13

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 takes to get there. That's okay - it's a mistake that many many people learning about neurophysiology make, including instructors. Na+/K+ concentrations actually ...


9

The key to understanding this is to digest the fact that there are two gates blocking a normal sodium channel. These gates are called the activation gate (on the extracellular side) and the inactivation gate on the intracellular side. Both of these together, or any one of these alone, if closed, can block the sodium current from entering the cell. In the ...


9

Three facts: The K+ ions are heavily concentrated on the inside while the Na+ ions are heavily concentrated on the outside The Na+/K+ ion pump is unidirectional. It can only pump K+ ions inside the cell while expelling the Na+ ions. Finally only the Na+/K+ ion pumps can restore the ionic equilibrium. The full scene: Once the threshold is reached the Na+ ...


7

Remember that the action potential gets more positive in the first place, so increasing positivity is achievable. Net Na+ movement into the cell makes the potential more positive. This occurs as the Na+ gate (right on the image below) are open. The key message is that the membrane can move charge to cause an increase in either positive and negative potential....


6

Short answer An action potential is a binary all-or-nothing event, while a graded potential is an analog signal. Background Action potentials, once initiated, are basically all-or-nothing events. Amplitudes may admittedly be variable, but basically it is the spike rate that is relevant to the neural code (Gerstner et al., 1997). In contrast, graded ...


6

Graded potentials are initiated by a stimulus that vary in magnitude depending on the strength of the stimulus. (The stronger the stimulus the more gated channels open causing larger depolarisation). Graded potentials occur in dendrites, cell bodies and sensory receptors. Graded potentials dissipate with distance from stimulus. On the other hand, action ...


6

Short answer Widening of the action potential increases neurotransmitter release; Generally, an action potential results in the release of about one vesicle of neurotranmitters; An action potential does not have to lead to neurotransmitter release - the chance being anywhere between 9 - 100%, depending on the synapse under investigation. Background ...


6

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 and exchanging it with external potassium at the cost of ATP. However a neuron's rest state (in your example -60 mV) is a combination of the equilibrium of ...


6

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 electromyostimulation, is the elicitation of muscle contraction using electric impulses...The impulses mimic the action potential coming from the central nervous ...


6

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 does not move an equal number of ions in each direction does not actually matter at all for resting membrane potential; the resting membrane potential would be ...


5

Neurons encode the "largness" of the stimulus in firing frequency. Neurotransmitters are stored in vesicules near the end of the axon. It has been shown that neurotransmitter release follows Poisson-distribution and that usually a single "packet" (quantum) is released - this is known as quantal release. Although the actual number of molecules in a single ...


5

The voltage-gated potassium channels are there only to swiftly repolarize the membrane potential. Ultimately it is the Na,K-ATPase that has to pump the various ions back where they belong (Na out, K in), also when potassium channels are active. So when the potassium channels are blocked, the Na,K-ATPase will restore the membrane potential, albeit in the ...


5

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 both ions. If each action potential has (approximately) the same flux of $\ce{Na+}$ and $\ce{K+}$ then higher frequency of action potentials means more flux, ...


4

Nice graph. What happens when you reach the top of the potential (when you depolarize the membrane) that you need to go back to a resting potential to be able to stimulized again. The membrane gets "neutralized" and this reaction often over-shoots and goes below the resting potential, which is quite normal. Before reaching the normal resting potential there ...


4

During the repolarization, relatively few ions need to cross the membrane for the membrane voltage to change and therefore the change in ions concentration outside and inside the cell is neglible. After repolarization, the concentrations are restored by the continuous action of Na⁺/K⁺-ATPase. The same happens for calcium, but I don't know exactly what kind ...


4

Pathological potassium concentration promotes arrhythmia. Increased extracellular potassium inactivates $Na^+$ channels and opens $K^+$ channels, causing the cells to become refractory [1]: Increased extracellular potassium levels result in depolarization of the membrane potentials of cells due to the increase in the equilibrium potential of potassium. ...


4

Your confusion is caused by the assumption that Na+ always leaves the cell and K+ always enters. The Na+/K+ pump is there to maintain membrane potential and relative Na+ and K+ ion concentrations stable inside. When an action potential (AP) is generated, sodium channels open and sodium rushes inside to depolarize the cell( 1st phase of AP). Next, the sodium ...


4

If there is a stimulus at E, there will be depolarization (membrane becomes relatively more positive). It is just that no action potentials are fired. Therefore, if a strong stimulus does arrive, it will depolarize the membrane to an extent depending on its strength. It will increase the height of the succeeding B phase or reduce the dip of the succeeding E ...


4

Short answer Action potentials are mediated by electric currents and can be modeled by electronic circuits. Background An electric current is the flow of charge. Therefore, action potentials are mediated by current flow. However, action potentials are mediated by the flow of ions across the membrane (Fig. 1), whereas current flow in electric circuits is ...


4

First of all, electric current is defined as movement of charges, $I=\frac{dQ}{dt}$. In electronics that you see around that is not very useful definition, because electrons move much slower than signals, that is changing electric field. Speed of electric field propagation reaches speed of light, whereas electrons move at 1%-30% or $c$. In biology, ...


4

Short answer A single pacemaker neuron can generate oscillatory behavior. Background Given our exchange in the comments, I will focus on single neurons with intrinsic oscillatory behavior. For example, thalamocortical relay neurons and inferior olive neurons have intrinsic oscillatory properties, mainly through the interaction of a hyperpolarization-...


4

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 skeletal muscle fibre. Journal of Physiology; 38: 113--133. Adrian, ED (1912). On the conduction of subnormal disturbances in normal nerve. Journal of ...


4

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 with distance d across the membrane and capacitance c. Then we add some myelin to get a new capacitance C at a new distance D. If you 4X the distance between ...


4

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 resting potential in this situation will be something like -70 mV. Rest means that the net current flow is zero; however, there is still current: potassium is ...


4

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 equation, as in the H&H model, are loose. It resemble the equation derived for the movement of a charged particle in a constant field. But it is not an equation ...


3

Current flow is the movement of charged particles (ions in this case). The membrane potential is the charge difference across the cell membrane. Usually there is more negative charge inside the cell than out, so the membrane potential is said to be negative. When ion channels open, typically positive ions (Na+, K+) will flow into the cell as they are flowing ...


3

Did you ever get an answer to your question? I know this may be too late now, but I was noseying around and spotted it, so I'll take a stab nonetheless. I could be wrong, but I suspect what you're seeing here may be an extracellular representation of an action potential (and/or it could be a filtering artefact, see below). From the video on the spikerbox ...


3

When you say multiple simultaneous action potentials I assume that the stimuli for all of them are temporally overlapping. In such case a neuron can integrate the different stimuli and launch an action potential. Of the multiple stimuli some can be excitatory while others can be inhibitory. The net response would be an integration of all the signals [ref]. ...


3

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 explanation seems overly-messed up and confusing) At any moment, the potential difference across the cell membrane has to be such that it makes all fluxes balanced. Let ...


3

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 networks, with regards to Schwann cells, and prevent differences in osmotic pressure from disrupting the cells. As for your second question, action potentials do ...


Only top voted, non community-wiki answers of a minimum length are eligible