Other uses Portal Neuroscience In biology, depolarization is a change in a cell s membrane potential , making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential . Hyperpolarization biology Hyperpolarization is the opposite of depolarization, and inhibits the rise of an action potential. Mechanism If, for example, a cell has a resting potential of 70mV, once the membrane potential changes to 50mV, then the cell has been depolarized. Depolarization is often caused by influx of cation s, e.g. sodium Na sup sup through sodium channel Na sup sup channels , or Calcium Ca sup 2 sup through Calcium channel Ca sup 2 sup channels . On the other hand, efflux of potassium K sup sup through potassium channel K sup sup channels inhibits depolarization, as does influx of chloride Cl sup &ndash sup an anion through chloride channel Cl sup &ndash sup channels . If a cell has K sup sup or Cl sup &ndash sup currents at rest, then inhibition of those currents will also result in a depolarization. Because depolarization is a change in membrane voltage , electrophysiology electrophysiologists measure it using electrophysiology Current clamp current clamp techniques. In voltage clamp , the membrane currents giving rise to depolarization are either an increase in inward current, or a decrease in outward current. Depolarization blockers Depolarization block redirects here There are drugs, called Neuromuscular blocking drugs Depolarizing blocking agents depolarization blocking agents , that inhibit depolarization, e.g. by blocking the channels responsible for depolarization, or by opening K sup sup channels. Examples include the nicotinic agonist s suxamethonium and decamethonium . ref name Rang149 cite book author Rang, H. P. title Pharmacology publisher Churchill Livingstone location Edinburgh year 2003 pages isbn 0 443 07145 4 oclc doi Page 149 ref References Reflist External links http www.ncbi.nlm.nih.gov books ... more details
Depolarization or depolarizer may refer to Depolarization , a decrease in the absolute value of a cell s membrane potential Depolarizer , a substance used to depolarize an electrochemical cell Depolarization ratio , the intensity ratio between the parallel component and the perpendicular component of Raman scattered light Depolarizer optics , a device for randomizing the polarization of light disambig ... more details
Other uses Depolarization disambiguation File Cyclohexane Polarized Raman.JPG right In Raman spectroscopy , the depolarization ratio is the Intensity physics intensity ratio between the perpendicular component and the parallel component of the Raman scattered light. ref name Allemand Charly D. Allemand, Depolarization Ratio Measurements in Raman Spectrometry , Applied Spectroscopy 24 3 , 1970, pp. 348 353 ref Early work in this field was carried out by George Placzek , who developed the theoretical treatment of bond polarizability ref name Long cite journal author D. A. Long title Intensities in Raman Spectra. I. A Bond Polarizability Theory journal Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences volume 217 issue 1129 date Apr. 8, 1953 pages 203 221 url http www.jstor.org stable 99022 ref The Raman scattered light is emitted by the stimulation of the electric field of the incident light. Therefore, the direction of the vibration of the electric field, or Polarization waves polarization direction, of the scattered light might be expected to be the same as that of the incident light. In reality, however, some fraction of the Raman scattered light has a polarization direction that is perpendicular to that of the incident light. This component is called the perpendicular component . Naturally, the component of the Raman scattered light whose polarization direction is parallel to that of the incident light is called the parallel component , and the Raman scattered light consists of the parallel component and the perpendicular component. The ratio between these two components is expressed as the depolarization ratio. The value of the depolarization ... the normal mode belongs. Under Placzek s polarizability approximation, it is known that the depolarization ... equals 0.75. A Raman band whose depolarization ratio is less than 0.75 is called a polarized band , and a band with a 0.75 depolarization ratio is called a depolarized band . The ratio of the peak ... more details
depolarization and the pacemaker current. J Mol Cell Cardiol. Jul 43 1 39 48. ref . There is now ... of the diastolic depolarization via a process involving the Na Ca exchanger. References ... more details
