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 Diffusion 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 ... 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 jstor 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 ratio of a Raman .... Under Placzek s polarizability approximation, it is known that the depolarization ratio of a totally ... 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 intensity of the parallel ... more details
involves changes in diastolic depolarization and the pacemaker current. J Mol Cell Cardiol. Jul 43 1 ... participate to the generation of the diastolic depolarization via a process involving the Na Ca exchanger. References Reflist See also funny current DEFAULTSORT Diastolic Depolarization Category ... 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 .... 29 3 717 27 Kreitzer AC, Regehr WG. 2001b Cerebellar depolarization induced suppression of inhibition ... N, Zimmer A, Kano M. 2002 Presynaptic cannabinoid sensitivity is a major determinant of depolarization ... Purkinje cells modulation by postsynaptic depolarization. J. Physiol. London 456, p. 453 471. Wilson ... more details
Unreferenced date December 2009 Myogenic contraction refers to a Muscle contraction contraction initiated by the myocyte cell itself instead of 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 lead to the initiation of excitation contraction coupling and thus Muscl ... more details
Orphan date April 2012 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
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
Refimprove date December 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. 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 criterion to diagnose left ventricular hypertrophy . ref The Complete Guide to ECGs 2009 ref References 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
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 Vapour phase decomposition , a method used in the semiconductor industry disambig de VPD ... more details
In electrocardiography , 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 Cardiac electrophysiology ... more details
into the cell. The positively charged ions entering the cell cause the depolarization characteristic of an action potential. After depolarization, there s a brief repolarization that takes place with the eflux of potassium through fast acting potassium channels. Like skeletal muscle, depolarization ... is 0.19 seconds. Microscopically, the wave of depolarization propagates to adjacent cells via .... This property allows rapid, synchronous depolarization of the myocardium. While normally advantageous ... then no longer participate in synchronous myocardial contractility . Depolarization and the ECG Image ... is shorter and broader than the right, impulses reach the erection muscles just prior to depolarization .... The spread of electrical activity depolarization through the ventricular myocardium produces the QRS ... depolarization of the right and left atria QRS complex right and left ventricular depolarization ... interval time interval from onset of atrial depolarization P wave to onset of ventricular depolarization QRS complex QRS duration duration of ventricular muscle depolarization QT interval duration of ventricular depolarization and repolarization RR interval duration of ventricular cardiac cycle an indicator ... more details
and this leads to the depolarization of the hair cell. This pattern of depolarization should not be confused with the more common depolarization which involves the influx of Na into the cell ... more Na and less K compared to intracellular matrix . This depolarization will open voltage gated ... when the sterocilia move toward the kinocilium. The depolarization of the hair cell causes neurotransmitter ... more details
Infobox Disease Name Accelerated idioventricular rhythm Image Caption DiseasesDB ICD10 ICD10 I 45 6 i 30 ICD9 ICDO OMIM MedlinePlus eMedicineSubj eMedicineTopic MeshID D016170 In accelerated idioventricular rhythm AIVR , the rate of cardiac contraction is determined by the intrinsic rate of depolarization of the cardiac cells. It can be present at birth. ref name pmid17687587 cite journal author Freire G, Dubrow I title Accelerated idioventricular rhythm in newborns a worrisome but benign entity with or without congenital heart disease journal Pediatr Cardiol volume 29 issue 2 pages 457 62 year 2008 month March pmid 17687587 doi 10.1007 s00246 007 9024 z ref Pathophysiology In normal hearts the sinoatrial node in the atria depolarizes at a rate of 60 100 beats per minute as an effect of the parasympathetic autonomic nervous system otherwise the SA node would depolarize at a rate of 120 beats per minute . This suppresses the intrinsic depolarization of the other parts of the heart. The accelerated idioventricular rhythm occurs when depolarization rate of a normally suppressed focus increases to above that of the higher order focuses the sinoatrial node and the atrioventricular node . This most commonly occurs in the setting of a sinus bradycardia . ref name urlAccelerated Idioventricular Rhythm Overview eMedicine cite web url http www.emedicine.com med topic12.htm title Accelerated Idioventricular Rhythm Overview eMedicine format work accessdate 2008 12 21 ref Accelerated idioventricular rhythm is also the most common reperfusion arrhythmia in humans. However, ventricular tachycardia and ventricular fibrillation remain the most important causes of sudden death following spontaneous restoration of antegrade flow. ref AL Moens, MJ Claeys, JP Timmermans, CJ Vrints. Myocardial ischemia reperfusion injury, a clinical view on a complex pathophysiological process. International Journal of Cardiology 2005 100 179 ref Appearance AIVR appears similar to ventricular tachycardia ... more details
