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A Level Biology - Unit5 > Nervous Transmission > Flashcards

Flashcards in Nervous Transmission Deck (20):

What is potential difference?

The difference in charge between the inside and outside of the axon.


What is the state of the axon membrane at resting potential?

The outside of the membrane is more positively charged than the inside of the axon.


What is the normal potential difference across a membrane?

Around -70mV


What 3 events happen that result in the creation of the resting potential?

1) 3 sodium ions are pumped out and 2 potassium ions are pumped in. This is done by a sodium potassium pump.
2) Na+ diffuse into the axon and K+ out of the axon (down an electrochemical gradient)
3) Most sodium gated channels are closed and potassium channels open so more K+ diffuse out, creating resting potential.


What is depolarisation?

A change in potential difference from negative to positive.


What is repolarisation?

A change in potential difference from positive back to negative.


Describe the sequence of events that occur during an action potential across an axon.

The steps are labelled in the next few cards.....


Step 1

Neurone has a resting potential. Some K+ ion channels are open. All Na+ voltage gated ion channels are closed.


Step 2

Energy of stimulus triggers some Na+ voltage gated ion channels to open. Na+ ions diffuse into axon.
Inside of neurone is less negative


Step 3

Change in charge causes more Na+ ion channels to open so more Na+ diffuse into axon.


Step 4

PD reaches +40mV.
Voltage gated sodium ion channels close.
Voltage gated potassium ion channels open.
Membrane is more permeable to K+ ions.


Step 5

Potassium ions diffuse out of axon
Inside of axon becomes more negative than outside.


Step 6

Hyperpolarisation occurs due to lots of K+ diffusing out.
Voltage gated potassium channels close.
Axon repolarises by the sodium potassium pump (pumping 3Na+ out and 2K+ in)


What is saltatory conduction?

Action potential jumps from one node of Ranvier to the next along he axon.


What two other factors affect speed of an impulse?

Axon diameter


How does axon diameter affect impulse speed?

Bigger diameter means less resistance to flow of ions in the cytoplasm.


How does temperature affect impulse speed?

Ions diffuse faster at higher temps.


If temperatures go above 40 degrees, how is the impulse affected?

The proteins in the axon membrane denature and the ions cannot be pumped in and out, therefore the impulse can go no further.


What is the all-or-nothing principal?

Only when the threshold value is reached can an action potential be created.


How does the size of a stimulus affect the action potentials?

Larger stimulus means more frequent action potentials are generated.
However the size of the action potential always stays the same.