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Questions tagged [action-potential]

A rapid change in the membrane potential of excitable cells such as neurons and muscles; this usually involves a steep rise (depolarization) followed by a steep fall in membrane potential (repolarization). The cell subsequently enters a short refractory period (hyperpolarized state) during which it cannot generate another action potential.

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Understanding the derivation of the Nernst equation

I am trying to understand how the Nernst equation can be derived and am mostly referring to the explanation given in the book Theoretical Neuroscience by Dayan and Abbott. Given we have a ...
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Why is the resting membrane potential of excitable tissue not affected by the extracellular sodium concentration?

I know that the resting membrane potential for excitable tissue (eg, nerve) is primarily determined by the electronegative difference between the inside and the outside of the membrane for potassium ...
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Why does resting potential not become continually more negative?

(Firstly, I know this is similar to other questions, but I have read those answers and they do not really cover this topic). My understanding of resting potential: action potential is not being ...
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107 views

What makes the electrical charge inside the neuron more positive at the end of action potential and returns it to resting potential?

When a neuron's stimulated by something, electric potential difference changes immediately and inside of the neuron, becomes more potentially positive than the outside of it. I've read that sodium-...
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stabilization mechanism

I am trying to simulate a soma with sealed end in both side and injected current in the middle of the soma. I used Na K and Ca voltage gated channels to get a concentration inside soma. I got a result ...
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How are presynaptic burst firing signals transmitted post-synaptically?

Neurons can exhibit burst firing and this presynaptic process basically results in a flurry of action potentials being fired in a short time window. I'm, however, wondering how these signals are ...
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241 views

Why does decreasing ion channel density result in an action potential not firing?

I'm pretty confused, when i run a simulation of an action potential reducing the sodium and potassium channel densities gradually over time results in an action potential not being fired, and when i ...
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164 views

Understanding Hodgkin-Huxley's model and activation variables

This question is about the Hodgkin-Huxley model as introduced in Eugene M. Izhikevich, Dynamical Systems in Neuroscience, p.33 ff. I'm having trouble to understand and interpret the differential ...
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Functional role of the myelin sheath [duplicate]

One usually reads that the functional role of the myelin sheath is being a good insulator, accelerating the speed of action potential propagation along the myelinated axon. I tried to understand this ...
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159 views

How do firing patterns arise from the activity of many ion channels?

In his answer to another question, Bryan Krause says: Ion channels don't exhibit any firing patterns: neurons exhibit firing patterns that depend on all the channels present [...]. I understand ...
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Can there be multiple EPSPs with constant current injection to a neuron?

I am performing a current clamp experiment and measuring the change in membrane potential of a neuron with different current injections. A constant current of 50pA is injected to the neuron for 100ms. ...
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179 views

why do sodium channels close with excessive extracellular potassium ions in cardiac myocytes?

When there is an excessive concentration of potassium ions outside cardiac myocytes, the membrane potential surely goes up. I would have thought that this would make it easier for the membrane ...
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77 views

How is Na concentration re-established after action potential

I understand that the repolarization is because some K+ chanels are opened with the action potential. But whats happens with the sodium chemical gradient that is needed for a new action potential? Are ...
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In the QRS complex, what does each wave represent?

The QRS complex is a graphical representation of electrical activity of ventricular depolarization. What does each wave (Q, R, S) mean? I read that Q wave means septal depolarization in ventricles. I ...
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Why is extracellular measurement of action potentials so different from intracellular?

I had read in a paper that present a low noise amplifier the following: "...This level of input signal is larger than both typical action potentials (<500μV) and local field potentials (<5 mV). ...
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Why repolarization in ventricles start in last area which is depolarized “epicardium ” rather than first area “endocardium” [closed]

About ventricular repolarization , l know it start in the last area which is depolarized ( that is why it has positive deflection on ECG ) but the question is why it start in that area ( epicardium ) ...
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Can we have the action potential an AC current?

As well known brain are connected to our body by neuronal cells. it transmits and receives its data by action potential during neuronal cells. i wonder if any one can explain to me the properties of ...
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1k views

How greater magnitude implies greater frequency of action potential?

Greater the magnitude of receptor potential, greater is the rate of discharge of action potentials in the nerve fibre.1 Now consider a case where stimulus ( strength ) is large , so there is more ...
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Why nerve fibre is infatiguable?( is my conjecture correct?)

According to this: A nerve fibre cannot be fatigued, even if it is stimulated for a long time. This property of infatiguability is due to absolute refractory period. How is refractory period ...
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What are negative and positive after potentials?

After depolarization: is the slow repolarization phase which follows a rapid fall in spike potential and extends up to attainment of the RMP level. It is called phase of negative after potential and ...
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515 views

Purpose of K+ channels in action potential

I understand that they serve to repolarize the neuron after the Na+ influx. What I don't understand is why this is important. Meaning, let's say all the K+ channels disappeared. So now the ...
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268 views

Why summation takes place at Initial segment?

I know that many EPSPs summate at initial segment to produce action potential. But I don't understand why if EPSP can travel from dendrite to initial segment, then why it doesn't travel further? ...
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How does entry of Ca²⁺ to the myocardiocyte make it more contractible?

I'm trying to understand why an increase of Ca2+ entering into the cell, increases the force of the heart contractions. Based on what I have watched in many lectures videos on Youtube (this one- "...
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Accumulation of Na⁺ and Ca²⁺ in the myocardiocytes while having acute heart failure

Why is it necessary to have accumulation of sodium and calcium ions in the myocardium cells while having acute heart failure? Normally, at resting membrane potential, sodium and calcium are more ...
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1answer
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What does the word “refractory” in “refractory period” refer to? [closed]

What does the word "refractory" in "refractory period" refer to? I know what it means "refractory period" (both, absolute and relative) in the action potential graph, but I don't understand what the ...
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Stimulating an axon causes impulses to travel both ways?

