Action potential

Definition

An action potential is a rapid and transient electrical signal that travels along the membrane of a neuron, allowing it to communicate information to other neurons or muscles. This process involves changes in membrane potential that result from the movement of ions across the neuron's membrane, playing a crucial role in transmitting signals throughout the nervous system.

5 Must Know Facts For Your Next Test

1. An action potential typically starts when a neuron reaches a threshold level of depolarization, usually around -55 mV, leading to a rapid influx of sodium ions.
2. During an action potential, the membrane potential rapidly shifts from a resting state of around -70 mV to a peak of approximately +30 mV due to sodium ion channels opening.
3. Following the peak of the action potential, potassium channels open, allowing potassium ions to exit the cell, which helps to repolarize and eventually hyperpolarize the membrane.
4. The action potential is an all-or-nothing event; if the threshold is not reached, no action potential occurs.
5. Refractory periods follow an action potential, during which the neuron cannot fire another action potential immediately, ensuring directional signal propagation along the axon.

Review Questions

• How do changes in ion permeability contribute to the generation and propagation of an action potential?
  • Changes in ion permeability are crucial for generating and propagating an action potential. When a neuron receives a stimulus, sodium channels open, causing an influx of sodium ions that depolarizes the membrane. Once the threshold is reached, this depolarization triggers more sodium channels to open in a positive feedback loop, leading to the rapid rise of the action potential. After reaching its peak, potassium channels then open, allowing potassium ions to flow out and repolarize the cell. This sequential opening and closing of ion channels are essential for the signal to travel along the axon.
• Discuss how synaptic transmission relies on action potentials and their influence on neurotransmitter release.
  • Action potentials play a pivotal role in synaptic transmission by triggering the release of neurotransmitters at the synapse. When an action potential reaches the axon terminal, it causes voltage-gated calcium channels to open, allowing calcium ions to enter the terminal. This influx of calcium ions stimulates synaptic vesicles to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft. The binding of these neurotransmitters to receptors on the postsynaptic neuron can lead to further action potentials or inhibitory signals, depending on the nature of the neurotransmitter.
• Evaluate how integrate-and-fire models simulate the behavior of real neurons with respect to action potentials.
  • Integrate-and-fire models simulate neuronal behavior by representing how neurons integrate incoming signals and generate action potentials. These models consider both excitatory and inhibitory inputs that influence the neuron's membrane potential over time. Once a critical threshold is achieved through integration of these inputs, an action potential is generated. These simplified models capture essential features of neuronal dynamics, such as frequency coding based on input intensity and temporal summation of signals, while providing insights into how real neurons might process information and respond to stimuli.

Related terms

Resting potential: The electrical charge difference across the neuronal membrane when a neuron is not actively firing, typically around -70 mV.

Synapse: The junction between two neurons where neurotransmitters are released to transmit signals from one neuron to another.

Threshold:

The critical level of depolarization that must be reached for an action potential to be triggered in a neuron.