the nerve impulse Flashcards
(31 cards)
What is the resting potential?
Potential difference across the membrane of axon when an impulse is not being transmitted
What is the value of the resting potential?
-70mV
What are all neurones when they have a resting potential?
Polarised so they are negatively charged with respect to outside the cell
What are the ion ratios in a polarised neurone?
More sodium ions on the outside of the cell and more potassium ions on the inside
How can the resting potential be maintained?
The membrane is differentially permeable - more potassium ion channels than sodium
What does this lead to?
A net loss of positive charged ions from the axon
What else is done to maintain a resting potential?
Sodium potassium pump actively transports ions against their diffusion gradients
What does this ensure?
An electrochemical gradient is maintained
What is an action potential?
When a receptor is stimulated above its threshold
What does an action potential involve?
A change in the potential across the axon membrane from a negative inside value
What is this known as?
Depolarisation
What is the value for the peak of the action potential?
+40mV
What does depolarisation result from?
An increase in permeability of the axon membrane as sodium channel proteins open
What happens to the sodium ions?
They move into the cell via diffusion
What does this cause?
More sodium ion channels to open
What happens to the value of the potential difference?
It increases and becomes positive as sodium ions move in
What happens when the membrane is fully depolarised?
Sodium ion channels close and potassium ion channels open
What happens to the potassium ions?
They diffuse out the axon
What does this begin the process of?
Repolarisation
Why is this?
The inside of the cell becomes less positive
How do all the ions become restored to resting potential?
The sodium potassium pump actively transports the ions
How is the action potential transmitted?
Along the axon as a nerve impulse or a wave of depolarisation
Why is this?
The sodium ions stimulate an increase in permeability in the next section of the axon
What is the refractory period?
Period after the formation of an action potential when a neurone cannot generate another action potential
