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13 votes
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Purpose of K+ channels in action potential

Great question! However, your question is based on some misconceptions about what polarization means and how ion movement is involved, as well as the difference between equilibrium and the time it ...
Bryan Krause's user avatar
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11 votes

Why are nerves blocked even though potassium channels are not blocked?

In general, action potentials are initiated by an inflow of Na+ that depolarizes the neuron. Only after that, K+ channels open up that re-polarize the membrane potential to get the neuron back in ...
AliceD's user avatar
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8 votes
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Why does resting potential not become continually more negative?

The resting membrane potential is due to internal/external differences in ion concentrations and very importantly differences in permeability to those ions. The fact that the sodium/potassium pump ...
Bryan Krause's user avatar
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7 votes

Why does an electric shock contract the muscle?

Nice Question! Lets first introduce ourselves to the topic i.e. Electrical Muscle Stimulation. Electrical muscle stimulation (EMS), also known as neuromuscular electrical stimulation (NMES) or ...
another 'Homo sapien''s user avatar
7 votes
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Why does hypercalcemia cause muscle weakness, yet hyperkalemia causes muscle excitation?

You're correct about your reasoning for potassium; high extracellular potassium concentration reduces the concentration gradient of potassium across the membrane, pushing the reversal potential for ...
Bryan Krause's user avatar
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6 votes
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What is the mechanism by which myelination reduces the capacitance of the axon membrane?

Circuit analogies don't 100% apply to myelin because membranes have complex electrical properties, but both of those explanations work and they are in fact essentially interchangeable: Take a membrane ...
Bryan Krause's user avatar
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6 votes
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Why do ion leak channels exist?

Check the parameters that go into the Goldman equation... it shows that permeability of ions is as important as their concentrations. If the permeability is zero, there is no potential. Because other ...
Bryan Krause's user avatar
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5 votes
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Why nerve fibre is infatiguable?( is my conjecture correct?)

One can imagine that each action potential causes a small amount of $\ce{Na+}$ goes inside the cell, and a small amount $\ce{K+}$ goes outside the cell, thus weakening the electrochemical gradient of ...
xelo747's user avatar
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5 votes
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Hodgkin huxley neuron not spiking consistently for currents greater than threshold?

This is happening due to sodium channel inactivation. Some relevant sources: https://en.wikipedia.org/wiki/Ball_and_chain_inactivation https://www.st-andrews.ac.uk/~wjh/hh_model_intro/ (I guess this ...
Bryan Krause's user avatar
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5 votes
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Understanding the voltage of a living cell

Voltage is always a potential difference, so you need two "points" to define one. Technically speaking, a neuron doesn't have a voltage and the extracellular space doesn't have a voltage; ...
Bryan Krause's user avatar
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5 votes
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Ischemia-induced deploarization in excitable cells

Inward-rectifying means positive current passes more easily in the inward direction, however it won't flow differently than the membrane voltage and reversal potential dictate. See for example https://...
Bryan Krause's user avatar
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4 votes
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Original paper about the all or none law for neurons

This probably goes back to Lucas (1909), Adrian (1912), and Bernstein (1912). But the idea might have started from Helmholtz (1850). Lucas, K (1909). The ``all or none'' contraction of the amphibian ...
Memming's user avatar
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4 votes
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Neuronal membrane resting potential for large cells

In a typical neuron at rest, potassium is high inside the cell and low outside, with the opposite true for sodium. The membrane is mostly permeable to potassium. Let's ignore the other ions. The ...
Bryan Krause's user avatar
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4 votes
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Where does this equation in the electrophysiology literature form come from?

They chose that equation mainly because of numerical simplicity. It can fit the rates $\alpha$ and $\beta$ for all the ion channel particles in the model. The theoretical foundation for the ...
heracho's user avatar
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4 votes

Why does damage to myelin sheath in multiple sclerosis lead to a decrease in information reaching the brain from sensory receptors?

