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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To where exactly does the sarcoplasmic reticulum release its calcium when stimulated?

I`m reading through medical physiology (2nd ed) by Boron & Boulpaep. On page 240 when describing the mechanism behind muscle activation, they write the following: After depolarization of the L-...
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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 ...
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When an action potential reaches an axon terminal

I came across the following question in my study of action potentials in neurons: When an action potential reaches an axon terminal: A. Na+ channels close. B. K+ channels open. C. The interior of the ...
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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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Action Potential and Impulse Direction

My textbook describes generation of action potential due to an "induced increased membrane permeability to $Na$+ ions" and presents the ad hoc fact that electric current would flow from the ...
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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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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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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 ...
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How much charge is moved for one heart beat?

Roughly, how much charge cycles (in and out of our heart cells) for each heart beat? I am just looking for the total number of Coulombs, but, since all charge can apparently be accounted for with just ...
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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 ...
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Impact of increased sodium conductance at a neuromuscular junction

If trans-epithelial Na+ transport were to increase at the synapse(please consider both pre and post-synaptic membrane situations) in a neuromuscular junction, how would that manifest itself? My guess ...
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What exactly are the gates in Hodgkin Huxley model?

Hodgkin & Huxley found that a model with 4 gates in series produces a good fit to the S-shaped curve of the potassium current during the action potential. Upon reading about the structure of ...
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Understanding the voltage of a living cell

Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work ...
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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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Effects of high extracellular fluid calcium ion concentration - what's the reason behind it?

The Guyton and Hall Textbook of Medical Physiology, p. 76, says: For example, a high extracellular fluid calcium ion concentration decreases membrane permeability to sodium ions and simultaneously ...
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What would happen to the membrane potential if a cell didn't have developed relative refractory period?

If the Na+ voltage gated channels remain open instead of getting deactivated during the re-polarization period, would the membrane potential become 0 since the Na+ ions would be constantly bringing ...
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Illustrating Action Potential Conduction and Ion-Gated Channels

I can separately illustrate action potential and ion-gated channels along an axon. However, I am not sure if I did the right thing on the picture below. What I'm trying to show are the simultaneous ...
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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. ...
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How does slowed action potential propagation in the optic nerve cause blurred vision?

Multiple sclerosis is accompanied by optic neuritis, and there is demyelination of the optic nerve, causing the action potential to be propagated more slowly along axons. But how does this lead to ...
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How are Current Sources and Sinks for Postsynaptic Potentials defined?

I am currently reading "Electric Fields of the Brain" by Paul Nunez, and encountered this passage: The synaptic inputs to a neuron are of two types: those that produce excitatory ...
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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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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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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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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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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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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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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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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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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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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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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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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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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 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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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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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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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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