simply by depolarization of the target cell, this phenomenon was termed depolarization induced suppression ... whose synthesis or release was stimulated by the depolarization of the target cell. This messenger ..., Kreitzer s group also discovered that depolarization of Purkinje cells could also cause a temporary ... et al. 2001b . This phenomenon was termed depolarization induced suppression of excitation DSE ... AC, Regehr WG. 2001b Cerebellar depolarization induced suppression of inhibition is mediated ... M. 2002 Presynaptic cannabinoid sensitivity is a major determinant of depolarization induced retrograde ... modulation by postsynaptic depolarization. J. Physiol. London 456, p. 453 471. Wilson RI, Nicoll RA ... more details
Context date June 2009 The Hodgkin cycle represents a positive feedback loop in which an initial membrane depolarization leads to uncontrolled deflection of the membrane potential to near V sub Na sub . The initial depolarization must reach or surpass threshold in order to activate voltage gated Na channels. Opening of Na channels allows Na inflow which, in turn, further depolarizes the membrane. Additional depolarization activates additional Na channels. This cycle leads to a very rapid rise in Na conductance g sub Na sub , which moves the membrane potential close to V sub Na sub . Created by Alan Lloyd Hodgkin . File Hodgkin Cycle.jpg Category Membrane biology ... more details
Unreferenced date December 2009 Myogenic contraction refers to a myocyte Muscle contraction contraction that originates from a property of the myocyte itself, i.e. the contraction is initiated by the cell itself, not an outside occurrence or stimulus such as nerve innervation. Mechanisms Unstable Membrane Potentials Many cell biology cells have resting membrane potential s that are unstable. This instability is usually due to ion channels in the cell membrane that spontaneously open and close e.g. Funny current I sub f sub channels in cardiac pacemaker cells . When the membrane potential reaches Action potential Threshold and initiation depolarization threshold an action potential AP is fired, excitation contraction coupling initiates and the myocyte contracts. Slow wave potentials Slow wave potential are unstable resting membrane potential s that continuously cycle through depolarization and repolarization phases. However, not every cycle reaches Action potential Threshold and initiation depolarization threshold and thus an action potential AP will not always fire. Owing to temporal summation depolarization potentials spaced closely together in time so that they summate , however, cell membrane depolarization will periodically reach Action potential Threshold and initiation depolarization threshold and an action potential will fire, triggering contraction of the myocyte . Pacemaker potentials Pacemaker potential s are unstable resting membrane potential cell membrane potentials that reach Action potential Threshold and initiation depolarization threshold with every depolarization repolarization cycle. This results in action potential AP s being fired according to a set rhythm. Cardiac pacemaker cells, a type of cardiac myocyte in the SA node of heart, are an example of cells with a pacemaker potential . Stretch This mechanism involves the opening of mechanically gated Ca sup 2 sup channels when some myocyte s are stretched. The resulting influx of Ca sup 2 sup ions ... more details
VPD may refer to Vancouver Police Department Virtual private database Vital Product Data , an AIX terminology Virtual Product Development Vapour Pressure Deficit , a measure of the difference between air humidity and saturation Ventricular Premature Depolarization Premature ventricular contraction , PVC , an untimely action of the heart disambig ... more details
Wikify date January 2011 Refimprove date December 2009 Context date October 2009 In the electrocardiogram , the time of the onset of the intrinsicoid deflection , also referred to as the R wave peak time , is measured from the beginning of the QRS complex to the peak of the R wave. The intrinsicoid deflection reflects the depolarization vector from the endocardium to the epicardium. Diagnostic significance In the presence of bundle branch block or ventricular hypertrophy, the depolarization impulse takes a longer than normal period of time to reach the recording electrode. This delays the onset of the intrinsicoid deflection. This prolongation or delay is an important criterion for diagnosing bundle branch block and ventricular hypertrophy. Onset of intrinsicoid deflection 0.05 seconds just over one small box is used as a non voltage related criterium to diagnose left ventricular hypertrophy. ref The Complete Guide to ECGs 2009 ref Reflist DEFAULTSORT Intrinsicoid Deflection Category Cardiac electrophysiology Med stub ... more details
