Action potential: Difference between revisions

Latest revision as of 20:11, 18 February 2025

An action potential is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane with a characteristic pattern. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells, as well as in some plant cells.

Overview[edit]

An action potential is a fundamental feature of the nervous system and is essential for the propagation of signals along the axon of a neuron. It is a transient event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory.

Phases of an Action Potential[edit]

Resting Potential[edit]

The resting potential is the baseline state of the neuron, typically around -70 mV. This is maintained by the sodium-potassium pump and the differential permeability of the membrane to sodium and potassium ions.

Depolarization[edit]

During depolarization, voltage-gated sodium channels open, allowing sodium ions to flow into the cell. This causes the membrane potential to become more positive.

Repolarization[edit]

Repolarization occurs when the sodium channels close and voltage-gated potassium channels open, allowing potassium ions to flow out of the cell, returning the membrane potential to a negative value.

Hyperpolarization[edit]

Hyperpolarization is a phase where the membrane potential becomes more negative than the resting potential. This is due to the continued efflux of potassium ions.

Refractory Period[edit]

The refractory period is a period of time during which a neuron is unable to fire another action potential. It consists of the absolute refractory period and the relative refractory period.

Propagation of Action Potentials[edit]

Action potentials propagate along the axon of a neuron. In myelinated axons, the action potential jumps between nodes of Ranvier in a process called saltatory conduction. This increases the speed of transmission.

Role in Synaptic Transmission[edit]

Action potentials play a crucial role in synaptic transmission. When an action potential reaches the axon terminal, it triggers the release of neurotransmitters into the synaptic cleft, which then bind to receptors on the postsynaptic neuron.

Pacemaker Potentials[edit]

Pacemaker potentials are spontaneous depolarizations that occur in certain types of cells, such as those in the sinoatrial node of the heart. These potentials are responsible for initiating the rhythmic contractions of the heart.

Related pages[edit]

Gallery[edit]

Animation of an action potential.
Basic shape of an action potential.
Graph of an action potential.
Illustration of action potential in a nerve.
Membrane permeability during an action potential.
Diagram of a synapse.
Graph of a pacemaker potential.
Image of a neuron.
Conduction velocity and myelination.
Cable theory in neurons.
Gap junctions in cells.

