of the nerve fiber, caus- sage of the action potential from node to node ing its depolarization. Thesaltatorylengthis another action potential is created in the adja- limited since the longitudinal current (1 to cent segment and the action potential in the 2nA) grows weaker with increasing distance previous segment dissipates (! Before it drops below the threshold Because the membrane acts as a capacitor, level,thesignalmustthereforeberefreshedby the withdrawal of charge represents a capaci- a new action potential, with a time loss of tating (depolarizing) flow of charge that be- 0. Because of the rela- fiber limits the spread of depolarization, as de- tively high Ri of nerve fiber, the outward loops scribed above, the axon diameter (2r) also af- of current cross the membrane relatively close fectstheconductionvelocity,θ(! R ispro-i to the site of excitation, and the longitudinal portional to the cross-sectional area of the current decreases as it proceeds towards the nerve fiber (πr ),2 i. Atthesametime,depolarizationin- therefore require fewer new APs per unit of creasesthedrivingforce(=Em–EK;! K+ fluxing out of the cell therefore fiberdiameterareaccompaniedbyan increase accelerates repolarization. Hence, distal action in both fiber circumference (2πr) and mem- potentials are restricted to distances from branecapacity,K(K! Althoughθdecreases, which the capacitative current suffices to the beneficial effect of the smaller Ri predomi- depolarizethemembranequicklyandstrongly nates because of the quadratic relationship. Otherwise, the Na+ channels will be deactivated before the threshold potential is 48 reached (! Continuous (1a, 1b) and saltatory propagation (2) of action potentials AP AP Myelin sheath Na+ Na+ Action potential (AP) Na+ Depolarization Na+ Action potential Rest 1a Refractory + Na+ Na AP Depo- Depolarization larization 1b 2 B. Pulse propagation (action currents) in myelinated and unmyelinated nerve fibers AP AP 1nA 1nA AP 1 2 ms 2 0. Classification of nerve fibers (in humans) Fiber type Function according to fiber type Diameter Conduction (Lloyd and Hunt types I–IV) (µm) rate (m/s) Aα Skeletal muscle efferent, afferents in muscle 11–16 60 – 80 spindles (Ib) and tendon organs (Ib) Aβ Mechanoafferents of skin (II) 6 –11 30 – 60 Aγ Muscle spindle efferents Aδ Skin afferents (temperature 1– 6 2 – 30 and „fast“ pain) (III) B Sympathetic preganglionic; 3 3 –15 visceral afferents C Skin afferents (“slow” pain); 0. They can facilitate or inhibit nerve cell from an external source, current the neuronal transmission of information or flows from the positive stimulating electrode processthemwithotherneuronalinput. Atthe (anode) into the neuron, and exits at the nega- chemical synapse, the arrival of an action tive electrode (cathode). Depending on distance from each other, then stimulating the the type of transmitter and receptor involved, nerve (containing multiple neurons) and rec- the effect on the postsynaptic membrane may ording the time it takes the summated action either be excitatory or inhibitory, as is de- potential to travel the known distance. In the case of the motor body to high-voltage electricity, especially end-plate (! Some of the electrical outlet) and low contact resistance vesicles are already docked on the membrane (barefeet,bathtubaccidents),primarilyaffects (active zone), ready to exocytose their con- the conduction of impulses in the heart and tents. Direct current usually acts as a stimulus The higher the action potential frequency in only when switched on or off: High-frequency the axon the more vesicles release their con- alternating current (! An action potential increases the open hand, cannot cause depolarization but heats probability of voltage-gated Ca2+ channels in the body tissues. A1), Synapses connect nerve cells to other nerve which triggers the interaction of syntaxin and cells (also applies for certain muscle cells) as SNAP-25 on the presynaptic membrane with well as to sensory and effector cells (muscle synaptobrevin on the vesicle membrane, and glandular cells). Ontheotherhand,Ca2+activatescal- nexons) in the region of gap junctions cium-calmodulin-dependent protein kinase-II (! Chemical synapse Na+ AP 1 00 2 Presynaptic action potential –80 Calmodulin Presynaptic Ca2+ ending 3 2+ Ca2+ influx 0 Ca ICa Vesicle –0. As a therefore increases the excitability of the post- result, the more recent rise in [Ca2+]i builds on synaptic neuron (! Hence, acetylcholine (at M2 and M3 receptors; thefirststimulusfacilitatestheresponsetothe!

