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When threshold is reached at the SA node what channels open causing further depolarization of the membrane?
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∙ 10y ago
Fast Calcium
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∙ 10y ago
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How would Damaged heart tissue affect mean electrical axis?
damages or disease of the heart could cause changes of the path of depolarization (mean electrical axis). such affects would result in abnormalities in ECG trace. ultimately causing MEA to be off
How does acetylcholine induce a decrease in heart rate?
Yes it does. Acetylcholine decreases the heart rate. It acts on the muscarinic (m2) receptor which decreases the activity of adenylate cyclase. This in turn decreases the production of cycliac AMP -> decreases the amount of protein kinase a activated -> decreases the amount of calcuim entry -> decreased activity of myocytes in heart- which results in decreased permeability of l type voltaged gated calcuim channels and decreases the length of time they are open for -> decreased calcuim levels -> decreased heart rate.
How can sodium channel blockers terminate re-entry in cardiac arrhythmia?
Cardiac arrhythmia is cause by the presence of an ectopic focus or a re-entry mechanism where an action potential is delayed for some reason and enters nearby muscle fibres that are no longer refractory causing depolarisation and establishing a circuit movement. There are three classes of anti-arrhythmic drugs which block sodium channels: Class IA drugs block open Na+ sodium and can increase the effective refractory period. They produce a frequency-dependent block As they dissociate slowly away from these Na+ channels, they can prevent the Na+ channel from contributing towards an action potential if the frequency is high. Disopyramide one such example. It is used to treat ventricular arrhythmia by resulting in a negative inotropic effect. Class IB drugs block closed Na+ sodium. It is often used to treat ventricular arrhythmia after an acute myocardial infraction. Lidocaine is one such example. It has little effect on normal cardiac tissues as it dissociates quickly from the Na+ channels. However, many Na+ channels are closed in ischemic cases due to anoxia. Lidocaine can hence act on these closed Na+ channels. Class IC drugs are the most potent when it comes to blocking Na+ channels. They slowly dissociate from the Na+ channels and it leads to depressed conduction in the myocardium. These agents can prolong the RP and QRS intervals. Flecainide is one such example and it is used the treat atrial fibrillation.
What is responsible for causing accretion?
gravitation
What will happen if Mt Rainier erupts?
Even a relatively small eruption at Mount Rainier could melt the snow and ice at the volcano's summit. This could mix with volcanic ash as well as sediment around the volcano, forming mudflows called lahars. These could potentially devastate nearby towns and even the city of Tacoma. The mud could then clog river channels, causing the rivers to back up and flood portions of Seattle.
What causes rapid depolarization phase of a pacemaker cell?
Rapid depolarization happens after the membrane threshold has been reached and Na+ ions start to flow into the cell. As more Na+ ions flood in the cell becomes more and more positive. This causes the voltage gated Na+ channels to open creating a flood of Na+ ions and thus a rapid phase of depolarization. Shortly after this rapid phase K+ ions are released from the cell causing the cell to become more negative closing the Na+ channels and thus repolarizing the cell.
What is the primary action during depolarization of an action potential?
Sodium ions flow into the neuron via voltage-gated sodium ion channels, driving the membrane potential into the positive. Beyond the threshold, more sodium ion channels are opened, causing the influx of sodium further downstream, and the process repeats, propagating the action potential down the axon.
What ion flows into a nerve cell when an axon's membrane depolarizes?
During the depolarization phase, sodium ions enter the cell through the open ion-channels (Na+ influx).
Describe the action of depolarization and repolarization?
Depolarization is due to the influx of Na+ which causes the cell's internal membrane to become more positive, leading to an action potential. Repolarization occurs when K+ leaves the cell causing the interior of the cell to become negative again.
Which ion channel opens in response to a change in membrane potential and participates in the generation and conduction of action potentials?
Sodium channels. A neuron's membrane potential may depolarize for many reasons (neurotransmitters, mechanical deflection, electrical synapse, etc). When that membrane depolarizes to the point of its threshold of activation, then voltage gated channels open up an allow an influx of sodium into the cell. This rapidly depolarizes the cell's membrane, causing that upward peak or rising phase to occur.
What are the Stages of nerve impulses?
The action potential has 5 main phases:1) stimulation/rising phase - depolarization caused by influx of sodium ions at the axon hillock; potential increases from a resting potential of -70 mV2) peak phase - depolarization and membrane potential reaches a peak, with sodium channels open maximally, at about +40 mV3) falling phase - potassium channels open in response, causing a subsequent reduction in membrane potential, and the neuron begins to repolarize4) hyperpolarization/undershoot phase - more potassium channels stay open after sodium channels close, causing a hyperpolarization of the neuronal membrane, bringing the potential down below its initial resting potential (below -70 mV)5) refractory phase - potassium channels begin to close, allowing the membrane potential to revert back to the resting potential of -70 mV; during this phase, the probability of the nerve being able to refire is extremely low, thus allowing for a delay between action potentials
What ion is the rising phase of the action potential?
Sodium ions are responsible for the rising phase of the action potential. This occurs when sodium channels open and sodium ions flow into the cell, causing depolarization.
What happen to action potential if NA plus concentration increases?
I don't think there is a very large effect unless your plasma sodium concentration is seriously out of whack. Changes in plasma calcium or potassium concentrations can affect action potentials a lot more than changes in sodium. I guess theoretically increased sodium intake will tend to depolarize everything.
What initiates the depolarization of the membrane in muscle contraction?
Muscles contract when they receive nerve signals from the brain, telling them to put filaments in action. The thin ones slide past the thick, shortening the sarcomere (this is a special part of the muscle).
What affect does lowering extracellular calcium have on the resting membrane potential of a neuron?
Low calcium levels in the extracellular fluid increase the permeability of neuronal membranes to sodium ions, causing a progressive depolarization, which increases the possibility of action potentials. These action potentials may be spontaneously generated, causing contraction of skeletal muscles (tetany).
How does an impulse move from one neuron to another?
By a synapse. There are 2 types of synapses.Chemical synapses are more common & function by sending chemicals called neurotransmitters from the pre-synaptic neuron to the post-synaptic neuron. These neurotransmitters affect the post-synaptic neuron by causing ligand gated sodium ion channels to open, causing sodium influx into the cell, and resulting in a change in the membrane voltage potential. This change in membrane voltage potential is called depolarization and is the beginning of an action potential.Electrical synapses have gap junctions between the 2 neurons allowing ionic charge inside the cells to travel quickly between cells.
What ion is released within the myocardial cell with the depolarization and acts on the contractile proteins causing the cell to contract?
myosin?
