Action potential generation
the plasma membrane of a neuron
separates the extracellular space from the intracellular space
sodium ions are found in high concentration
outside of the cell whereas potassium ions are found in high concentration
inside of the cell. Voltage-gated
sodium channels, sodium potassium ATP-ase pumps
and voltage-gated potassium channels
are found embedded in the plasma membrane of the neuron.
To initiate an action potential
a stimulus causes the wave a positive charge to reach
voltage-gated sodium channels on the neuron membrane. The increase in positive
charge
causes the voltage-gated sodium channels to open. Positively charged sodium ions
flood into the neuron following their concentration gradient
this causes the inside a membrane near to the open sodium channel to become
more positively charged
this process is the deep polarization of the cell membrane
The build up a positive charge on the inside of the membrane eventually causes
the voltage-gated
sodium channels to close. At the same time
voltage-gated potassium channels open since open only when the inside
remember is that maximum positive charge. Positively charged
potassium ions flow rapidly out of the neuron following their concentration
gradient this decreases the level of positive charge
on the inside surface of the neuron. This return of the membrane to resting
levels of negative
charge is called repolarization. Once
the region and the membrane has been fully repolarized, potassium
channels close
a sodium/potassium pump
uses ATP energy to restore the concentration gradient
and put potassium and sodium to the resting values
Let's summarize the processes of generating an action potential
resting potential is the membrane
potential of a neuron when it is at rest. The resting potential is well below
zero
to initiate an action potential the stimulus causes a slight depolarization
or increase in positive charge. If the stimulus is strong enough to cause the
membrane potential to reach a certain threshold
action potential will begin. In the rising phase of an action potential
wilted kid sodium channels open and sodium ions flow into the cell
this causes voltage to increase inside the cell
During the following phase of the action potential
voltage-gated sodium channels close, voltage-gate potassium channels open
the opening of the potassium channels causes potassium ions to diffuse out of the cell
rapidly
causing a sharp decrease in voltage. During the recovery phase
sodium potassium ATP-ase pump restores the resting potential
sodium potassium ATP-ase pumps
pump 2 sodium ions in and 3 potassium ions out
of the neuron. Sodium potassium ATP-ase pumps require ATP to function