Action Potentials and Repolarization

Hyperpolarization

A stimulus opens gated potassium ion channels, moving the membrane voltage below the resting potential value

(more negative than the resting potential)

Repolarize

The membrane potential is moving from a more positive value towards resting membrane potential

Depolarize

The membrane potential is becoming more positive than the resting membrane potential

Charge outside the cell is:

Always positive with the exception of the action potential

Action potential charge inside the neuron

Positive

Resting potential sodium (Na) location

Outside the cell

Resting potential potassium (K) location

Inside the cell

In depolarization sodium:

Starts entering the cell

In depolarization potassium:

Starts leaking out of the cell

During an action potential, sodium:

Enters the cell through Na channels

During an action potential, potassium:

Leaves the cell through K channels

In repolarization, sodium is:

Inside the cell, then pumped out by the sodium-potassium pump

In repolarization, potassium is:

Outside the cell, then pumped in by the sodium-potassium pump

Polarized

Ions are unequally distributed on either side of the cell’s membrane

How is the conduction of a nerve impulse started?

A stimulus (created by a neurotransmitter) changes the permeability of the cell’s plasma membrane. Then, sodium floods in and changes the cell’s polarity (depolarization)

How is an action potential generated?

a strong stimulus causes strong sodium ions to enter the cell

Steps in nerve impulse transmission

Resting potential → Depolarization → Peak → Repolarization → Hyperpolarization (small dip)