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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24 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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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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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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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 ) it "spikes": That is, it actively propagates a signal. I have two related ...
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143 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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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 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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What affects the excitable cell membrane threshold?

What are the factors that affect a cell's membrane threshold? What I think is that it's the nature of voltage-gated sodium channels. But it's said that the density of these channels and the diameter ...
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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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Which role do dendritic spikes play in long-term potentation?

In the Wikipedia article on long-term potentiation one reads: »When weak stimuli are applied to many pathways that converge on a single patch of postsynaptic membrane, the individual postsynaptic ...
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28 views

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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42 views

Factors behind frequency of action potential

I understand that the amplitude of an action potential is not influenced by the strength of the stimulus. I also understand that the perception of the strength of the stimulus depends on the frequency ...
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251 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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175 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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44 views

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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263 views

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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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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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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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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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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99 views

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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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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85 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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2answers
274 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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216 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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464 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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54 views

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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397 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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222 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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60 views

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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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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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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340 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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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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2k views

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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3k views

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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780 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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554 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? ...