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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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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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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Refractory period in action potential

I know that the part E in this graph is definitely the part of refractory period. My question : Will there be any effect on B,C or D if a stimulus is given at time B,CorD respectively ?
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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 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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What is the effect of extra-cellular potassium concentration on heart rate and conduction velocity?

If the extracellular potassium concentration surrounding a myocyte increases, then the potassium gradient accross the cell membrane decreases, and therefore the resting membrane potential will become ...
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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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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 ...
John Smith's user avatar
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Confused at what is happening with these action potentials

Ok so for a bit of a background, I am doing a science project looking at the action potentials of the earthworm. I anaesthatized the worms then hooked them up to a spiker box (http://backyardbrains....
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Can a single axon propagate multiple simultaneous action potentials?

I have not been able to locate any research that indicates whether a single axon of a neuron or nerve cell can conduct multiple simultaneous (i.e. spatially separate) action potentials. I am aware ...
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How to conceptualize the action potential?

In my AP Biology class, we were taught that action potentials are not electrical impulses in the same way current travels through a wire. Rather, we were taught that action potentials are changing ...
eepperly16's user avatar
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Why does hypercalcemia cause muscle weakness, yet hyperkalemia causes muscle excitation?

The reasoning I've been given is that high extracellular $[K^+]$ increases the $E_v$ of potassium; therefore, membrane potential increases and the threshold for action potentials is more easily ...
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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 ...
Nicholas Hassan's user avatar
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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 ...
BioPhysicist's user avatar
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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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Action potential and sodium channels

In this video on electro tonic potential, the tutor says that when the potassium channels open the potential drops from +40mV to -80mV, where the sodium channels have already closed at +40mV. Now in ...
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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 ...
D.J. Lawson's user avatar
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Hodgkin huxley neuron not spiking consistently for currents greater than threshold?

Hi I am currently studying physics at the undergraduate level. As part of my final year project Ive got to implement the HH model and investigate certain types of behaviour. My issue is the following. ...
Vishal Jain's user avatar
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How to measure Na/K channel activation at the membrane level?

Assume that there are two different signals occurring on the ECG - during depolarization and repolarization in the standard ECG. I was advised not to use the standard ECG in measuring the exact ...
Léo Léopold Hertz 준영's user avatar
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What is the difference between a graded potential and an action potential?

I was under the impression the only signals neurons send using changes in membrane potential are action potentials. But my biology professor showed us diagrams of graded potentials and action ...
Stan Shunpike's user avatar
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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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Ischemia-induced deploarization in excitable cells

I have read in many sources that ischemia-induced depolarization is due to the opening of ATP-sensitive potassium channels and inactivation of Na/K exchangers [1,2]. However, K-atp channels are inward-...
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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 ...
Stan Shunpike's user avatar
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Sodium-Potassium Pump

From my understanding, in the sodium-potassium pump we have Na+ inside the cell and K+ outside the cell, thus forming a so called "salted banana." After reading my textbook I found many statements ...
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Oscillatory electrical system using a chain of neurons

Many daily activities that we perform are result of inbuilt oscillatory circuits in our body. For example walking, breathing, heart beat, blinking, etc. The coding and decoding of stored memory also ...
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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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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) ...
Black Dagger's user avatar
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Why do the size of the phase 1 notch vary among cardiac cells?

The size of the phase 1 notch varies among cardiac cells. It is prominent in myocytes in the epicardial and midmyocardial regions of the left ventricular wall and in ventricular Purkinje fibers. ...
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electrotonic spread and screening

(In physics.stack I have been suggested to post my question also here.) In the classical theory of passive neurons (where the action potential is not yet excited), the voltage is successfully ...
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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 ...
Alex L's user avatar
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Why do larger neurons have less cytoplasmic resistance?

I'm studying neuron electrochemistry rn and my book basically says that the more the cytoplasm impedes the flow of ions, the slower conduction will be, therefore larger neurons will have lower ...
maximuspinecone's user avatar
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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 ...
user50080's user avatar
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2 answers
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Why is the ordinary cardiac muscle’s target value of the action potential 0mV?

Why do some excitable cells have a target of 0mV for the action potential, even with a slight overshoot? Excitable cells such as muscles and nerves have the ability to rapidly change their membrane ...
Blue Various's user avatar
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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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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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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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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 ...
Ginevra B's user avatar
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Why are nerves blocked even though potassium channels are not blocked?

One could read "Local anesthetics produce a very slight, virtually insignificant, decrease in potassium (K+) conductance through the nerve membrane." At Handbook of Local Anesthesia 7th ...
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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 ...
Ben Hughes's user avatar
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2 answers
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Why does damage to myelin sheath in multiple sclerosis lead to a decrease in information reaching the brain from sensory receptors?

In multiple sclerosis(MS), myelin sheath is attacked and damaged. When this happens, there is a decrease in the amount of information reaching the brain from sensory receptors. How and why does a ...
Donia Elwardany's user avatar
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2 answers
158 views

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 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- "...
Alleged Biologist's user avatar
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1 answer
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Nernst Equation and Membrane Potential

I am a bit confused on how to use the Nernst equation to determine polarization. I saw in the textbook that if potassium channels were open in a neuron cell, there will be a net diffusion of $\ce{K+}$ ...
Jaehyun Ahn's user avatar
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1 answer
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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 ...
stressed out's user avatar
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1 answer
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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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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 "...
Ben Hughes's user avatar
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1 answer
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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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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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Confusion over role of current/potential in Nervous system?

I am taking a course on the nervous system and I am do not have any physics background. Therefore, I would like to know, what are we precisely talking about when we talk about current in the nervous ...
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Chloride Clamp and Nernst potential

The Nernst potential for chloride is -70 mV. The neuronal Resting Membrane Potential (RMP) is -70 mV. Under this condition, if the chloride channels are open (as it happens in Inhibitory Post Synaptic ...
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