Questions tagged [electrophysiology]

The study of the electrical properties of biological cells and tissues.

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Mapping Ion Channel mRNA Copy Number to Channel Conductance

At least in invertebrates, it appears that within identified cell types, there are robust correlations between ion channel mRNA copy number (as identified by single-cell qRT-PCR) and the maximal whole-...
nguzman's user avatar
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Why don't membrane potentials violate the principle of electroneutrality?

The principle of electroneutrality states that the number of anions and cations in a solution must be the same, i.e., that there will be no charge excess in any side of the membrane separating two ...
TheAnonymous's user avatar
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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
2 votes
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Why do V_Na and V_K stay unchanged in Hodgkin-Huxley model?

In the Hodgkin-Huxley model, ionic current $i_\mathrm{Na}$ and $i_\mathrm{K}$ are given by $$ i_\mathrm{Na}=g_\mathrm{Na}(V_\mathrm{m}-V_\mathrm{Na})\\ i_\mathrm{K}=g_\mathrm{K}(V_\mathrm{m}-V_\mathrm{...
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Why is there a negative sign before voltage in the gate variable functions of the Hodgkin-Huxley model?

In Hodgkin and Huxley's articles (1952, J. Physiol.; 1990, Bulletin of Mathematical Biology), the gate variables are formulated as In particular, as $V$ increases, $\alpha_n$ decreases and $\beta_n$ ...
Jasmine'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 ...
cash999's user avatar
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Electrodes for electroporation of bacterial cells

Wikipedia says "The process {electroporation} requires direct contact between the electrodes and the suspension." However I've read the process is an effect of the field strength alone, ...
Oliver Walters's user avatar
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Confusion regarding the role of the capacitor in the electrical equivalent of a membrane

I am having trouble understanding the electrical equivalent of a cell mebrane as it is shown in this picture taken from Kandel: What I cannot understand is the capacitor in the specific image. Why is ...
Kani Pen's user avatar
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Heart rate sensor electrodes to be used for blink detection (simple EOG)

I have a cheap ECG/HRV/heart rate sensor module for Arduino, bought from Aliexpress. It has 3 electrodes: RA, LA, RL, which I guess mean right arm, left arm, right leg. The module outputs one single ...
LimeAndConconut's user avatar
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Can a dead fish be made to twitch via electrostimulation?

Galvani in the 1700s famously showed that a dead frog can be made to twitch by electric stimulation. The hind legs are particularly susceptible. Salt helps in the activation, as shown in these videos: ...
have_beard_will_ski's user avatar
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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-...
kljiuklk 1's user avatar
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conduction in unmyelinated axons

(Not a specialist here) Several questions touch the voltage propagation along an unmyelinated axon, but I'd like to focus on the following. How fast does the voltage of a sub-threshold perturbation ...
scrx2's user avatar
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What's the effect of prolonged threshold stimulus currents on action potentials?

I've been confused as to what exactly occurs when a current is injected into a membrane, throughout the duration of an action potential. My main source of confusion has been trying to reconcile 2 ...
AllelesWearHeels's user avatar
3 votes
1 answer
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Stimulus currents and neuronal responses

As I understand it, if a subthreshold current of unlimited duration is injected in a neuron, a passive response is observed, like an RC circuit. The membrane potential is depolarized by some arbitrary ...
AllelesWearHeels's user avatar
3 votes
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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
25 votes
2 answers
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Why do blood vessels in the eye not obstruct vision?

As light enters the eye, it reaches the photoreceptors at the "base" of the retina, which then pass that signal to the bipolar and ganglionic neurons -- the latter of which send the signal ...
theforestecologist'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 ...
Quique's user avatar
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How Fast can the Electrochemical Gradient on a Neuron be Reestablished? [duplicate]

The electrochemical gradient of Na+, K+, Ca2+, and Cl- between the inside and outside of a neuron is vital for its function. When a neuron fires, this gradient reverses. How long does it take for the ...
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GHK Equation and Action potential

Can GHK equation be used to predict the membrane potential even if the cell is not at resting state? To say it again, can we use GHK equation at every moment during Action potential? I'm confused ...
한민우's user avatar
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Using Nerve Conduction Studies to determine nerve regeneration

I was reading a paper investigating using MRI as a way to determine peripheral nerve regeneration: https://sci-hub.do/10.1016/j.expneurol.2009.10.012 They mention that ... nerve conduction studies ...
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Potential obstacles to growing nanoelectronics within living cells? [closed]

Say there was a nanotechnology allowing to "grow" and wire up electronic components/sensors measured only a few nanometers in cross-section, though spanning in length across microns. Say ...
Greendrake's user avatar
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Can high energy photoelectrons damage cell membranes?

I've read that in addition to ionizing radiation causing damage to DNA through direct absorption, but DNA can also be damaged through photoelectrons with enough energy. The thing I was wondering is ...
Tom's user avatar
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How many Watt-hours can an electric eel produce in a day?

Electric eels are cited as being about to produce about 860 watts of energy. But I haven't been able to find information on how long they can sustain their charge. https://www.youtube.com/watch?v=...
Johnny's user avatar
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Do electric eels produce current as they just move about, and how/why?

https://www.youtube.com/watch?v=y9wktSQdyaE This video demonstrates how an electric eel can supposedly produce up to 800 watts, and power a Christmas tree, which is very topical (a late Merry ...
Johnny's user avatar
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How can I simulate heart electrical activity in a 2D plane?

I am not a biologist/medical student, I study software engineering. But I really like when medicine and engineering hold their hands together to achieve great things. As a side/toy project, I was ...
Pedro D.'s user avatar
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1 answer
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What is a "membrane holding potential"?

