week 2 - Action Potentials

These flashcards cover key concepts related to action potentials and the sodium-potassium pump in neurons, providing a comprehensive review for physiology students.

Where does an action potential begin in a neuron?

At the axon hillock, where the threshold potential is first reached.

What is the resting membrane potential of a neuron?

Approximately –70 mV.

What ions maintain the resting membrane potential?

Sodium (Na⁺) and potassium (K⁺), regulated by the sodium-potassium pump.

What causes depolarization in a neuron?

The opening of voltage-gated sodium (Na⁺) channels, allowing Na⁺ to rush into the cell.

What happens during repolarization?

Voltage-gated sodium channels close, and potassium (K⁺) channels open, allowing K⁺ to exit the cell, restoring a negative charge.

What is hyperpolarization?

When too much K⁺ leaves the cell, making the membrane potential more negative than the resting potential.

What is the threshold potential needed to trigger an action potential?

Around –55 mV.

What is the refractory period?

The time after an action potential when a neuron cannot fire another action potential.

What are the two phases of the refractory period?

Absolute refractory period (no new AP can occur) and relative refractory period (a stronger stimulus needed to trigger AP).

How does myelination affect action potential conduction?

It increases conduction speed through saltatory conduction, where impulses jump between nodes of Ranvier.

What is saltatory conduction?

The jumping of action potentials between myelinated segments (nodes of Ranvier), speeding up transmission.

What ion channels open during depolarization?

Voltage-gated sodium (Na⁺) channels.

What ion channels open during repolarization?

Voltage-gated potassium (K⁺) channels.

What causes the inside of the neuron to become positive during depolarization?

Influx of sodium ions (Na⁺) into the cell.

What happens to sodium channels during the refractory period?

They become inactivated and cannot reopen immediately.

What is the “all-or-nothing” principle?

Once the threshold is reached, an action potential always occurs with the same magnitude; it doesn’t vary in size.

How are neurotransmitters released at the synapse?

Action potentials trigger calcium (Ca²⁺) entry at the axon terminal, causing vesicles to release neurotransmitters.

What is the main function of the sodium-potassium pump (Na⁺/K⁺ ATPase)?

To maintain the resting membrane potential by actively transporting Na⁺ out and K⁺ into the cell.

How many sodium ions are pumped out per cycle?

Three sodium (Na⁺) ions.

How many potassium ions are pumped in per cycle?

Two potassium (K⁺) ions.

Why is the sodium-potassium pump important for neurons?

It restores ion balance after action potentials and maintains the negative resting potential.

What enzyme drives the sodium-potassium pump?

ATPase.

How does the pump contribute to membrane potential?

It helps maintain a more negative interior by exporting more positive ions (Na⁺) than it imports (K⁺).

How does the sodium-potassium pump differ from sodium or potassium channels?

Channels allow passive diffusion; the pump uses ATP to actively move ions.

What maintains the high intracellular K⁺ (potassium) concentration?

The sodium-potassium pump continually transports K⁺ into the cell.

What maintains the low intracellular Na⁺ (sodium) concentration?

The pump exports Na⁺ out of the cell continuously.

Why is ATP needed for the sodium-potassium pump?

Because ions are moved against their electrochemical gradients, which requires energy.

When is the sodium-potassium pump most active?

After repeated firing of action potentials, when ion gradients need to be restored.

What happens to the pump when ATP is depleted?

Ion gradients collapse, and the neuron cannot maintain resting potential or fire action potentials.

Which side of the membrane has more sodium at rest?

The outside of the neuron.

Which side of the membrane has more potassium at rest?

The inside of the neuron.

What would happen to the resting membrane potential if K⁺ channels were blocked?

The neuron would depolarize because K⁺ could not exit, reducing negative charge inside.