What is primarily affected when a neuron fires an action potential?

When a neuron fires an action potential, the primary change that occurs is in the electrical charge inside the neuron. This process starts when the neuron reaches a certain threshold of depolarization, which is primarily due to the influx of sodium ions through sodium channels. As these channels open, the inside of the neuron becomes more positively charged compared to the outside, creating a rapid change in membrane potential that constitutes the action potential.

Following the depolarization phase, the neuron then enters repolarization, where potassium channels open, allowing potassium ions to exit the cell. This sequence of events is crucial for the propagation of the action potential along the axon and ultimately leads to neurotransmitter release at the synapse.

While the strength of the impulse, the production of neurotransmitters, and blood flow to the brain are important aspects of neuronal function, they are not directly altered during the firing of an action potential. The defining feature of an action potential is its reliance on the rapid changes in the electrical charge within the neuron itself.