What is an action potential?

• A. A change in blood pressure
• B. A rapid rise and fall in membrane potential
• C. An increase in muscle size
• D. A type of neurotransmitter release

Answer: (B)

An action potential is characterized by a rapid rise and fall in membrane potential, which is a critical process in the functioning of neurons and muscle cells. This phenomenon occurs when a neuron depolarizes, leading to a significant change in the electrical charge across the membrane. Initially, the membrane potential becomes more positive due to the influx of sodium ions, followed by a rapid repolarization where potassium ions exit the cell, restoring the negative charge. This sequence of depolarization and repolarization is what defines an action potential.

This mechanism is essential for the transmission of signals along neurons, allowing for communication between cells and the propagation of nerve impulses. The precise and rapid shifts in membrane potential are vital for the proper function of both the nervous system and the muscular system, enabling responses to stimuli and facilitating coordinated movements.

While changes in blood pressure, increases in muscle size, and neurotransmitter release are important physiological processes, they do not describe the electrical events that occur during an action potential. Understanding the nature of action potentials provides insight into how electrical signals are generated and transmitted in the body, which is foundational knowledge in physiology.