Action Potential

Definition

An action potential is a rapid, temporary change in the electrical charge of a neuron’s membrane, which allows it to transmit signals along its length and communicate with other neurons. This process is crucial for neural communication, enabling the propagation of information throughout the nervous system, influencing how sensory information is processed and integrated.

5 Must Know Facts For Your Next Test

1. Action potentials occur when a neuron's membrane depolarizes to a threshold level, typically around -55 mV, causing voltage-gated sodium channels to open and allowing sodium ions to rush into the cell.
2. After reaching its peak, an action potential quickly repolarizes as potassium channels open, allowing potassium ions to flow out of the neuron, restoring the negative internal charge.
3. The all-or-nothing principle states that once the threshold is reached, an action potential will occur; there are no partial action potentials.
4. Refractory periods follow an action potential, during which the neuron cannot fire another action potential until it returns to its resting state.
5. Action potentials are propagated along unmyelinated axons through continuous conduction and jump between nodes of Ranvier in myelinated axons through saltatory conduction, making signal transmission faster.

Review Questions

• How does the change in membrane potential during an action potential lead to signal transmission in neurons?
  • The change in membrane potential during an action potential starts with depolarization when sodium channels open and sodium ions enter the neuron, making the inside more positive. This rapid change allows the action potential to propagate along the axon. As the action potential moves, it triggers nearby voltage-gated channels to open, creating a wave-like effect that transmits the signal down the length of the neuron.
• In what ways do myelin sheaths affect the speed of action potential transmission?
  • Myelin sheaths significantly enhance the speed of action potential transmission by insulating axons and preventing ion leakage. This insulation allows action potentials to jump from one node of Ranvier to another in a process called saltatory conduction. As a result, myelinated axons can transmit signals much faster than unmyelinated ones, improving overall neural communication efficiency.
• Evaluate the importance of refractory periods following an action potential in neuronal signaling.
  • Refractory periods play a critical role in ensuring that action potentials are discrete events rather than continuous signals. The absolute refractory period prevents another action potential from occurring immediately after one has fired, allowing neurons time to reset their ion concentrations. The relative refractory period allows for increased stimulation before firing again, which helps regulate signal frequency and prevents excessive firing that could lead to neuronal damage or dysfunction.

Related terms

Resting Potential: The resting potential is the stable, negative charge of a neuron when it is not actively sending signals, typically around -70 mV.

Synapse: A synapse is the junction between two neurons where neurotransmitters are released to facilitate communication between them.

Myelin Sheath: The myelin sheath is a fatty layer that surrounds and insulates some axons, speeding up the transmission of action potentials.