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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55 views

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

Some books show the resting potential of neurons as -65mV, such as Neuroscience: Exploring the Brain, Fourth Edition (2016, published by Wolters Kluwer). However, a majority of internet sites, ...
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Why is there a notch in the Na curve for an action potential?

Just out of curiosity, why does the Na curve dip down like in the figure below? I can't seem to find an explanation!
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Why does increasing the space constant increase conduction velocity in myelinated neurons if nodes of Ranvier are constantly spaced?

If depolarisation at one node of Ranvier triggers, by passive conduction, an action potential at the next node of Ranvier, why does increasing the space constant increase conduction velocity? Surely ...
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398 views

Myelination and time constant

In textbooks, it says that myelination doesn't really affect the time constant as tau=RC where R is the membrane resistance and C is the membrane capacitance. Myelin increases membrane resistance ...
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Do factors other than concentration gradient and membrane permeability affect the diffusion potential?

If, hypothetically, the concentration gradients and the permeability of 2 different ions (Na+ and K+ for example) in 2 separate solutions are the same, will the diffusion potentials be different? I'm ...
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Bundle of His and Atrioventricular Bundle difference

I see most definition using Bundle of His and AV bundle interchangeable including the wikipedia when you do a Google search for AV bundle But my text book treats as two different things. The action ...
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What is happening at the electrode interface when the electrical field is modified due to the change of ion concentration after an AP?

I have been working for quite a while now on electrophysiology and electrode fabrication. I studied what is happening at the neuron level during an action potential (polarization/depolarization, ...
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Definition of synaptic strength

The canonical definition of action potentials found in textbooks states that action potentials are all alike in shape. From techniques such as spike sorting which are used to attribute ...
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Can below-threshold potential changes of neurons convey information?

In neuroscience we learn that when the membrane potential of a neuron reaches a threshold (typically around -55mV) it "spikes": That is, it actively propagates a signal. I have two related ...
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How do I stimulate a neuron extracellularly, specifically the sphenopalatine ganglion

Apologies if this is too basic of a question, but I am an electrical engineer, just getting into neuromodulation/neurostimulation. For my senior project, I am trying to make a device that stimulates ...
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32 views

Does electrotonic spread/conduction occur in saltatory conduction?

Even as textbooks, and almost all web pages I've seen so far, explain electrotonic spread/conduction as the passive current flow along an axon, they do so with continuous conduction only. Apart from ...
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How does increasing the temperature increase the compound action potential in some nerve cell?

In majority of nerve cells, action potential decreases with an increase in temperature.But a couple of papers I have looked at say some nerve behave in the opposite manner (https://pubmed.ncbi.nlm.nih....
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271 views

Why do ion leak channels exist?

I've recently learned about ion leak channels in the context of membrane potential and action potentials. Neurons have ion pumps that require energy in order to maintain the resting membrane potential ...
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Na+ / K+ ATPase: How does it restore resting membrane potential? [duplicate]

Could not find any sources talking about this (in a clear manner). If the Na+ / K+ ATPase pumps 3 Na+ out for every 2 K+ it pumps in, thus making the cell more negative, why is the Na+ / K+ ATPase ...
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Can Two Opposite Running Action Potential Cross Each Other without Annihilation in One Axon

Can two opposite travelling action potential cross each other annihilation 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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755 views

What recovers normal polarisation after hyperpolarisation?

I have been taught that a $\ce{Na+/~K+}$ pump helps to recover normal polarisation after-hyperpolarisation in neurones. I could not find out how it does that, since I've also been taught that such a ...
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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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Doubt related to nerve impulse transmission

Naturally, the extracellular fluid has more sodium ions and the axoplasm has more potassium ions. Since there are more potassium leakage channels than sodium leakage channels on axoplasm, it is more ...
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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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Action potential: why called “depolarization” when polarity is reversed, not removed?

During an action potential, the voltage shifts from the resting potential of -70 mV, to +30 mV, to then fall return back to the resting potential again of -70 mV. This reverse of the polarity, what ...
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What does myelin insulate against, exactly?

I am aware of the saltatory conduction model, nodes of Ranvier and all that, and that myelin lets electrical signals "jump". What does not add up to me entirely is what the myelin sheath insulates ...
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How would blocking Na/K ATPase affect the ability of a neuron to exhibit a series of action potentials?

Neural firing usually occurs in the form of spike series. Several action potentials are happening in a quick succession. Whereas Na/K pumps (and other pumps) restore ion gradients to allow processes ...
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2answers
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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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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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Physiology of hyperpolarization

In my textbook, it is stated that after the closure of potassium voltage-gated channels and during hyperpolarization, potassium leakage channels allow potassium influx passively and this returns the ...
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433 views

What causes sodium channels to open?

What triggers the opening of sodium channels in a neuronal membrane? Is it acetylcholine that activates sodium channels in the postsynaptic membrane? Are sodium channels like receptors that have to ...
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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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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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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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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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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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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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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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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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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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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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91 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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Could an action potential produce few or more neurotransmitters based on the stimulus received?

I reckon that if you would be able to widen the AP width, it would produce more neurotransmitters in that larger time interval. Is that correct? Or does the neuron have a standard amount of ...
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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 does the membrane of a neuron not stay at its depolarized state?

When an action potential is transmitted along the axon, the membrane reaches its depolarized state by opening Na+ channels. Both K+ (potassium) and Na+ (sodium) are now on both sides with close to ...
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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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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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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 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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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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181 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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236 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 ...