Action Potential

Definition

An action potential is a rapid, transient change in the electrical membrane potential of a neuron, which allows for the transmission of signals along the nerve cell. This phenomenon is crucial for communication between neurons and ultimately enables the functioning of the nervous system, playing a significant role in both sensory processing and motor control.

5 Must Know Facts For Your Next Test

1. An action potential is initiated when the membrane depolarizes to a threshold level, typically around -55 mV, triggering voltage-gated sodium channels to open.
2. During an action potential, sodium ions rapidly enter the neuron, causing a spike in voltage that can reach up to +30 mV.
3. After the peak of the action potential, potassium channels open, allowing potassium ions to exit the cell and restore the negative membrane potential.
4. Action potentials are all-or-nothing events; once triggered, they propagate along the axon without diminishing in strength.
5. Myelination increases the speed of action potentials through saltatory conduction, where the impulse jumps from one node of Ranvier to the next.

Review Questions

• How does depolarization initiate an action potential and what role do ion channels play in this process?
  • Depolarization initiates an action potential when a neuron's membrane potential reaches a critical threshold. This occurs due to the opening of voltage-gated sodium channels, allowing sodium ions to flood into the neuron. This influx of positive charge causes further depolarization, creating a rapid change in electrical potential that constitutes the action potential.
• Explain how repolarization restores the resting membrane potential after an action potential.
  • Repolarization occurs immediately after an action potential peaks. During this phase, voltage-gated potassium channels open, allowing potassium ions to flow out of the neuron. This efflux of positively charged potassium ions helps restore the negative charge inside the cell, returning the membrane potential towards its resting state, typically around -70 mV.
• Analyze the significance of myelination on action potentials and how it affects neuronal communication.
  • Myelination significantly enhances the efficiency of action potentials by promoting saltatory conduction. In myelinated neurons, action potentials jump from one node of Ranvier to another rather than traveling continuously along the axon. This not only speeds up signal transmission but also conserves energy, making communication between neurons faster and more efficient. The presence of myelin is crucial for optimal nervous system function and impacts everything from reflexes to complex motor tasks.

Related terms

Resting Membrane Potential: The electrical potential difference across the neuronal membrane when the neuron is not actively sending a signal, typically around -70 mV.

Depolarization: The process during an action potential where the membrane potential becomes more positive, usually as a result of sodium ions rushing into the neuron.

Repolarization: The phase following depolarization in which the membrane potential returns to a negative value, primarily due to the efflux of potassium ions out of the neuron.