Describe the changes at the cell membrane of a neuron during an action potential.

At rest the membrane potential is -70mV.

This is due to the  Na+/K+ pump, which actively transports 3 Na+ ions out of the cell for every 2 K+ ions in.

Therefore there is a net negative charge inside the cell.

Four stages:

Depolarization; Repolarization;Hyperpolarization; Afterhyperpolarization.

Depolarization - triggered by another neuron. The membrane becomes more leaky to Na+, so Na+ diffuses into the cell down an electrochemical gradient. This makes the potential difference across the membrane become more positive. Eventually a Threshold potential of -55mV is reached, which activates the voltage-gated Na+ channels. These open and allow a lot of Na+ to enter the neuron.

Repolarization - at +30mV the voltage-gated Na+ channels close and the voltage-gated K+ channels open. K+ diffuses out of the cell through the open channels, causing the membrane potential to become more negative again.

Hyperpolarization - or the 'overshoot' is when the membrane potential becomes more negative than the resting potential, due to prolonged K+ efflux.

Afterhyperpolarization - restoring the resting membrane potential. At this point the membrane potential is too negative AND the ions (Na+ and K+) are on the wrong side of the membrane. The Na+/K+ pump works to restore the ions to their correct sides and a new action potential cannot be generated.

AN
Answered by Alex N. Biology tutor

10911 Views

See similar Biology A Level tutors

Related Biology A Level answers

All answers ▸

Explain the process of transcription in living cells


A wheat farmer uses fertiliser on his crop for several months. During this time the pond at the end of the field becomes covered in a thin green film and starts to smell. What process is responsible for this and how does it occur?


Describe the process of DNA replication.


Explain the process of phagocytosis


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning