Reversal Potential & Acetylcholine Receptor: How Action Potentials Occur at NMJ

[gamecube999]

the reversal potential is about 0mV, so how does opening the acetylcholine receptor at neuromuscular junctions cause action potentials to occur?

 

[quasi426]

Reversal potential is the name give for a specific channel at which point no NET current (ion flux) will occur. Each protein channel will have different reversal potentials based the ions in the environment, the ions "allowed" to pass through the channel, the electrochemical gradients for each of the ions.

The reason an action potential occurs is similar to that of other neurons. There will be a threshold membrane voltage that will lead to opening of sodium channels and this will propagate down the membrane.

 

[ravenprp]

At the neuromuscular junction (NMJ), the reversal potential refers to the membrane potential at which the flow of ions through a specific channel is balanced, resulting in no net movement of ions across the membrane. In the case of acetylcholine receptors (AChR), the reversal potential is approximately 0mV. This means that when the AChR channel opens, ions will flow in both directions equally, resulting in no change in the membrane potential.

So how does the opening of AChR at the NMJ lead to action potentials? This occurs through a process known as depolarization. When the AChR channel opens, positively charged sodium ions (Na+) flow into the muscle cell, causing a slight depolarization of the membrane. This depolarization can reach a threshold level, at which point voltage-gated sodium channels on the muscle cell membrane open, allowing a larger influx of Na+ ions. This influx of Na+ ions leads to a rapid depolarization of the membrane, resulting in an action potential.

In summary, while the reversal potential of AChR at the NMJ is 0mV, the opening of these channels can still lead to action potentials through the process of depolarization. This is a crucial mechanism for the communication between neurons and muscles, allowing for the coordinated contraction of muscles in response to neural stimulation.