This chapter will present overviews of different imaging techniques buy discount doxazosin 4 mg gastritis diet , principles of optical imaging (see Figure 5 cheap 1 mg doxazosin nervous gastritis diet. The attenuation of these photons as they pass through tissue and strike silver nitrate film or a fluorescent screen reveals underlying anatomic structures within the interrogated tissue volume. To detect function rather than simply reflecting anatomic structures, functional imaging tech- niques in general rely upon similar principles and utilize various energy sources and detectors. Functional related changes in nervous tissue trigger water movement into or out of cells or alter the uptake of glucose or other tracers that are indicative of cellular metabolism. Scattered Light from Cortex to Scattered Light Optical Detector from Neuropil and Hemoglobin to Incident Light Optical Detector Arteries: Brain - Neurons Oxyhemoglobin and Glia Veins: Deoxyhemoglobin FIGURE 5. Two types of optical imaging approaches: at macro (whole brain) level (left) and at neuropil (micro) level (right). In intact brain, incident light is more or less scattered or absorbed by tissue and its contents, with the resulting scattered light detected by an optical system. At the micro level, scattering occurs in distinct elements that include the neuropil (that has its own intrinsic optical signal), and either oxyhemoglobin or deoxyhemoglobin within the blood vessels. Separate absorption and scattering characteristics appear, depending on the relative content of oxyhemoglobin and deoxyhemoglobin. The electromagnetic radiation emitted from the hydrogen dipoles as they reorient from high energy disorganized states to lower energy organized states within the gradient are measured by the detector. Functional MRI (fMRI) uses fast imaging techniques to indirectly detect active neuronal circuits based on relative increases in oxyhemoglobin. This physiological phenomenon results from a local increase in oxygenated blood delivery during neuronal activity. The local increase in oxygenated blood outstrips the gen- eration of deoxyhemoglobin by active tissue, indicating a drop in oxygen extraction by the tissue. The relative decrease in deoxyhemoglobin is detected by blood oxygen level-dependent contrast magnetic resonance imaging (BOLD MRI) “downstream” from the metabolically active tissue. Some studies have compared fMRI directly to cortical electrical stimulation mapping (ESM) performed via open craniotomy or grid stimulation for motor, somatosensory, and language mapping and have demonstrated a correlation between the two methods. For example, compared to sites identified by ESM, sites of increased activity on fMRI are con- siderably larger. The radial cortical projections of subsurface fMRI signals used to create functional cortical maps for computer-assisted surgical navigation may not correspond to cortical surface ESM-identified sites. In its current state of development, fMRI should be used only as an adjunct to ESM for functional mapping. Regarding its ability to predict postoperative deficits, one study of sensorimotor cortex in patients undergoing lesion resections demonstrated a correlation between the size of the margin between the lesion (not the resection margin) and area of fMRI activation and the presence of postoperative neurological deficits. Although many studies show promising results, no consensus has yet been reached about which language tasks best correlate with language measures used during IAP or methods of image acquisition and data analysis. The photon detectors often consist of bismuth germinate or scintillators coupled to photo- multiplier tubes to convert the photons into an electrical signal. PET can be used to detect neuronal activity based on metabolically dependent increased glucose utilization or associated increases in regional cerebral blood flow. The increase in metabolism is detected by fluoro-deoxyglucose (FDG-PET) and blood flow changes are detected by 15O water PET. As with fMRI, studies have shown that compared to essential language sites identified by ESM, sites of language- associated increased PET activity are considerably larger and they may identify language sites where ESM does not disrupt language. Depending upon which tasks are combined to produce activation maps and the method of statistical analysis, PET may fail to identify essential language cortex. Although PET seems inaccurate and unreliable for language localization, it may be adequate for language lateralization. When PET was directly compared to IAP, a study demonstrated a positive predictive value for language lateralization in 80 to 91% of patients, depending on the method of image analysis. Compared to PET, the spatial resolution of SPECT is inferior, but it provides a convenient method of assessing regional cerebral perfusion.

