Action Potentials Drive Nerve Impulses for Neural Communication
- A nerve impulse is a rapid electrical signal that travels along a neuron’s axon.
- This electrical nature arises from the movement of positively charged ions across the neuron’s membrane, creating a wave-like shift in the membrane potential known as an action potential.
- These signals enable neurons to communicate with each other and other cells, forming the basis of the nervous system.
Definition
Action Potential
The action potential is the rapid electrical signal generated when the neuron's membrane potential reaches a threshold.
- Action potentials are all-or-nothing events.
- They either occur fully or not at all, depending on whether a threshold potential is reached.
The Phases of an Action Potential
1. Resting Potential
- Before an action potential begins, the neuron is at resting potential.
- This is a stable state where the inside of the neuron is negatively charged compared to the outside, typically around $-70 mV$. $-70 mV$.
- This charge imbalance is maintained by:
- These pumps actively transport three sodium ions (Na⁺) out of the neuron for every two potassium ions (K⁺) pumped in, creating a net negative charge inside.
- The membrane is more permeable to K⁺ than Na⁺, allowing more K⁺ to leak out, further increasing the negative charge inside.
- Large, negatively charged proteins inside the neuron contribute to the overall negative charge.
Remember, the resting potential is maintained by active transport, which requires energy from ATP.
2. Depolarization
- When a stimulus reaches the neuron, voltage-gated sodium channels open, allowing Na⁺ ions to rush into the cell.
- This influx of positively charged ions reverses the charge imbalance, making the inside of the neuron positive relative to the outside.
- The influx of positively charged ions reverses the charge imbalance, making the inside of the neuron positive relative to the outside.
- The membrane potential rises from $-70 mV$ to about $+30 mV$.$-70 mV$ to about $+30 mV$.
- Imagine a crowd rushing into a stadium through open gates.
- The sudden influx of people changes the environment inside the stadium, just as the influx of Na⁺ ions changes the charge inside the neuron.
3. Repolarization
- Shortly after depolarization, the sodium channels close and voltage-gated potassium channels open.
- K⁺ ions diffuse out of the neuron, restoring the negative charge inside.
- The membrane potential returns to around $-70 mV$.
Think of repolarization as opening exit doors in the stadium, allowing people to leave and restore balance.
Common Mistake- Students often confuse the direction of ion flow during depolarization and repolarization.
- Remember, depolarization is caused by sodium influx, and repolarization by potassium efflux.