As you write in your question, myelin is an insulating sheath that speeds neuronal transmission. However, the mechanism for transmission in myelinated axons is very different from unmyelinated fibers. ...
Bryan Krause's user avatar
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4 votes

Why do larger neurons have less cytoplasmic resistance?

Neurons are like leaky cables. If you make them longer, the resistance increase (along the long axis); if you make them thicker (larger cross-sectional area), the resistance decrease. The word "...
X Zhang's user avatar
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3 votes
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How greater magnitude implies greater frequency of action potential?

There are several important points to answering your question, each somewhat independent of the others. First, lets think about this problem from the perspective of the axon hillock, where action ...
Bryan Krause's user avatar
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3 votes
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What are negative and positive after potentials?

Yes, you are correct. The negative current is hyperpolarising the axon and the positive current is returning it to baseline from a hyperpolarised state. They are often referred to as inward/outward (...
Oliver Houston's user avatar
3 votes
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Why summation takes place at Initial segment?

Why don't EPSPs travel passively through axons? EPSPs decay over distance. The decay is described by the length constant, which can be calculated based on the electrical properties of some ...
Bryan Krause's user avatar
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3 votes

How does entry of Ca²⁺ to the myocardiocyte make it more contractible?

The answer is a bit more complex. Calcium ions have a lot of effects in the cardiac myocyte. Apart from the increased contractility (positive inotropy), extracellular calcium concentration also alters ...
stochastic13's user avatar
  • 4,689
3 votes
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Do Schwann cells have Na+/K+ ATPase pump?

Yes. Although utilizing the action potential is not in their function, Schwann cells do have Na/K ATPases. In fact all animal cells do. It contributes to the resting membrane potential in neural ...
Liu Tianyi's user avatar
3 votes
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How does (action potential) hyper-polarisation work?

I'll borrow a diagram from another answer to a similar question, but not quite a duplicate (I hope @AliceD won't mind my laziness): Fig. 1. Refractoriness. source: University of British Columbia One ...
Bryan Krause's user avatar
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3 votes

What material fills the synaptic cleft? Is it water?

There are two types of synapses namely Electrical synapse and Chemical synapse. In electrical synapse there is physical contact between two cells through gap junctions. In chemical synapse there is a ...
Science123's user avatar
3 votes
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Relationship between membrane current and voltage in neurons

This is a bit of a strange way to plot out these data, I think Figure 3.2 is easier to understand, but basically these are data plotted from early voltage-clamp experiments trying to walk you through ...
Bryan Krause's user avatar
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3 votes
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What causes sodium channels to open?

Sodium channels are primarily voltage-gated - these are the channels responsible for action potentials. Many other receptors are ligand-gated, and these are typically the signal that causes the ...
Bryan Krause's user avatar
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3 votes
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How are Current Sources and Sinks for Postsynaptic Potentials defined?

Sinks and sources just refer to the sign of the local field potential measured with extracellular electrodes. Excitation involves positive charges entering cells, depolarizing them. When positive ...
Bryan Krause's user avatar
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3 votes

electrotonic spread and screening

In biological membranes, the primary physics principle resisting change in voltage is described by capacitance of the membrane, which is a key aspect of the cable equations. If you model some ...
Bryan Krause's user avatar
  • 45.9k
3 votes

Nernst Equation and Membrane Potential

Are you just counting up the potassium ions and subtracting them? Don't do that! That's not how it works. Potassium ions don't just exist by themselves, they come paired with negative ions of some ...
Bryan Krause's user avatar
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3 votes

Membrane Potential Question

Usually we use the Goldman Equation when calculating membrane potential with multiple ions and the Nernst equation for calculating reversal potentials for individual ions. Try out the Goldman Equation ...
Bryan Krause's user avatar
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2 votes

How does a higher channel density increase speed of propagation of an Action Potential?

As @another'Homosapien' mentioned in the comments, the reality is actually the opposite: action potential speed is inversely proportional to channel density. In other words: lower channel density ...
theforestecologist's user avatar

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