How does a nerve transmit impulses?

At rest a nerve cell or fiber has more sodium (NA+) ions in the extracellular fluid and more potassium (K+) ions in the intracellular fluid. There are both NA+ and K+ ion channels in the membrane of the nerve cell and both are closed. Some of the K+ channels are a bit leaky and they let a small flow of k+ ions out of the nerve. This small flow causes the inside of the nerve to be more negative than the outside. We describe the cell as having a potential difference of -70mv. When stimulated to transmit an impulse NA+ channels in the membrane open, allowing NA+ to move into the cell down its diffusion gradient, this makes the inside of the cell less negative (more positive). This happens slowly until the cell reaches a threshold potential difference of -50mv. That is the cell has become sufficiently less negative. Once this threshold has been reached loads of NA+ channels open, allowing the ions to rush into the cell quickly causing the cell to become so much less negative it is positive, a potential difference of +40mv is reached. This positivity within the cell is known as depolarization and stimulates adjacent area of the nerve to also become positive, using the same mechanism. A wave of positivity (or depolarization) then spreads along the nerve, transmitting an impulse.

KW
Answered by Kay W. Biology tutor

2905 Views

See similar Biology A Level tutors

Related Biology A Level answers

All answers ▸

Describe the structure and function of a chemical synapse.


How does a mutation lead to a non-functional enzyme?


Explain 3 ways in which red blood cells are adapted to perform their function efficiently


How do auxins bring about positive phototropism in plants?


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