What effect do positive ions have on neuronal firing?

Positive ions, particularly sodium (Na+) and calcium (Ca2+), play a crucial role in the process of neuronal firing, specifically in the generation and propagation of action potentials. When a neuron receives a signal, certain channels in its membrane open, allowing these positive ions to flow into the cell.

This influx of positive ions depolarizes the neuron's membrane, making the inside more positively charged compared to the outside. If the depolarization reaches a certain threshold, it triggers the opening of more voltage-gated channels and leads to a rapid rise in membrane potential — this is the action potential. The action potential is essential for the transmission of signals along the neuron and to other neurons, enabling communication within the nervous system.

In contrast, the other options lack the essential mechanisms involved in neuronal firing. For example, inhibition of firing or a decrease in stability would prevent the neuron from reaching the action potential threshold, while no effect on firing does not account for the fundamental role that positive ions play in excitability and signal transmission in neurons. Thus, the correct understanding reflects that positive ions directly facilitate and allow neuronal firing, making the correct answer evident.