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.

Filter by
Sorted by
Tagged with
4 votes
1 answer
66 views

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-...
3 votes
1 answer
74 views

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 ...
0 votes
0 answers
39 views

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 ...
  • 313
2 votes
2 answers
62 views

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 ...
1 vote
0 answers
16 views

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 ...
2 votes
0 answers
91 views

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 ...
  • 89
1 vote
1 answer
318 views

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 ...
  • 89
2 votes
2 answers
728 views

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 ...
  • 231
1 vote
0 answers
24 views

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 ...
  • 111
1 vote
1 answer
115 views

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 ...
  • 19
1 vote
0 answers
46 views

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 ...
5 votes
1 answer
132 views

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. ...
1 vote
1 answer
35 views

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 ...
1 vote
1 answer
73 views

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 ...
  • 113
0 votes
0 answers
72 views

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!
  • 275
0 votes
1 answer
36 views

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 ...
  • 139
0 votes
1 answer
44 views

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 ...
  • 137
0 votes
0 answers
23 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 ...
  • 1
1 vote
1 answer
90 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 ...
2 votes
1 answer
165 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 ...
2 votes
2 answers
124 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 ...
  • 137
6 votes
1 answer
681 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 ...
0 votes
0 answers
58 views

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 ...
  • 319
0 votes
0 answers
26 views

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 ...
1 vote
1 answer
49 views

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, ...
2 votes
1 answer
122 views

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 ...
  • 21
3 votes
0 answers
94 views

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 ...
  • 31
1 vote
0 answers
34 views

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 ...
  • 131
1 vote
1 answer
112 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 ...
  • 320
1 vote
1 answer
778 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 ...
  • 105
2 votes
1 answer
1k 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 ...
3 votes
1 answer
54 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 ...
2 votes
1 answer
239 views

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 ...
  • 228
1 vote
1 answer
152 views

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 ...
  • 228
1 vote
0 answers
112 views

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 ...
3 votes
2 answers
761 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 ...
0 votes
0 answers
28 views

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 ...
  • 228
1 vote
0 answers
47 views

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 ...
6 votes
1 answer
131 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 ...
1 vote
1 answer
73 views

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, ...
2 votes
1 answer
82 views

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 "...
0 votes
1 answer
176 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 ...
1 vote
1 answer
60 views

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? ...
3 votes
1 answer
109 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 ...
1 vote
0 answers
103 views

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 ...
  • 111
2 votes
2 answers
919 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 ...
  • 43
2 votes
2 answers
340 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 ...
1 vote
2 answers
2k 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-...
  • 255
2 votes
2 answers
60 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 ...
0 votes
1 answer
631 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 ...