What is an action potential?

From the Guidelines

An action potential is a rapid electrical signal that occurs when a cell is stimulated beyond its threshold, causing a sudden, temporary reversal of electrical charge across the cell membrane, as described in the context of cardiac cells by the 2017 AHA/ACC/HRS guideline 1.

Key Characteristics of Action Potentials

• They are rapid electrical signals that travel along the membrane of a cell.
• They occur when a cell is stimulated beyond its threshold, causing a sudden, temporary reversal of electrical charge across the cell membrane.
• This process begins with depolarization, which can be influenced by various factors including ion channels and currents, as discussed in the 2017 AHA/ACC/HRS guideline 1.
• The entire cycle typically lasts only a few milliseconds and propagates in a wave-like manner.

Mechanisms and Triggers

• In cardiac cells, action potentials can be triggered by early afterdepolarizations or delayed afterdepolarizations, as explained in the 2017 AHA/ACC/HRS guideline 1.
• Early afterdepolarizations occur during late phase 2 or early phase 3 of the action potential, while delayed afterdepolarizations occur after complete membrane repolarization.
• These mechanisms can lead to various arrhythmias, including torsades de pointes VT and polymorphic VT/VF, highlighting the importance of understanding action potentials in cardiac function and dysfunction.

Comparison with Other Evidence

• Although the 2002 ATS/ERS statement on respiratory muscle testing 1 discusses action potentials in the context of muscle fibers, the fundamental principles of action potentials as rapid electrical signals remain consistent across different cell types.
• The 2017 AHA/ACC/HRS guideline 1 provides more recent and specific information on action potentials in cardiac cells, making it the preferred source for understanding action potentials in this context.
• Therefore, based on the most recent and highest quality evidence, action potentials should be understood as critical events in cardiac cell function, with a clear grasp of their mechanisms and triggers being essential for managing and preventing cardiac arrhythmias 1.

From the Research

Definition of Action Potential

• The action potential is a non-linear, self-propagating, regenerative wave of electrical activity that travels along the surface of nerve cells 2.
• It is a regenerative electrical phenomenon observed on excitable cell membranes that allows the propagation of signals without attenuation 3.
• The action potential is a rapid rise and fall of the electrical membrane potential, resulting from the depolarization-induced, voltage- and time-dependent opening and closure of ion channels in the membrane 2, 4.

Characteristics of Action Potential

• The action potential is characterized by a sudden and transient alteration of the transmembrane potential, caused by changes in ionic conductance across the membrane 2.
• It is carried forward and spreads over long distances by means of both active and passive conduction, dependent on local current flow by diffusion of Na+ ions in the neuronal cytoplasm 2.
• The action potential has a refractory period, which is a critical component of its computational capabilities 5.

Mechanisms Underlying Action Potential

• The action potential is generated by the collective material properties of the lipid bilayer neuronal membrane and the cytoskeletal protein polymers 2.
• The electrical characteristics of the action potential are presented as the result of the depolarization-induced, voltage- and time-dependent opening and closure of ion channels in the membrane, allowing the passive flow of charge, particularly in the form of Na+ and K+ ions 2.
• The action potential pulse (APPulse) is made up of the action potential combined with a coupled synchronized soliton pressure pulse in the cell membrane 5.

Role of Action Potential in Neuronal Function

• The action potential is the cornerstone of neurophysiology, allowing the propagation of signals without attenuation 3.
• It plays a critical role in neuronal excitability, signal transport, and communication within the brain 2, 5.
• The action potential is also involved in various other cellular processes, including cell cycle, cell-volume control, proliferation, muscle contraction, and wound healing 6.