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-{{Short description|A brief overview of action potentials in neuroscience}}
+An '''action potential''' is a rapid rise and subsequent fall in voltage or membrane potential across a cellular membrane with a characteristic pattern. Action potentials occur in several types of animal cells, called [[excitable cells]], which include [[neurons]], [[muscle cells]], and [[endocrine cells]], as well as in some plant cells.
-==Action Potential==
+==Overview==
-An '''action potential''' is a rapid, temporary change in a cell's membrane potential, which is a fundamental mechanism by which neurons communicate. Action potentials are essential for the functioning of the nervous system, allowing for the transmission of signals over long distances within the body.
+An action potential is a fundamental feature of the [[nervous system]] and is essential for the propagation of signals along the [[axon]] of a [[neuron]]. It is a transient event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory.
-[[File:Neuron action potential.svg|thumb|right|Diagram of an action potential in a neuron.]]
+==Phases of an Action Potential==
-===Overview===
+===Resting Potential===
-Action potentials occur in the [[axon]]s of [[neurons]] and are initiated when a neuron receives a sufficient [[stimulus]] to depolarize its membrane to a critical threshold. This depolarization is followed by a rapid rise in membrane potential, a peak, and then a return to the resting potential.
+The [[resting potential]] is the baseline state of the neuron, typically around -70 mV. This is maintained by the [[sodium-potassium pump]] and the differential permeability of the membrane to [[sodium]] and [[potassium]] ions.
-===Phases of an Action Potential===
+===Depolarization===
+During depolarization, [[voltage-gated sodium channels]] open, allowing sodium ions to flow into the cell. This causes the membrane potential to become more positive.
-====Resting Potential====
+===Repolarization===
-The resting potential is the baseline state of a neuron, typically around -70 mV. This potential is maintained by the [[sodium-potassium pump]] and the differential permeability of the membrane to [[sodium]] and [[potassium]] ions.
+Repolarization occurs when the sodium channels close and [[voltage-gated potassium channels]] open, allowing potassium ions to flow out of the cell, returning the membrane potential to a negative value.
-====Depolarization====
+===Hyperpolarization===
-When a neuron is stimulated, [[voltage-gated sodium channels]] open, allowing sodium ions to rush into the cell. This influx of positive ions causes the membrane potential to become less negative, leading to depolarization.
+Hyperpolarization is a phase where the membrane potential becomes more negative than the resting potential. This is due to the continued efflux of potassium ions.
-====Repolarization====
+===Refractory Period===
-Following depolarization, [[voltage-gated potassium channels]] open, allowing potassium ions to flow out of the cell. This efflux of positive ions helps to return the membrane potential to a more negative value.
+The [[refractory period]] is a period of time during which a neuron is unable to fire another action potential. It consists of the absolute refractory period and the relative refractory period.
-====Hyperpolarization====
+==Propagation of Action Potentials==
-The membrane potential temporarily becomes more negative than the resting potential due to the continued efflux of potassium ions. This phase is known as hyperpolarization.
+Action potentials propagate along the axon of a neuron. In [[myelinated axons]], the action potential jumps between [[nodes of Ranvier]] in a process called [[saltatory conduction]]. This increases the speed of transmission.
-====Return to Resting Potential====
+==Role in Synaptic Transmission==
-The sodium-potassium pump and other ion channels restore the resting potential, preparing the neuron for the next action potential.
+Action potentials play a crucial role in [[synaptic transmission]]. When an action potential reaches the [[axon terminal]], it triggers the release of [[neurotransmitters]] into the [[synaptic cleft]], which then bind to receptors on the [[postsynaptic neuron]].
-===Propagation of Action Potentials===
+==Pacemaker Potentials==
-Action potentials propagate along the axon of a neuron. In myelinated axons, this propagation occurs via [[saltatory conduction]], where the action potential "jumps" from one [[node of Ranvier]] to the next, increasing the speed of transmission.
+[[Pacemaker potentials]] are spontaneous depolarizations that occur in certain types of cells, such as those in the [[sinoatrial node]] of the heart. These potentials are responsible for initiating the rhythmic contractions of the heart.
-[[File:Saltatory conduction.svg|thumb|left|Illustration of saltatory conduction in a myelinated axon.]]
+==Related pages==
-===Refractory Periods===
-The refractory period is a time during which a neuron is unable to fire another action potential. It consists of two phases:
-* '''Absolute refractory period''': No new action potential can be initiated, regardless of the strength of the stimulus.
-* '''Relative refractory period''': A stronger-than-normal stimulus is required to initiate an action potential.
-==Significance in the Nervous System==
-Action potentials are crucial for the functioning of the [[central nervous system]] and the [[peripheral nervous system]]. They enable the rapid transmission of signals necessary for [[muscle contraction]], [[sensory perception]], and [[cognitive processes]].
-==Related Pages==
 * [[Neuron]]
 * [[Synapse]]
-* [[Neurotransmitter]]
+* [[Myelin]]
 * [[Electrophysiology]]
-[[Category:Neuroscience]]
+==Gallery==
+<gallery>
+File:Action_Potential.gif|Animation of an action potential.
+File:Action_potential_basic_shape.svg|Basic shape of an action potential.
+File:Action_potential.svg|Graph of an action potential.
+File:Blausen_0011_ActionPotential_Nerve.png|Illustration of action potential in a nerve.
+File:Membrane_Permeability_of_a_Neuron_During_an_Action_Potential.svg|Membrane permeability during an action potential.
+File:SynapseSchematic_en.svg|Diagram of a synapse.
+File:Pacemaker_potential.svg|Graph of a pacemaker potential.
+File:Neuron1.jpg|Image of a neuron.
+File:Conduction_velocity_and_myelination.png|Conduction velocity and myelination.
+File:Cable_theory_Neuron_RC_circuit_v3.svg|Cable theory in neurons.
+File:Gap_cell_junction-en.svg|Gap junctions in cells.
+</gallery>
 [[Category:Electrophysiology]]
+[[Category:Neurophysiology]]