Action Potential in Neurons, Animation.

Summary

Neurons communicate by transmitting electrical signals known as action potentials. These signals travel along the axon after being triggered by incoming signals received at the dendrites. The action potential is a brief reversal of electrical charge across the cell membrane, involving the movement of sodium and potassium ions. As the neuron depolarizes and reaches a threshold, sodium channels open, followed by potassium channels, leading to the rise and fall of the membrane potential. This process propagates the signal in one direction, with periods of recovery, ensuring that neurons transmit clear, rapid signals to their targets.

Takeaways

• 😀 Neurons communicate through dendrites (incoming signals) and axons (outgoing signals), using nerve impulses or action potentials.
• 😀 A neuron is polarized at rest, with a typical resting membrane potential of about -70mV, meaning the inside is more negative than the outside.
• 😀 The sodium-potassium pump maintains concentration gradients across the cell membrane, with more sodium outside the cell and more potassium inside.
• 😀 Excitatory signals at dendrites cause sodium to flow into the neuron, depolarizing the cell and making the membrane voltage less negative.
• 😀 Depolarization spreads through the neuron towards the axon hillock, the trigger zone where action potentials are typically generated.
• 😀 Action potentials occur when the membrane voltage reaches a threshold of -55mV, opening voltage-gated sodium channels and allowing sodium influx.
• 😀 The rising phase of an action potential is driven by sodium influx, reversing the cell membrane's polarity from negative to positive.
• 😀 Potassium channels open more slowly, allowing potassium to exit the cell during the falling phase, which restores the membrane's original resting value.
• 😀 Hyper-polarization occurs when potassium continues to exit after the membrane potential returns to resting values, making the cell more negative temporarily.
• 😀 The refractory period, consisting of the absolute and relative refractory periods, prevents the neuron from firing again immediately after an action potential.
• 😀 The propagation of an action potential travels in only one direction along the axon due to the refractory properties of ion channels, ensuring unidirectional signaling.

Q & A

How do neurons communicate with each other?

Neurons communicate through their dendrites and axon. Incoming signals are received at the dendrites, while outgoing signals travel along the axon to the nerve terminal.

What is an action potential?

An action potential is a brief reversal of electric polarity across the cell membrane, allowing rapid electrical communication along the axon.

What is the resting membrane potential of a neuron?

The resting membrane potential of a neuron is typically about -70mV, meaning the inside of the cell is more negative compared to the outside.

What role does the sodium-potassium pump play in maintaining the resting membrane potential?

The sodium-potassium pump maintains concentration gradients by pumping sodium out of the cell and potassium into the cell, keeping the resting membrane potential stable.

How do excitatory signals affect the neuron?

Excitatory signals at the dendrites open ligand-gated sodium channels, allowing sodium ions to flow into the cell, which reduces the negative charge inside and depolarizes the cell.

What happens at the axon hillock when the neuron receives enough excitatory signals?

When the summation of excitatory signals reaches the axon hillock and is strong enough, it triggers the generation of an action potential.

What is the threshold value required to initiate an action potential?

The threshold value required to initiate an action potential is typically around -55mV.

What happens during the rising phase of an action potential?

During the rising phase, sodium channels open, allowing sodium ions to rush into the cell, which causes the inside of the cell to become more positive and further depolarizes the membrane.

What is hyperpolarization, and how does it occur?

Hyperpolarization is a negative overshoot that occurs when potassium ions continue to leave the cell after the action potential, causing the membrane potential to become more negative than the resting value.

Why does the action potential only propagate in one direction along the axon?

The action potential propagates in one direction due to the refractory period, where the part of the axon that just fired cannot respond to new stimulation, ensuring the signal moves only toward the nerve terminal.