"An action potential occurs when the membrane potential of a specific cell rapidly rises and falls."
A brief electrical signal that travels down the axon of a neuron. These are the means by which neurons communicate with each other.
Resting membrane potential: The electrical potential difference across a neuron's membrane when it is at rest.
Excitatory and inhibitory postsynaptic potentials: Changes in the membrane potential caused by the binding of neurotransmitters to postsynaptic receptors.
Threshold potential: The critical membrane potential at which an action potential is triggered.
Depolarization: The process by which the membrane potential becomes less negative, usually due to the influx of positively charged ions.
Repolarization: The process by which the membrane potential returns to its resting level, typically due to the efflux of positively charged ions.
Hyperpolarization: An excess polarization of the neuron's membrane potential, usually caused by the efflux of negatively charged ions.
Refractory period: The period immediately following an action potential during which the neuron is temporarily unresponsive to further depolarization.
Voltage-gated ion channels: Specialized membrane proteins that control the passage of ions across the membrane and play a critical role in action potential generation.
Saltatory conduction: The process by which action potentials jump between nodes of Ranvier, allowing for faster transmission of signals along myelinated axons.
Action potential propagation: The movement of an action potential along an axon or dendrite.
Resting potential: This is the baseline transmembrane potential of a neuron when it is inactive. In this state, the inside of the cell is negatively charged compared to the outside, and the ion channels are closed.
Threshold potential: This is the level of depolarization required to trigger an action potential. When the threshold potential is reached, ion channels open and there is a rapid influx of sodium ions into the cell, causing depolarization.
Rising phase: In this phase, the depolarization of the neuron reaches a peak as the sodium ions continue to rush into the cell, and the cell membrane potential rapidly increases. This stage is also called depolarization.
Falling phase: In this phase, the membrane potential rapidly returns to its resting level due to the rapid efflux of potassium ions from the cell. This portion is also called repolarization. The membrane potential can sometimes overshoot the resting level, creating a hyperpolarization phase.
"Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and in some plant cells."
"In neurons, action potentials play a central role in cell-cell communication by providing for the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon."
"In muscle cells, for example, an action potential is the first step in the chain of events leading to contraction."
"In beta cells of the pancreas, they provoke release of insulin."
"Action potentials in neurons are also known as 'nerve impulses' or 'spikes'."
"Action potentials are generated by special types of voltage-gated ion channels embedded in a cell's plasma membrane."
"These channels are shut when the membrane potential is near the resting potential of the cell, but they rapidly begin to open if the membrane potential increases to a precisely defined threshold voltage."
"When the channels open, they allow an inward flow of sodium ions, which changes the electrochemical gradient, producing a further rise in the membrane potential towards zero."
"This then causes more channels to open, producing a greater electric current across the cell membrane and so on."
"The rapid influx of sodium ions causes the polarity of the plasma membrane to reverse."
"Potassium channels are then activated, and there is an outward current of potassium ions, returning the electrochemical gradient to the resting state."
"After an action potential has occurred, there is a transient negative shift, called the afterhyperpolarization."
"Sodium-based action potentials usually last for under one millisecond."
"Calcium-based action potentials may last for 100 milliseconds or longer."
"In some types of neurons, slow calcium spikes provide the driving force for a long burst of rapidly emitted sodium spikes."
"In cardiac muscle cells, on the other hand, an initial fast sodium spike provides a 'primer' to provoke the rapid onset of a calcium spike, which then produces muscle contraction."
"The specific types of cells mentioned that can generate action potentials are neurons, muscle cells, some plant cells, pancreatic beta cells, and certain cells of the anterior pituitary gland."
"Action potentials play a central role in providing for the propagation of signals along the neuron's axon toward synaptic boutons situated at the ends of an axon."
"A neuron that emits an action potential, or nerve impulse, is often said to 'fire'."