transmitting an impulse - resting potential

Concentration gradients across the membranes of the exon are established by [blank_start]sodium-potassium[blank_end] which pump [blank_start]3[blank_end]Na+ out and 2[blank_start]K+[blank_end] in

A negative charge inside the axon is also caused by the following negative molecules:

This continues until there is [blank_start]no[blank_end] difference in charge across the [blank_start]axon membranes[blank_end]

[blank_start]Potassium[blank_end] ions diffuse out of the neurone down the [blank_start]pottasium[blank_end] concentration gradient

This makes the inside of the axon more [blank_start]negative[blank_end] and the outside more [blank_start]positive[blank_end]

Some [blank_start]sodium[blank_end] moves into the axon down the [blank_start]sodium[blank_end] concentration gradient but the membrane is not very permeable to [blank_start]sodium[blank_end], unlike [blank_start]potassium[blank_end], so this amount is [blank_start]small[blank_end]

The diffusion of [blank_start]sodium[blank_end] makes [blank_start]no[blank_end] difference to the charge across the membrane. The diffusion of [blank_start]potassium[blank_end] out of the axon is the cause of a potential difference of [blank_start]-70[blank_end]mV across the membrane. This charge is [blank_start]stable[blank_end] because the [blank_start]electrochemical[blank_end] gradient goes from the outside to the inside of the axon whereas the [blank_start]potassium[blank_end] gradient goes from the inside of the axon to the outside. Sodium cannot interfere due to the [blank_start]impermeability[blank_end].

You can now describe the axon as p[blank_start]olarised[blank_end]

To summarise: a resting potential has a potential difference across the membrane of [blank_start]-70[blank_end]mV. This is caused by the movement of sodium and potassium. First, sodium is moved [blank_start]out[blank_end] whilst potassium is moved [blank_start]in[blank_end]. Next, [blank_start]potassium[blank_end] moves out too. After that, [blank_start]potassium[blank_end] moves back in. At this stage, the e[blank_start]lectrochemical[blank_end] gradient and potassium concentration gradient balance each other. The axon is [blank_start]polarised[blank_end].