Generation and Transmission of Action Potentials

Generation & Transmission of Action Generation & Transmission of Action
Potentials: potentials:
Resting Potential:
Some of the voltage-gated K+ channels are
open.
All the voltage-gated Na+ channels are
closed.
The Na-K pump actively transports 2K+ into
the cells & 3Na+ out of the cells.
The p.d. across the membrane is -70mV.
Stimulus:
When a stimulus arrives at the receptor/
nerve ending, it triggers the opening of
some Na+ stimulus sensitive channel
proteins.
+
Na diffuse down the electrochemical
gradient into the cell, causing the inside of
the cell to become more positive than the
outside.
If the stimulus is big enough,
depolarisation will occur.
Depolarisation:
If the p.d. of the membrane reaches the
threshold voltage (-50mV), the membrane
is said to be depolarised.
Voltage-gated sodium channels now open
& Na+ ions diffuse into the cell down the
electrochemical gradient.
As more Na+ diffuse in & the membrane
potential becomes more positive, more
voltage-gated Na+ channels open.
As the membrane potential becomes more
positive, voltage-gated K+ channels will
close, causing the membrane potential to
become even more positive.