An antidromic impulse in an axon refers to conduction opposite of the normal orthodromic direction Citation needed date July 2010 . That is, it refers to conduction along the axon away from the axon terminal s and towards the soma biology soma . For most neurons, their dendrites , soma biology soma , or axons are depolarization depolarized forming an action potential that moves from the starting point of the depolarization near the cell body along the axons of the neuron. Antidromic activation is usually induced experimentally by direct electrical stimulation of a presumed target structure Clarify date July 2010 . Antidromic activation is usually used to confirm that a neuron being recorded from projects to the structure of interest. See also orthodromic neuron dendrite axon action potential Category Neurophysiology Neuroscience stub pl Przewodzenie antydromowe ... more details
During a cardiac cycle , once an action potential is initiated, there is a period of time that a new action potential cannot be initiated. This is termed the effective refractory period ERP of the tissue. This period is also termed the absolute refractory period ARP . During this period, depolarization on adjacent cardiac muscles does not produce a new depolarization in the current cell as it has to refract back to phase 4 of the action potential before a new action potential can activate it. ERP acts as a protective mechanism and keeps the heart rate in check and prevents arrhythmias and coordinates muscle contraction. Anti arrhytmic agents used for arrhythmias usually prolong the ERP. For the treatment of Atrial fibrillation , it is a problem that the prolongation of the ERP by these agents also affects the ventricles, which can induce other types of arrhythmias. gallery Image ERP.svg myocardial action potential gallery Cardiovascular physiology Category physiology Category Cardiac electrophysiology ... more details
Orphan date January 2007 Cardiac rhythmicity is the spontaneous depolarization and repolarization event that occurs in a repetitive and stable manner within the cardiac muscle. Rhythmicity is often abnormal or lost in cases of cardiac dysfunction or cardiac failure . References PhysioEx 6.0 by Peter Zao Timothy Stabler Greta Peterson Lori Smith references Category Cardiac electrophysiology medicine stub ... more details
to reach the initiation threshold for a second depolarization. The return to the equilibrium ... phases. Phase one is depolarization. During depolarization, voltage gated sodium ion channels ... negative. After the potential reaches the activation threshold 55mV the depolarization is actively ... mechanism that opens the channel with depolarization and the inactivation mechanism that closes ... to depolarization. The period when the majority of sodium channels remain in the inactive state ... in the closed active state to respond to depolarization. However, voltage gated potassium channels that opened in response to depolarization don t close as quickly as voltage gated sodium channels ... more details
Image Action potential vert.png thumb 350px A. A schematic view of an idealized action potential illustrates its various phases as the action potential passes a point on a cell membrane . B. Actual recordings of action potentials are often distorted compared to the schematic view because of variations in electrophysiology electrophysiological techniques used to make the recording. The threshold potential is the membrane potential to which a membrane must be depolarization depolarized to initiate an action potential . It often can be between 40 and 55 volt mV , but it can vary based upon several factors. If ion channel s are available, that will move the potential in the direction of the equilibrium potential for that ion sodium ion channel Na sup sup is approximately 55mV potassium channel K sup sup is approximately 95mV chloride channel Cl sup sup is approximately 90mV Therefore, resting ion channel for sodium will depolarization depolarize and thus excite, while channels for potassium or chloride will hyperpolarization biology hyperpolarize and thus inhibit. External links eMedicineDictionary threshold stimulus GeorgiaPhysiology 1 1ch4 s1ch4 8 http www.cameron.edu gabrielr PHYCH4 sld013.htm Description at cameron.edu http www.ncbi.nlm.nih.gov books bv.fcgi?rid mcb.figgrp.6213 Diagram at nih.gov neuro stub Category Electrophysiology de Schwellenpotential pl Potencja progowy ... more details
