behaviroal lecture 2.10.25

Action Potential Overview

• Definition: The action potential is a rapid and temporary change in the membrane potential of a neuron, which allows for communication between nerve cells and the propagation of electrical signals.

Phases of Action Potential

1. Resting Potential

• State: Neurons at rest have a resting membrane potential around -70 mV.

• Ion Distribution: High concentration of sodium (Na+) outside the cell and potassium (K+) inside the cell.

2. Depolarization

• Trigger: When a stimulus reaches a threshold level (approximately -55 mV), voltage-gated Na+ channels open.

• Influx of Na+: Sodium ions rush into the neuron, causing the inside to become more positive.

3. Repolarization

• Closure of Na+ channels: When the membrane potential reaches around +30 mV, Na+ channels close.

• Opening of K+ channels: Potassium channels open, allowing K+ to flow out of the cell, restoring the negative charge.

4. Hyperpolarization

• State: The membrane potential temporarily becomes more negative than the resting potential (around -80 mV) due to excess K+ efflux.

• Return to Resting Potential: The neuron eventually returns to its resting state through the action of the Na+/K+ pump.

Key Concepts

• Threshold: The minimum membrane potential that must be reached for an action potential to occur (about -55 mV).

• All-or-Nothing Principle: If the threshold is reached, an action potential will occur; if not, it will not.

• Propagation: Action potentials travel along the axon through a process called saltatory conduction in myelinated fibers, increasing the speed of transmission.

Importance of Action Potentials

• Action potentials are essential for neural communication, allowing signals to travel quickly across long distances in the nervous system. They play a crucial role in muscle contractions and the functioning of the brain.