What is a membrane holding potential? I have come across this term but haven't been able to find a definition. From "Voltage-gated sodium channels as therapeutic targets in epilepsy and other ...
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Is there a way to derive Bazett's formula to correct QT interval in ECG?

As we know that QT interval in ECG is a function of heart rate (HR) and to comment on the pathology associated with altered QT interval, we must neutralise the effect of HR. For this Bazett's formula ...
ANA negative's user avatar
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31 views

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 ...
Brian's user avatar
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-1 votes
1 answer
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What's a cells membrane potential without any leak channels?

Consider the following ion concentrations on either side of a cell membrane (in = inside cell, out = outside cell): $[\text{Na}^+]_{\text{in}} = 10mM$, $[\text{Na}^+]_{\text{out}} = 142mM$, $[\text{K}^...
Jane's user avatar
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Why is the current flow shown to be flowing from the negative area towards the positive area?

When I was studying the ECG chapter in the book "Guyton and Hall Textbook of Medical Physiology", I noticed something odd in one of the pictures: As you can see the current is shown to be ...
IdaM's user avatar
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2 votes
1 answer
362 views

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 ...
pincushion44's user avatar
1 vote
2 answers
656 views

At small axon diameters (<1 µm), why does myelination not increase neuronal conduction velocity?

As per the diagram below (and other graphs available online), why do unmyelinated fibres have a higher conduction velocity than myelinated fibres when the axon diameter is less than around 1 µm?
pincushion44's user avatar
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Effect of opposing electric charges on cells

Is the affect on a cell between two negatively charged plates theoretically similar to between a positively and negatively charged plate? In other words, would it induce charges on the inside and ...
Tom's user avatar
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Is there a proton gradient across the cell membrane, just like for the mitochondrial membrane?

Mitochondria have a proton gradient, is there also a proton gradient between cells and the extracellular medium?
Mitchell's user avatar
3 votes
1 answer
874 views

What is the significance of the amplitude of brain waves?

What does the amplitude of brain waves represent and to what neuronal activities is this amplitude related to? For example, in a hypothetical situation, the frequency of brain waves is kept the same, ...
Rohin's user avatar
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1 answer
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Question about the Derivation of the cable equation for neurites

I read in Wikipedia how the cable equation was derived (here) and had a specific problem regarding one of its equation: At the start of the derivation it states that we first need to pretend that the ...
Idop11's user avatar
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1 answer
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Why the length constant of passive current flow isn't depend on the membrane capacitance?

I read that the equation for the length constant for passive conductance along a neuron depend on the resistance of the plasma membrane, the intracellular axoplasm and the extracellular medium. My ...
Idop11's user avatar
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2 votes
1 answer
490 views

Help me understand voltage patch clamping

Before I type my question it is important to know that I already tried looking this up on my own and could not find an answer because the answers are all in complicated physics terms and this topic is ...
Alara's user avatar
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4 votes
1 answer
341 views

electrostatic charge of viruses, especially Coronaviruses

I am searching for (and failing to find) literature about the electric charge (+/-) of viruses, specifically the Coronaviruses. I am aware that it is a complicated issue, including interaction of pH ...
ChrisM's user avatar
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1 answer
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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, ...
Charles C.'s user avatar
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0 answers
32 views

Does the zeta potential of a nanoparticle generally take into account ligand charge?

For example, if I had a quantum dot nanoparticle with conjugated linker peptides capped with polyarginine tracts. Would the localization of negative charge from arginine change the zeta potential ...
Mchiribo's user avatar
1 vote
1 answer
174 views

In the PR segment of an ECG, how come there's no current flowing?

I don't really know how to phrase the question, but to put it as clearly as I can, I don't get why it is the P wave "flattens down" when the atria have completely depolarized. I get that the ...
Dahen's user avatar
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1 vote
1 answer
179 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 ...
mohamed's user avatar
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1 answer
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Difference between Premature Atrial Contraction and Atrial Fibrillation

what is the difference between Premature Atrial Contraction and Atrial Fibrillation. I know that both have irregular heart beat but have normal QRS complex. Both have abnormal or absence P waves but a ...
Larry To's user avatar
2 votes
1 answer
42 views

Definition for different arrhythmia

I am wondering if there is an organization, a document or a research that standardize all the rhythms? Such as describing how long should the ECG be flatline to be considered as asystole? The rhythm I ...
Larry To's user avatar
6 votes
1 answer
146 views

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
1 vote
0 answers
32 views

Is the medium which transmits the electrical impulse through the heart different to a nerve?

According to Nerve A nerve is an enclosed, cable-like bundle of nerve fibres called axons Being an Axon An axon (from Greek ἄξων áxōn, axis), or nerve fiber, is a long, slender projection of a ...
Pablo's user avatar
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6 votes
1 answer
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Why do larger diameter myelinated axons have greater conduction velocities than small diameter myelinated axons?

A canonical statement I have frequently read is that "large diameter axons conduct action potentials at faster velocities than small diameter axons". After recently learning the effect of increased ...
S.C.'s user avatar
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1 vote
0 answers
157 views

Are large cell bodies of neurons harder to depolarize than small cell bodies of neurons?

In order for the axon to initiate an action potential, we know that the axon initial segment must be brought to threshold. So my question is as follows: Say we have the minimum charge input, "X", ...
S.C.'s user avatar
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0 answers
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What is the difference in the electrical excitability between a "large diameter soma" and a "large diameter axon"

There are two stereotyped statements that I have seen during my coursework regarding electric properties of neurons: Large diameter axons propagate action potentials more quickly than small diameter ...
S.C.'s user avatar
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