The axolemma is the cell membrane surrounding an axon . It is responsible for maintaining the membrane potential of the neuron, and it contains ion channel s through which ions can flow. When this occurs, the voltage inside the axon changes, and depolarization or hyperpolarization of the membrane can occur. Adequate depolarization can lead to an action potential , which travels down the axon in a self propagating manner as more ion channels open due to stimulation by the influx of positive ions. ref name Marieb cite book author Elaine N. Marieb and Katja Hoehn title Human Anatomy & Physiology 7th Ed. publisher Pearson pages 393 412 year 2007 isbn 0 805 35909 5 ref If the axolemma is damaged, it becomes unable to perform its vital role of maintaining the concentration gradient of ions inside and outside of the cell. When ions move down their concentration gradient into the cell, they can cause a number of different cellular processes that may lead to cell damage or Necrosis cell death . References reflist 1 External links eMedicineDictionary Axolemma BUHistology 22802loa Cell biology stub Nervous tissue Category Neurons Category Neuroanatomy ... more details
Unreferenced date December 2009 In neuroscience , repolarization refers to the change in membrane potential that returns the membrane potential to a negative value after the depolarization phase of an action potential has just previously changed the membrane potential to a positive value. Repolarization results from the movement of positively charged potassium ion s out of the cell. Typically the repolarization phase of an action potential results in Hyperpolarization biology hyperpolarization , attainment of a membrane potential that is more negative than the resting potential . See also membrane potential action potential Category Electrophysiology ar de Repolarisation pl Repolaryzacja fi Repolarisaatio ... more details
Infobox Disease Name PAGENAME Image Caption DiseasesDB ICD10 ICD9 ICDO OMIM MedlinePlus eMedicineSubj eMedicineTopic MeshID D017574 Parasystole is a kind of arrhythmia caused by the presence and function of a secondary cardiac pacemaker pacemaker in the heart, which works in parallel with the SA node . Parasystolic pacemakers are protected from depolarization by the SA node by some kind of entrance block . This block can be complete or incomplete. Parasystolic pacemakers can exist in both the atrium or the ventricle. Atrial parasystolia are characterized by narrow QRS complexes Two forms of ventricular parasystole have been described in the literature, fixed parasystole and modulated parasystole. Fixed ventricular parasystole occurs when an ectopic pacemaker is protected by entrance block, and thus its activity is completely independent from the sinus pacemaker activity. Hence, the ectopic pacemaker is expected to fire at a fixed rate. Therefore, on ECG, the coupling intervals of the manifest ectopic beats will wander through the basic cycle of the sinus rhythm. Accordingly, the traditional electrocardiographic criteria used to recognize the fixed form of parasystole are i the presence of variable coupling intervals of the manifest ectopic beats ii inter ectopic intervals that are simple multiples of a common denominator iii fusion beats. According to the modulated parasystole hypothesis, Rigid constancy of a pacemaker might be expected if the entrance block were complete, but if there is an escape route available for the emergence of ectopic activity, then clearly there must be an effective ionic communication, not complete insulation, between the two tissues. If there is an electrical communication between the two, then the depolarization of the surrounding ventricle may influence the ectopic pacemaker. That influence will be electrotonic depolarization of the surrounding field will induce a partial depolarization of the pacemaker cells. Therefore, appropriate dia ... more details
wiktionarypar firing Firing most commonly refers to the involuntary termination of employment. Firing may also refer to Operation Kort Koppmann Operating devices, for example firing the shutter on a camera. The act of starting a fire Pottery firing in a kiln or oven Pin firing , an old medical treatment applied to horses An action potential , where the depolarization of a neuron causes it to fire an electrical signal down its axon Media Fired , a song by Ben Folds from his 2001 debut solo album Rockin the Suburbs Fired a 2007 documentary film by Annabelle Gurwitch Fired film Fired film , a 2010 Indian horror film See also Fire and Fire disambiguation Firing squad disambig ... more details