The circuit from cortex to putamen buy 4mg doxazosin amex gastritis symptoms mayo clinic, pallidum purchase doxazosin 2mg free shipping diffuse gastritis definition, STN, substantia nigra pars reticulata, back to thalamus, and then to the cortex, is clearly involved in motor control. The circuit has an inhibitory effect upon the motor thalamus leading to the theory that the circuit tunes in certain desired actions while suppressing undesired actions. In addition, the lack of GPi inhibition of the STN leads to overexcitation of the GPi, particularly because cortical excitatory input to the STN is preserved. This model of basal ganglia function suggests that GPi lesions may improve parkinsonian symp- toms and thalamic lesions should not. However, thalamic lesions help reduce par- kinsonian tremors, suggesting that this model may be incomplete. Cerebellar outputs project to the lateral and posterolateral thalamic nuclei that, in turn, project upon the primary motor cortex. In functional MRI studies comparing real and imagined motions, the cortex and basal ganglia are active in both situations; whereas the cerebellum is only active during real motion. Many physiological studies suggest that the cerebellum stores motor learning for sequential actions and serves to compare the stored plan for intended movement with the proprioceptive evidence of actual movement. If an error or deviation from the desired action occurs, the cerebellum is proposed to help to restore the intended path by modulating the activity of the motor thalamus. Hence, cerebel- lar dysfunction is associated with ataxic movement, decomposition of movement into single-joint components, and reduced correction of movement errors. The neurotransmitters involved (glutamate and gamma aminobuteric acid or GABA) are highly nonspecific and serve the entire CNS. The motor cortex (particularly M1) has major direct efferents that project to multiple brainstem and spinal cord nuclei. The red nucleus gives rise to the rubrospinal pathway, the reticular nuclei of the pons and midbrain give rise to the reticulospinal pathway, and the lateral vestibular nucleus gives rise to the © 2005 by CRC Press LLC vestibulospinal pathway. Such posturing is believed to result from unbalanced brainstem nuclei inputs to the spinal cord, without sculpting and control by the cortex. Lesions of the cortex, basal ganglia, or thalamus result in maintained extremity movement and reduce volitional movement. It appears, therefore, that the brainstem is critical to the maintenance of unconsciously maintained antigrav- ity tone. Due to complex interactions with the brainstem, abnormalities of axial move- ment such as dystonia, are more resistant to treatment. However, considerable further research is required to assess whether direct interventions in brainstem areas might prove more effective for the control of axial movement. For example, beginning in 1932, Bucy per- formed subpial resections of the precentral cortex for the treatment of choreoathetosis and tremor. In 1939, Meyer performed a transventricular ablation of the caudate head and body to treat a patient with parkinsonian tremor. Later, Cooper, in attempt- ing to perform a mesencephalic pedunculotomy for parkinsonian tremor, inadvert- ently tore the anterior choroidal artery. This led to the discovery that ablation of the medial globus pallidus could relieve parkinsonian tremor. Lesions were produced through freezing with liquid nitrogen cryoprobes or thorough heating with microwave radio frequency probes. Until the early 1950s, the globus pallidus was the stereotactic target of choice for the treatment of parkinsonian tremor. In 1954, Hassler and Riechert reported dramatic improvement of parkinsonian tremor © 2005 by CRC Press LLC following placement of a lesion in the ventrolateral thalamus. Until the early 1990s, the primary surgery performed for any type of movement disorder was thalamotomy, the placement of a lesion in the motor thalamus. Eventually these patients were studied as a group, sparking a resurgence of pallidal stereotactic surgery in the 1990s. Although some lesion placement is guided by changes in tissue impedance or the effect of transiently cooling tissue, most surgeons monitor involuntary movements, paresthesias, and tremor suppression resulting from transient electrical stimulation. Radiofrequency lesions carry a risk of hemorrhage, particu- larly in patients with preexisting hypertension where damage to the vessels of the basal ganglia and thalamus may exist prior to surgery. Leksell reported that stereotactically placed lesions in the posteroventral pallidum produced good long-term mitigation of tremor, bradykinesia, and rigidity in 19 of 20 parkinsonian patients (95%) followed for 1 to 5 years. Adverse effects included central homonymous visual field deficits in six patients and transient facial weakness and dysphasia in one patient. In a study of subthalamotomy, only one in 21 patients experienced unmanageable dyskinesias after surgery and proceeded to DBS placement.

