OSMT (Ontario Society of Medical Technologists) Practice Exam

When does an action potential occur?

1. A neuron transmits an impulse

2. A neuron is stimulated above the firing level

3. Sodium ions enter the neuron

4. All of the above

The correct answer is: All of the above

An action potential occurs when a neuron becomes sufficiently stimulated to reach a threshold level, leading to a rapid change in membrane potential. This process is initiated when a neuron is stimulated above the firing level. This threshold is critical because if the stimulus is strong enough to surpass this level, it results in depolarization of the neuron's membrane. Once the threshold is reached, sodium ions rapidly enter the neuron through voltage-gated sodium channels. This influx of sodium ions causes a significant deviation in the electrical charge across the membrane, which is the defining feature of an action potential. The simultaneous occurrence of neuronal stimulation, surpassing the firing threshold, and the movement of sodium ions into the neuron are all key components of what happens during an action potential. Therefore, the correct answer encompasses all these aspects, as they collectively describe the conditions and physiological events leading up to and during an action potential. This interconnectedness of neuronal firing and ionic movement illustrates the complexity of the action potential and demonstrates how these elements work together in the functioning of neurons.