13
votes
Accepted
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 ...
- 44k
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 ...
- 52.3k
9
votes
Accepted
At what point during an action potential are the sodium potassium pumps working?
The Sodium-Potassium Pumps are always at work. One can think of them as a continuous process that maintains the equilibrium potential for the individual ions. They always are grabbing internal sodium ...
- 712
8
votes
Accepted
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 ...
- 44k
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 ...
- 14.1k
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 ...
- 44k
6
votes
Accepted
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 ...
- 44k
6
votes
At what point during an action potential are the sodium potassium pumps working?
Very good question. Most of your arguments, to the best of my knowledge are accurate. As to answer your questions, I'll provide a basic model of understanding. (Disclaimer:- I'm sorry if the ...
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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 ...
- 44k
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 ...
- 712
5
votes
Accepted
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 ...
- 44k
5
votes
Accepted
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; ...
- 44k
5
votes
Accepted
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://...
- 44k
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 ...
- 3,065
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 ...
- 44k
4
votes
Accepted
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 ...
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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. ...
- 44k
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 "...
- 354
3
votes
Accepted
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 (...
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3
votes
Accepted
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 ...
- 44k
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 ...
- 4,669
3
votes
Accepted
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 ...
- 44k
3
votes
Accepted
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 ...
- 184
3
votes
Accepted
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 ...
- 44k
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 ...
- 378
3
votes
Accepted
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 ...
- 44k
3
votes
Accepted
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 ...
- 44k
3
votes
Accepted
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 ...
- 44k
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 ...
- 44k
2
votes
Accepted
Dendrodendritic synapse through axodendritic synapse at same dendrite?
I'm not sure if you are asking if an axon that sends a signal to a dendrite would then be released from that dendrite to another dendrite?
I don't see how this is possible seeing as the dendrite is ...
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