A diagram is presented as such above. The question given states What would be the effect of stimulation to cause a nerve impulse with a microelectrode at the middle of the axon? I thought the nerve ...
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About cell membrane; action potential and resting potential [closed]

Ion X is negatively charged and more concentrated inside than outside the membrane potential of a cell therefore Ex (equilibrium) is positive. Ion X is unknown. Why is the equilibrium positive?
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Elements that make action potential to conduct quicker? [duplicate]

The texts, online materials describe the velocity of conduction of action potential depends on axon's length and cross sectional area e.g. short length and large diameter decreases the resistance. ...
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Movement of few ion during changes in membrane potential

My question is very simple: why is it sufficient for a very few ions (such as 1 in 100000 K+) to move across the membrane to generate a remarkable variation in the membrane potential (like a change of ...
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1answer
784 views

Are Na+/K+ active pumps and K+/Na+ “Leak” channels same as given in the figure?

Na+/K+ channels maintain the resting potential with other sodium and potassium channels. Then what are these "Leak" channels? are they the same Na+/K+ pump in a special condition? If so, what is it? ...
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What is the derivation of the rules of proportionality between axon conduction velocity and diameter?

We have been told that in myelinated fibres, conduction velocity is proportional to the diameter of the axon. In unmyelinated fibres, velocity is proportional to the square root of the diameter. Can ...
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2k views

Why does an electric shock contract the muscle?

From what I understand, the electrical impulse in our nerve cells is not made of electrons, but of ions that move from different environments with different concentrations, which is totally not ...
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164 views

What is the mechanism by which myelination reduces the capacitance of the axon membrane?

There are two mechanisms that have been proposed to me. 1) Layering of Schwann cell membrane with conducting fluid between the layers is analogous to several capacitors in series. Since capacitance ...
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225 views

Do Schwann cells have Na+/K+ ATPase pump? [closed]

I was studying "Action Potential" and this question crossed my mind. Another question is that, "Why does the action potential not occur in Schwann cells, or if it does, how does it occur?" I know that ...
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163 views

Do action potentials cause the neuron to heat up as well as its environment?

I have read that we might be yawning to cool our brains down, so then a thought occurred to me. If we need to cool down our brain, then our brain but heat up for some reason. The only reason I could ...
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274 views

Inward rectifying potassium channels during undershoot of action potential

My professor said that inward rectifying channels help move the membrane potential back to the resting potential during the undershoot phase of the action potential. The membrane potential would have ...
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503 views

Can There Be Two Simultaneous Opposite Running Action Potential in One Axon

Can two action potential travel in the opposite directions simultaneous in an axon? My answer would be affirmative. If the propagation mechanism is linear as described by https://en.wikipedia.org/...
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242 views

How does stimulus reach neural threshold?

I understand that when the stimulus into a neuron is greater than the threshold it triggers the action potential. Do all the contributing stimulus have to occur at the same time, or can they occur ...
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FitzHugh–Nagumo system with diffusion

I was studying the FitzHugh-Nagumo model with diffusion and I quite do not understand the meaning of it. If we consider the system without diffusion, \begin{equation}\label{FHN}\begin{cases} \dot{u}=...
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How does a higher channel density increase speed of propagation of an Action Potential?

If there is a higher density of sodium channels then there will more Na$^+$ flux in the cell. So it's like trying to pass more material through a pipe and therefore the speed of action potential (AP) ...
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820 views

Why is active transport needed in repolarization?

During the repolarization phase of an action potential, the potassium ions diffuse out of the cell, and active transport begins. What I do not understand is why active transport is needed when the ...
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128 views

Concentration gradients across membranes with different ions

I'm trying to gain an intuition for the dynamics of across neuronal membranes. The overarching idea here is they are controlled by ion concentration gradients across the membrane (which we can ...
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Amount of Na+ needed to be transfered in order to depolarize the membrane?

I found out that the number of $Na^+$ ions that is needed to be transfered across the membrane to make it depolarized is a small number. In what way its proved? (Goldman equation maybe?)
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Original paper about the all or none law for neurons

I am looking for the original paper about the all or none law for neural activity. I know that there is a very old article about the all or none law for mammalian heart muscle fibers, but I'm ...
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Average Beginning of Action Potential in ECG by t-f HRV

I have some ECG data where I am estimating the average beginning of the action potential. I am interested in the discrete Fourier analysis of joint t-f HRV when input data is ECG. Frequency domain ...
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Membrane conductance in phase 1 of the cardiac action potential

Correct me if I am wrong, but in phase 1 of the cardiac action potential (for ventricle cells) there is flow of potassium ions due to the opening of transdent potassium channels. To me this would ...
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At what point during an action potential are the sodium potassium pumps working?

I'm trying to understand how all of the potentials during an action potential are created. My question specifically is about the sodium potassium pumps, however I would also be grateful if someone ...
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1answer
441 views

Dendrodendritic synapse through axodendritic synapse at same dendrite?

Reading Wikipedia's article of dendrodendritic synapse, I find that: Dendrodendritic synapses are activated in a similar fashion to axodendritic synapses in respects to using a chemical synapse. ...
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How does an increased amplitude affect nerve conduction velocity?

My professor said that increasing the amplitude (the amount of depolarization e.g. depolarizing from -80 mV instead of -50 mV) leads to a greater conduction velocity.
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538 views

If a blocker prevents repolarization, will the neuron be stuck in a depolarized state forever?

Potassium channels help to repolarize the cell after depolarization. But if the potassium channels are blocked, potassium ions cannot flow out of the cell to increase the membrane potential. Thus, one ...