Situa- tions that predispose a patient to malnutrition include recent and continuing nausea generic doxazosin 1mg otc gastritis diet , vomit- ing buy doxazosin 2mg without a prescription diet lambung gastritis, diarrhea, inability to feed oneself, inadequate food intake (cancer-related, others), decreased nutrient absorption or utilization, and increased nutrient losses and nutritional re- quirements. If needed, detailed nutritional assessment may be needed for some patients and is discussed in the following section. Although many patients are admitted to the hospital in a nutritionally depleted state, some patients become malnourished during their hospital stay. According to guidelines from the American Society for Parenteral and Enteral Nutrition, “patients should be considered malnourished or at risk of developing malnutrition if they have inadequate nutrient intake for 7 days or more or if they have a weight loss of 10% or more of their preillness body weight. Anthropometric evaluations include comparisons of actual body weight to ideal and usual body weight. Other anthropometric measurements, such as MAMC and TCF, have much 205 Copyright 2002 The McGraw-Hill Companies, Inc. Absolute lymphocyte count is sometimes used as a marker of visceral proteins and im- munocompetence. Visceral protein markers, such as prealbumin and transferrin, may be helpful in evaluating nutritional insult as well as catabolic stress. Although the most com- monly quoted laboratory parameter of nutritional status is albumin, the albumin concentration often reflects hydration status and metabolic response to injury (ie, the acute phase response) more than the nutritional state of the patient, especially in patients with intravascular volume deficits. Preal- bumin is superior as an indicator of malnutrition only because of its shorter half-life. Use of these serum proteins as indicators of malnutrition is subject to the same limitation, however, because they are all affected by catabolic stress. Patients can generally be classified as mildly, moderately, or severely nutritionally depleted based on these parameters. Caloric needs can be determined by one of two means: the Harris–Benedict BEE and the “rule of thumb” method. Total energy requirements = BEE ×Activity factor × Stress factor Use the following correction factors: Activity Level Correction Factor Bedridden 1. T h u s i s m o r e s e n s i t i v e i n d i c a t o r 1 0 – 1 5 m g / d L M i l d d e p l e t i o n o f a c u t e c h a n g e i n n u t r i t i o n a l s t a t u s t h a n i s 5 – 1 0 m g / d L M o d e r a t e d e p l e t i o n a l b u m i n o r T F N < 5 m g / d L S e v e r e d e p l e t i o n N o t r o u t i n e l y a v a i l a b l e L e v e l s a r e q u i c k l y d e p l e t e d a f t e r t r a u m a o r a c u t e i n f e c t i o n. A l s o d e c r e a s e d i n r e s p o n s e t o c i r r h o s i s, h e p a t i t i s, a n d d i a l y s i s, a n d t h e r e - f o r e, s h o u l d b e i n t e r p r e t e d w i t h c a u t i o n A b s o l u t e l y m p h o c y t e c o u n t 1 4 0 0 – 2 0 0 0 M i l d d e p l e t i o n M a y n o t b e v a l i d i n c a n c e r p a t i e n t s. DETERMINING THE ROUTE OF NUTRITIONAL SUPPORT Once nutritional support is indicated, the route for administration is chosen. Enteral supple- mentation by mouth or tube and parenteral nutrition are the main routes for providing nutri- tional support. Enteral Supplementation and Tube Feeding 11 Enteral nutrition encompasses both supplementation by mouth and feeding by tube into the GI tract. In addition, patients who have a functioning GI tract but for whom oral nutrition intake is contraindicated should be consid- ered for tube feedings. If the GI tract is functioning and can be used safely, tube feedings should be ordered in- stead of parenteral nutrition when nutrition support is necessary because it • Is more easily absorbed physiologically • Is associated with fewer complications than TPN • Maintains the gut barrier to infection • Maintains the integrity of the GI tract • Is more cost-effective than TPN • Contraindications to tube feeding can be found in Table 11–3. Parenteral Nutrition Parenteral nutrition usually offers no advantage to the patient with a functioning GI tract. Some patients, because of their disease states, cannot be fed enterally and require par- enteral feedings. When enteral feedings are started, it is often important to assess gastric residual volumes. The small-bore tubes do not allow for aspiration of residual volumes, however, which may be significant if gastric emptying is questionable. Thus, larger bore tubes are often used to start, and, once feeding tolerance is ensured, the tube is changed to a small-bore tube, which can be left in place comfortably for prolonged periods. Feeding di- rectly into the stomach (as opposed to the bowel) is often preferable because the stomach is the best line of defense against hyperosmolarity. Patients at risk for aspiration require longer tubes into the jejunum or duodenum. Types of feeding tubes and placement procedures are discussed in detail in Chapter 13, page 272. Patients with tumors, GI obstruc- tion, adhesions, or abnormal anatomy, however, may require open surgical placement.

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