nerones

Question 1

what do neurone cell membranes become at rest

Answer 1

polarised

Question 2

what happens to the outside of a neurone in its resting state

Answer 2

In a neurone’s resting state (when it’s not being stimulated), the outside
of the membrane is positively charged compared to the inside. This is
because there are more positive ions outside the cell than inside.

Question 3

what does it mean if the membrane is polarised

Answer 3

So the membrane is polarised — there’s a difference in charge
(called a potential difference or voltage) across it.

Question 4

what is the voltage across the membrane called when its at its resting state

Answer 4

resting potential — it’s a b o u t- 70 mV (millivolts).

Question 5

what is the resting potential of a voltage across the membrane created and maintained by

Answer 5

The resting potential is created and maintained by sodium-potassium pumps
and potassium ion channels in a neurone’s membrane:

Question 6

what do the sodium potassium pumps do

Answer 6

The sodium-potassium pumps move sodium ions out of the neurone,
but the membrane isn’t permeable to sodium ions, so they can’t
diffuse back in. This creates a sodium ion electrochemical gradient
(a concentration gradient of ions) because there are more positive
sodium ions outside the cell than inside

The sodium-potassium pumps also move potassium ions in to
the neurone, but the membrane is permeable to potassium ions
so they diffuse back out through potassium ion channels.
• This makes the outside of the cell positively charged compared to the inside

Question 7

how do sodium potassium pumps do what they do

Answer 7

These pumps use active transport
to move there  sodium ions  (Na 
out of the neurone for every two
potassium ions (K +) moved in.
A T P is needed to do this.

Question 8

what are potassium ion channels

Answer 8

Th ese channels allow facilitated
diffusion of potassium ions
(K +) out of the neurone, down
their concentration gradient.

Question 9

what happens when neurone cell membranes become stimulated

Answer 9

they become depolarised

Question 10

what does a stimulus trigger

Answer 10

A stimulus triggers other ion channels, called sodium ion channels, to open. If the stimulus is big enough, it’ll
trigger a rapid change in potential difference

Question 11

what are all the steps of action potential in order

Answer 11

1. stimulus
2. depolarisation
3. repolarisation
4. hyperpolarisation
5. resting potential

Question 12

what happens in the first step of action potential: stimulus

Answer 12

this excites the neurone
cell membrane, causing sodium ion
channels to open. The membrane
becomes more permeable to
sodium, so sodium ions diffuse into
the neurone down the sodium ion
electrochemical gradient. This makes
the inside of the neurone less negative

Question 13

what happens in the second step of action potential: depolarisation

Answer 13

if the potential
difference reaches the threshold
(around -55 mV), more sodium ion
channels open. More sodium ions
diffuse rapidly into the neurone.

Question 14

what happens in the third step of action potential: repolarisation

Answer 14

.at a potential difference of around + 30 mV the sodium ion
channels close and potassium ion channels open. The membrane is more permeable
to potassium so potassium ions diffuse out of the neurone d own the potassium ion
concentration gradient. This starts to get the membrane back to its resting potential.

Question 15

what happens in the fourth step of action potential : hyper polarisation

Answer 15

potassium ion channels are slow to close so there’s a slight
‘overshoot’ where too many potassium ions diffuse out of the neurone. The potential
difference becomes more negative than the resting potential (i.e . less than - 70 mV).

Question 16

what happens in the fifth step of action potential : resting potential

Answer 16

the ion channels are reset. The sodium-potassium pump returns the membrane
to its resting potential and maintains it until the membrane’s excite d by another stimulus

Question 17

what cant the neurone cell membrane be after an action potential

Answer 17

After an action potential, the neurone cell membrane can’t be excited again straight away. This is because the ion
channels are recovering and they can’t be made to open — sodium ion channels are closed during repolarisation and
potassium ion channels are closed during hyperpolarisation. This period of recovery is called the refractory period.

Question 18

what does the action potential move along

Answer 18

The Action Potential Moves Along the Neurone as a Wave of Depolarisation

Question 19

what are all the steps of Action Potential Moving Along the Neurone as a Wave of Depolarisation

Answer 19

1) W hen an action potential happens, some of the sodium ions that enter the neurone diffuse sideways.
2) This causes sodium ion channels in the next region of the neurone to open and sodium ions diffuse into that part.
3) This causes a wave of depolarisation to travel along the neurone.

4) The wave moves away from the parts of the membrane in the refractory period because these parts can’t fire an
action potential.

Question 20

what does the refractory period produce

Answer 20

The Refractory Period Produces Discrete Impulses

Question 21

during the refractory period what happens to the ion channels

Answer 21

During the refractory period, ion channels are recovering and can’t be opened

Question 22

what does the refractory period act as

Answer 22

So the refractory period acts as a time delay between one action potential and the next.
This means that:

• action potentials don’t overlap, but pass along as discrete (separate) impulses.
• there’s a limit to the frequency at which the nerve impulses can be transmitted.
• action potentials are unidirectional (they only travel in one direction).

Question 23

what happens once the threshold is reached

Answer 23

O n c e the threshold is reached, an action potential
will always fire with the same change in voltage,
no matter how big the stimulus is

Question 24

what happens if the threshold isn’t reached

Answer 24

If the threshold isn’t reached, an action potential won’t fire. A
This is the all-or-nothing nature of action potential

Question 25

what will a bigger stimulus not cause

Answer 25

A bigger stimulus won’t cause a bigger action potential,

but it w ill cause them to fire more frequently.