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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Doubt with Sodium and Pottasium pump

The resting membrane potential is maintained by, ·Selective permeability of the plasma membrane to K+ and Na+ ions- There are potassium channels and sodium channels, which are membrane bound ...
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What makes synaptic vesicle release probabilistic?

The fusion of synaptic vesicles (SVs) with the plasma membrane of the active zone (AZ) upon arrival of an action potential (AP) at the presynaptic compartment is a tightly regulated probabilistic ...
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Relationship between membrane current and voltage in neurons

Depolarization of neurons leads currents of different magnitudes flow in or out of the cell, and the Sodium and Potassium currents can be separately plotted (Purves): Caption: Relationship between ...
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Changes of permeability and driving force during voltage clamp

An action potential can be understood in terms of voltage changes, and these are fundamentally a function of relative permeability changes, mostly for Sodium and Potassium ions. If for instance the ...
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How long does it take the neurotransmitters to diffuse accross the synaptic cleft?

Neurotransmitters get from the pre-synaptic neuron to the receptors on the post-synaptic neuron by diffusion across the gap between these two (the synaptic cleft). My question is, how much time does ...
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What material fills the synaptic cleft? Is it water?

The synaptic cleft is the gap between the pre-synaptic and post-synaptic neurons, and neurotransmitters are transferred between the neurons within this region. What substance exits in this space, is ...
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Why does an increase in extracellular Sodium concentration increases action potential amplitude?

The title says it - I wonder why an increase in extracellular Sodium (Na+) concentration increases action potential amplitude? What I understand: I understand that an influx of positively charged Na+...
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The role of voltage-gated ion channels in chemical synapses

I am trying to understand the mechanisms underlying action potential generation on the cellular level. Typically, there is an emphasis on voltage-dependent permeability changes of Potassium (K+) and ...
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28 views

What trajectory do action potentials take, from initial visual stimulus all the way to motor function?

Say we see a mosquito, and our brain tells us 'hey that's a mosquito, you should kill it.' Then we move our hands and slap/clap it. The initial visual stimulus is translated to an action potential ...
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Where does this equation in the electrophysiology literature form come from?

In my studies I keep coming across the form of an equation that is used in many different mathematical models for voltage gated ion channels. The most general form I have found is in the 1977 paper ...
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32 views

What is the correct value of Neuronal Resting Potential,is it -65mV or -70mV

Some Books are showing the resting potential of neurons as -65mV Eg : NEUROSCIENCE-EXPLORING THE BRAIN,Fourth Edition,2016,Wolters Kluwer while Majority of internet sites(including Wikipedia) are ...
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44 views

How does (action potential) hyper-polarisation work?

I understand that after depolarisation, repolarisation and then hyperpolarisaiton occurs and that an area in hyperpolarisation is in its "refractory period". Why does this prevent Na+ ions diffusing "...
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What happens when too much sodium flows in the cell due to a faulty voltage-gated sensor? What about too little?

The activation gate opens, signaling depolarization. Eventually, the inactivation gate closes, ending depolarization and beginning repolarization. What is the physiological impact of the inactivation ...
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52 views

Depolarisation of post synaptic neuron

When the post synaptic neuron begins to depolarise as positive sodium ions move into it and it reaches threshold- does the inside of the neuron actually switch to being more positive than the outside? ...
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81 views

Neuronal membrane resting potential for large cells

I'm reading Medical Physiology by Boron and Boulpaep (a really terrific book). In the chapter Electrophysiology of the Cell Membrane, section Membrane Potential Is Generated by Ion Gradients, Not ...
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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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142 views

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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167 views

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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196 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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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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314 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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191 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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168 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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317 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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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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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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109 views

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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2k 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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752 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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522 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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109 views

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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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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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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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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278 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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186 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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373 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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556 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/...