Flashcards in Nerve Impulses: Action Potential Deck (17):
What is an action potential?
A brief reversal of the potential across the membrane of a neurone causing a peak of +40mV compared to the resting potential of -60mV.
What is positive feedback?
A mechanism that increases a change taking the system further away from the optimum.
What is the resting potential?
The potential difference across the membrane while the neurone is at rest.
What does it mean if a neurone is at rest?
When a neurone is not transmitting an action potential.
Why is the membrane more permeable to potassium ions than to sodium ions?
The potassium ion channels are always open so allow the movement of potassium ions across the membrane. Whereas the gated sodium ion channels are kept closed.
What is another reason for the inside of the cell to remain negative?
The cell cytoplasm also contains large organic anions (negatively charged ions). Hence the interior of the cell at a negative potential compared with the outside.
What is the value for the resting potential?
How are the neurone's gated channels opened?
By the action of the synapse.
What happens when the gated channels open?
A few sodium ions enter the cell which produces a small depolarisation. This is known as a generator potential.
What are sodium gated channels also called?
How are voltage gated channels opened?
By slight changes in the potential difference of the membrane.
How are generator potentials an example of positive feedback?
As more generator potentials are created to reach a threshold potential they cause the voltage-gated channels to open. A small depolarisation of the membrane causes a change which increases the depolarisation further.
What happens as a result of the voltage-gated sodium ion channels opening?
It causes an influx of sodium ions and the depolarisation reaches =40mV. Once this value is reached the neurone will transmit the action potential.
What does "the action potential is self-perpetuating" mean?
Once it starts at one pouint in the neurone, it will continue along to the end of the neurone. They are therefore referred to as all or nothing responses.
What is the threshold value of the membrane before an action potential is created?
What is it called when the potential difference overshoots slightly?