Resting and action potential Flashcards
Which two proteins in a neurone’s cell surface membrane are responsible for creating and maintaining the resting potential?
Sodium-potassium pumps and potassium ion channels
How is resting potential established?
Sodium-potassium pump moves sodium ions out of the axon, and potassium ions into the axon.
This causes a high concentration of sodium ions OUTSIDE the neurone and a high concentration of potassium ions INSIDE the neurone.
The membrane is permeable to potassium ions but not sodium ions.
Potassium ions diffuse out of the axon by facilitated diffusion.
The charge is more positive outside the membrane than inside.
Explain why sodium ions and potassium ions can only cross the axon membrane through protein channels.
They cannot pass through the phospholipid bilayer as they are charged and not lipid soluble.
Explain why ATP is needed for resting potential.
The sodium-potassium pump uses active transport to move sodium ions and potassium ions against the concentration gradient.
Explain how an action potential occurs.
Sodium ion channels open at the end of the neurone (usually the end at the receptor), sodium ions move into the axon by facilitated diffusion, if threshold is reached (approx. -55mV) voltage gated sodium ion channels open and sodium ions diffuse into the axon, further depolarising the membrane and causing even more sodium ion channels to open. The membrane potential reaches +40.
Explain how repolarisation occurs.
Voltage gated sodium ion channels close, voltage gated potassium ion channels open, the membrane is now more permeable to potassium ions. The potassium ions leave by facilitated diffusion down the concentration gradient. The membrane repolarises.
What is hyperpolarisation and what causes it?
The membrane becomes even more polarised than resting (lower than about -70mV) this is because the potassium ion channels are slow to close so too many potassium ions leave the neurone, making it more negative inside the cell.
Explain why not every stimulus causes an action potential.
The influx of sodium ions needs to reach a threshold potential before the voltage gated sodium ion channels open.
What are voltage gated ion channels?
Protein channels that open at a certain potential difference across the axon membrane.
What surrounds the axon of a myelinated neurone?
Schwann cells
What are nodes of Ranvier?
Gaps between Schwann cells
