Action Potential and Resting Potential

The process of nerve impulse conduction involves complex changes in the neuron's membrane potential. This page explains the resting state of neurons and the generation of action potentials.

Resting Potential

Neurons maintain a resting potential when not actively transmitting signals. This state is characterized by an imbalance of ions across the cell membrane.

Definition: The resting potential is the difference in electrical charge between the inside and outside of a neuron when it's not transmitting a signal, typically around -70mV.

Key features of the resting state include:

• Sodium-potassium pumps actively remove sodium ions from the cell cytoplasm.
• Potassium ions diffuse out of the cell through ion channels, following their concentration gradient.
• The balance of forces on potassium ions results in no net movement at the resting potential.

Highlight: The resting membrane potential is maintained by the balance between active ion pumping and passive ion diffusion.

Action Potential

When a neuron is stimulated, it can generate an action potential, which is the basis of nerve impulse conduction.

The stages of an action potential are:

1. Depolarization: Stimulation causes sodium channels to open, allowing sodium ions to enter the neuron. This makes the inside of the cell less negative.

2. Threshold: When the membrane potential reaches about -55mV, more sodium channels open, rapidly depolarizing the cell to about +30mV.

3. Repolarization: Sodium channels close and potassium channels open. Potassium ions leave the cell, restoring the negative charge inside.

4. Hyperpolarization: A brief period where the cell becomes more negative than its resting state due to the delayed closing of potassium channels.

5. Return to Resting State: The sodium-potassium pump helps restore the original ion concentrations.

Vocabulary: The refractory period is a short time after an action potential when the neuron cannot be excited again, ensuring that signals travel in one direction only.

Example: An action potential travels along an axon like a wave. As one area depolarizes, it triggers depolarization in the adjacent region, propagating the signal.