A secretagogue is a substance that causes another substance to be secreted . One example is gastrin , ref eMedicineDictionary secretagogue ref , which stimulates the H K ATPase in the parietal cell s increased gastric acid production by the stomach . Pentagastrin , a synthetic gastrin, histamine , and acetylcholine are also gastric secretagogues. Sulfonylurea s are insulin secretagogues, triggering insulin release by direct action on the K sub ATP sub channel of the pancreatic beta cell s. Blockage of this channel leads to depolarization and secretion of vesicles. Angiotensin II is a secretagogue for aldosterone from the adrenal gland . References references External links DorlandsDict seven 000095492 Secretagogue Category Endocrinology medicine stub es Secretagogo fr S cr tagogue ... more details
An ionotropic effect is a special kind of effect of a hormone on its target. The hormone activates or deactivates ionotropic receptor s ligand gated ion channels . The effect can be either positive or negative, whether the effect is a depolarization or a hyperpolarization respectively. Examples Noradrenaline aka. Norepinephrine has a positive ionotropic effect on heart muscle , when binding to beta 1 adrenergic receptor s on this tissue. ref name purves Neuroscience Purves , Third Edition, table 20 2 ref The result is an increased cardiac output . References references DEFAULTSORT Ionotropic Effect Category Membrane biology Category Electrophysiology Category Neurochemistry Category Molecular neuroscience ... more details
Summary Information Description I made this plot for Wikipedia based upon the nerve fiber recruitment inversion plot in Grill WM, Mortimer JT 1997 . Inversion of the current distance relationship by transient depolarization . IEEE Transactions on Biomedical Engineering 44 1 1 9. Source I User Guvanasen Guvanasen User talk Guvanasen talk created this work entirely by myself. Date 23 24, 30 November 2009 UTC Author User Guvanasen Guvanasen User talk Guvanasen talk other versions Licensing PD self date November 2009 ... more details
orphan date March 2010 The surfactant albumin ratio is a test for assessing Fetus fetal lung maturity. ref name pmid10920328 cite journal author Liu KZ, Shaw RA, Dembinski TC, Reid GJ, Ying SL, Mantsch HH title Comparison of infrared spectroscopic and fluorescence depolarization assays for fetal lung maturity journal Am. J. Obstet. Gynecol. volume 183 issue 1 pages 181 7 year 2000 month July pmid 10920328 doi 10.1067 mob.2000.105345 url http linkinghub.elsevier.com retrieve pii S0002 9378 00 77338 8 ref References reflist Obstetrical procedures Category Embryology medicine stub ... more details
A non noradrenergic, non cholinergic transmitter NANC is a neurotransmitter of the peripheral nervous system PNS that is neither of the main two PNS transmitters, i.e. noradrenaline and acetylcholine . Comparison table This table compares different NANCs in the PNS class wikitable sortable Neurotransmitter Type Location ref name Rang132 Unless else specified in table, then ref is cite book author Rang, H. P. title Pharmacology publisher Churchill Livingstone location Edinburgh year 2003 pages isbn 0 443 07145 4 oclc doi Page 132 ref Function ref name Rang132 adenosine triphosphate ATP non peptide postganglionic sympathetic neuron s e.g. in blood vessel s & vas deferens Fast depolarization contraction vasoconstriction GABA non peptide enteric nervous system ENS s peristalsis 5 HT non peptide enteric nervous system ENS s peristalsis dopamine non peptide some sympathetic nervous system SNS s e.g. kidney vasodilation nitric oxide NO non peptide pelvic nerve s & gastric nerve s erection gastric emptying neuropeptide Y NPY peptide postganglionic sympathetic neuron s e.g. blood vessel s enhance vasoconstrictor action of noradrenaline noradrenaline release inhibitor vasoactive intestinal peptide VIP peptide parasympathetic nerves to salivary gland s NANC innervation to smooth muscle of airways vasodilation acetylcholine cotransmitter bronchodilation GnRH peptide sympathetic ganglia slow depolarization acetylcholine cotransmitter substance P peptide sympathetic ganglia enteric nervous system ENS s slow depolarization acetylcholine cotransmitter calcitonin gene related peptide CGRP peptide non myelinated sensory neuron s vasodilation increase vascular permeability neurogenic inflammation References references Category Neurotransmitters Category Peripheral nervous system ... more details
block of Na channels and its effect on closing rate Bot generated title ref causes a partial depolarization ... retrieve pii S016752730500269X ref causes a partial depolarization of the resting membrane potential ... causes a partial depolarization of the muscle membrane Ischaemia causes a partial depolarization of the muscle ... Hyperkalemia causes a marked depolarization of the resting membrane potential Hypokalemia hyper polarization ... same as parasympathetic stimulation Marked Hypoxia causes a marked depolarization of the resting ... more details
Encyclopedia
top
