Nerve Impulses & Action Potentials:
A nerve impulse is the temporary reversal of the electrical
potential difference of across the neurone membrane.
The resting potential is the p.d. across the neurone cell
membrane when the neurone is at rest, this is when the
neurone membrane is “polarised”.
The resting potential is approximately -70mV.
To achieve the resting potential:
o The phospholipid bilayer is impermeable to ions, so
sodium-potassium pumps must actively transport 3Na+
out for every 2K+ in (this requires ATP).
o Potassium is able to diffuse back out of the cell through
open channel proteins, however most sodium channels
are closed so they are unable to diffuse back in as quickly
as the potassium diffuse back out.
o The potassium ions diffuse down an electrochemical
gradient back out of the cell.
o The cytoplasm of the cell contains negatively charged ions
(e.g. on proteins) so the interior of the neurone is more
negative than the exterior.
o Generating the negative resting potential.
Channel proteins can be voltage gated or stimulus sensitive:
o Voltage gated channels open or close depending upon the
p.d. across the membrane. Changes in the ion
concentration will change to shape of the protein.
o Stimulus sensitive channels - for example, the Pacinian
corpuscles – when the receptor receives a stimulus (in
this case pressure from touch), some sodium channels
A nerve impulse is the temporary reversal of the electrical
potential difference of across the neurone membrane.
The resting potential is the p.d. across the neurone cell
membrane when the neurone is at rest, this is when the
neurone membrane is “polarised”.
The resting potential is approximately -70mV.
To achieve the resting potential:
o The phospholipid bilayer is impermeable to ions, so
sodium-potassium pumps must actively transport 3Na+
out for every 2K+ in (this requires ATP).
o Potassium is able to diffuse back out of the cell through
open channel proteins, however most sodium channels
are closed so they are unable to diffuse back in as quickly
as the potassium diffuse back out.
o The potassium ions diffuse down an electrochemical
gradient back out of the cell.
o The cytoplasm of the cell contains negatively charged ions
(e.g. on proteins) so the interior of the neurone is more
negative than the exterior.
o Generating the negative resting potential.
Channel proteins can be voltage gated or stimulus sensitive:
o Voltage gated channels open or close depending upon the
p.d. across the membrane. Changes in the ion
concentration will change to shape of the protein.
o Stimulus sensitive channels - for example, the Pacinian
corpuscles – when the receptor receives a stimulus (in
this case pressure from touch), some sodium channels
