1. Action Potentials

Question 1

What other channels open when neurone is stimulated?

Answer 1

Sodium ion channels open

If stimulus is big though it will trigger a rapid change in potential difference and membrane becomes depolarised

Question 2

The sodium ion channels are voltage gated, what does this mean ?

Answer 2

They only open when potential difference reaches a certain voltage

Question 3

1. Stimulus

Answer 3

Cell membrane becomes excited.

Sodium ion channels open and sodium ions diffuse down Sodium ion electrochemical gradient into the neuron as membrane is permeable to spildion ions

Inside less negotiable

Question 4

2. Depolarisation

Answer 4

Potential differences reaches threshold of around -55 mV

More sodium ion channels open

More sodium ions diffuse into neurone

Question 5

3. Repolarisation

Answer 5

When potential difference reaches + 30 mV the sodium ion channels close and potassium ion channels open.

Membrane becomes permeable to potassium ion channels so they diffuse down their conc gradient out of neurone - resting potential is restoring

Question 6

4. Hyperpolarisation

Answer 6

Potassium channels are slow to close leading to overshoot - too many potassium ions leave membrane.

The potential difference is lower than that of resting potential so less than -70 mV

Question 7

5. Resting potential

Answer 7

Ion channel resets

Sodium- potassium pump returns to normal pumping 2 potassium ions in and 3 sodium ions out

This resting potential is maintained until membranes excites by another stimulus

Question 8

During repolarisation why do sodium ion channels have to close ?

Answer 8

Or membrane will remain depolarised

Question 9

What is the refractionary period ?

Answer 9

After action potential neurone can’t be excited straight away against

Because ion channels are recoeverinr so can’t be made to open
Sodium ion channels closed during repolarisation and potassium ion channels closed during hyperpolarisation

Question 10

Why is the refractionary period important

Answer 10

Acts a time delay between one acfjo potential and the next

So no over lapping occurs

Also means there’s a limit to the frequency at which the nerve impulses can be transmitted and that action potentials are unidirectional

Question 11

Order of action Potential

Answer 11

Stimulus 
Depolarisation 
Repolarisation 
Hyperpolarisation 
Resting potential

Question 12

Waves of depolarisation

Answer 12

• action potential occurs and sodium ions diffuse into neurone
• some sodium ions move sideways in neurone into the next region which opens up sodium ions here allowing sodium ions to diffuse through that part
• generates waves or depolarisation

Question 13

What is the all or nothing principle ?

Answer 13

Once threshold has been reached an action potential will always fire same change in voltage no matter how big stimulus

If threshold isnt reached an action potential won’t fire

A bigger stimulus won’t cause bigger action potential but it will cause them to fire more frequently

Question 14

Why is all or nothing principle important

Answer 14

Stops brain from getting over stimulated by not responsive to very small stimuli