Action Potential (L4)

What is an action potential, and what is its main function?

A brief 1-2m reversal of the resting membrane potential used to transmit electrical signals.

What are two common synonyms for an action potential?

Nerve impulse and spike.

How do neurons encode information using action potentials?

Through the frequency and pattern of spikes (not their size).

Intracellular recording:

measures the potential difference between the tip of the electrode (inside the cell, i.e. intracellular) and the outside.

Extracellular recording:

electrode is close to the cell, but does not impale it = ground

Depolarize

Membrane potential moves closer to zero (less negative)

Polarized

Resting membrane potential

Hyperpolarize

Membrane potential moves away from zero (more negative)

Threshold

minimum amount of depolarization necessary to trigger action potential

Repolarization

changing membrane potential opens voltage-gated K+ channels

How is the short-lasting increase in the Na+ current accomplished?

Through the VOLTAGE-GATED SODIUM CHANNEL

What triggers the pore of a voltage-gated Na+channel to open?

Shift to a less negative membrane potential (depolarization).

How quickly do voltage-gated Na+ channels open, and how long do they stay open?

Open immediately and stay open for ~1 ms.

What condition must be met before a closed voltage-gated Na+ channel can reopen?

The resting membrane potential must be restored.

What do voltage-gated Na⁺ channels help explain?

The action potential (AP) threshold, rapid rising phase, brief duration, and absolute refractory period.

How do voltage-gated Na⁺ channels explain the AP threshold?

They are voltage-gated, meaning they open when the membrane reaches a certain voltage threshold.

Why does the AP have a quick rising phase?

Voltage-gated Na⁺ channels open rapidly, allowing Na⁺ to enter the neuron quickl

What causes the absolute refractory period?

Voltage-gated Na⁺ channels remain inactivated for about 1 ms, preventing another AP from starting immediately.

When do voltage-gated K⁺ channels open?

When the cell is depolarized.

What is an important characteristic of voltage-gated K⁺ channels?

They have about a 1 msec delay before opening.

How long do voltage-gated K⁺ channels stay open?

They stay open as long as the membrane is depolarized.

How do voltage-gated K⁺ channels cause the falling phase of the AP?

Their delayed opening allows K⁺ to leave the cell, causing the membrane potential to fall.

How do voltage-gated K⁺ channels cause the undershoot?

Increased K⁺ permeability moves the membrane potential closer to Eᴋ (the equilibrium potential for K⁺).