Action potentials (nerve impulses) are changes in the membrane potential that, once started, will affect the entire excitable membrane. the first action potential is usually generated at the initial segment of the neuron’s axon. this activity will test your understanding of the sequence of events that occur at the membrane of the initial segment of the axon during generation of an action potential.

The neurons interact with each other at synapse through action potential generated in response to the stimulus. At the resting phase, all the ion channels remain closed and the cell maintains a high amount of Na⁺ ions outside the cell and a high amount of K⁺ ions inside the cell. This difference maintains the membrane potential at -70mv.

When a stimulus activates a cell receptor, it causes the opening of the sodium channels in response to either mechanical stimulus or neurotransmitter released due to stimulus. The opening of the sodium channels leads to the influx of  Na⁺ ions which changes the potential from -70 mv to more positive value. When this change in membrane potential reaches - 55 mv it leads to the opening of the voltage-gated channels which causes an influx of Na⁺ ions. This more influx of  Na⁺ ions leads to depolarization when the membrane reaches above the threshold and the action potential is generated in the neuron.

i believe it would be the lungs.