A non noradrenergic, non cholinergic transmitter NANC is a neurotransmitter of the Autonomic Nervous System ANS that is neither of the main two ANS 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
to reach the initiation threshold for a second depolarization. The return to the equilibrium ... consists of three phases. Phase one is depolarization. During depolarization, voltage gated sodium ... is made less negative. After the potential reaches the activation threshold 55 mV , the depolarization ... have two gating mechanisms, the activation mechanism that opens the channel with depolarization ... state, it will not open in response to depolarization. The period when the majority of sodium ... voltage activated sodium channels in the closed active state to respond to depolarization. However, voltage gated potassium channels that opened in response to depolarization do not close ... 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
Infobox Anatomy Name PAGENAME Latin GraySubject GrayPage Image Caption Image2 Caption2 Precursor System Artery Vein Nerve Lymph MeshName MeshNumber Code TerminologiaHistologica 2 00 06.1.00003 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 edition 7th 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 de Axolemm ... 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 the repolarization phase usually returns the membrane potential back to the resting membrane potential . 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 he pl Repolaryzacja fi Repolarisaatio ... more details
Infobox Disease Name Parasystole 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 heart atrium or the Ventricle heart 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 beat s will wander through the basic cycle of the sinus rhythm . Accordingly, the traditional electrocardiographic criteria used to recognize the fixed form of parasystole are the presence of variable coupling intervals of the manifest ectopic beats inter ectopic intervals that are simple multiples of a common denominator fusion beat s. 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 ... more details
wiktionarypar firing Firing most commonly refers to the involuntary termination of employment. Firing may also refer to Operation Operating devices, for example firing the shutter on a camera. The act of starting a fire Shooting , the usage of firearms Execution by firing squad , a method of capital punishment 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 Material Fuel , any material such as firewood that can be burned to release energy. 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
distinguish Dyad for the chemical compound abbreviated DIAD Diisopropyl azodicarboxylate The diad is a structure in the cardiac myocyte located at the sarcomere Z line. It is composed of a single t tubule paired with a terminal cisterna of the sarcoplasmic reticulum . The diad plays an important role in excitation contraction coupling by juxtaposing an inlet for the action potential near a source of Ca sup 2 sup ions. This way, the wave of depolarization can be coupled to calcium mediated cardiac muscle Muscle contraction contraction via the sliding filament mechanism. References cite book author Stanton, Bruce A. Berne, Robert M. Levy, Matthew N. Koeppen, Bruce M. title Physiology publisher Mosby location St. Louis year 2005 pages isbn 0 323 03390 3 oclc doi Category Human cells anatomy stub sr ... more details
Orphan date September 2008 A Lewis Lead also called the S5 lead is a modified EKG lead used to detect atrial flutter waves when atrial flutter is suspected clinically but not definitely demonstrated on the standard 12 lead EKG. In order to create the Lewis Lead, the right arm electrode is moved to the right, second intercostal space adjacent to the Human sternum sternum . Then the left arm electrode is moved to the right, fourth intercostal space adjacent to the sternum. The Lewis Lead is then read as Lead I on the EKG and, since in most patients it will be roughly perpendicular to the wave of atrial depolarization , flutter waves may be more apparent. References Goldman s Principals of Clinical Electrocardiography 1982 Category Cardiology Category Electrodiagnosis Category Cardiac electrophysiology Medicine stub ... more details
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