Action potential

Question 1

What exactly is an impulse?

Answer 1

A change in the membrane potential (difference in charge inside vs outside) of a neurone which is sent along the length of the whole neurone
In other words, the action potential passing along the length of a neurone

Question 2

What is the action potential?

Answer 2

The change in potential over the membrane of a neuron that occurs (from rest) when a stimulus is detected in order to send an impulse down the neurone

Question 3

What do generator potentials depend on?

Answer 3

Voltage-gated sodium ion channel proteins
Voltage-gated potassium ion channel proteins causes changes in permeability——–> Depolarisation ——-> Action potential

Question 4

Are the voltage gated ion channel proteins closed at resting potential?

Answer 4

Yes both of them are

Question 5

Depolarisation

Answer 5

When a membrane potential becomes less negative (the neg charge inside is no longer as neg relative to the outside of a neurone before)
Or even positive (the inside of a neurone is now more positive relative the the outside)

Question 6

Depolarising generator potential at receptor

Answer 6

This occurs at start when a stimulus is detected, Na+ ions can enter the neurone (eg down stretch mediated channel protein) increasing pos charge inside the neurone

Question 7

Threshold value

Answer 7

The minimum amount of Na+ ions that enter neurone from stimulation detected by receptor to generate an action potential

Question 8

What happens if the threshold value is reached?

Answer 8

Voltage gated sodium ion channel proteins will rapidly open
So Na+ ions (at high conc outside) can rapidly diffuse into neurone down electrochemical grad using these membrane proteins

Question 9

What happens when Na+ ions can diffuse into neurone us8ng the voltage gated Na+ ion protein?

Answer 9

The neurone is further depolarised- the charge difference between neurone to the outside becomes positive as Na+ ions enter the neurone

Question 10

Peak membrane potential reading of depolarisation

Answer 10

+40mV

Question 11

What happens once the peak voltage reading for depolarisation happens?

Answer 11

The voltage gated sodium ion channel proteins close
And triggers opening of potassium ion channel proteins to open

Question 12

What happens when voltage gated potassium ion channel proteins open?

Answer 12

The potassium ions at high concentration in the neurone can diffuse out of the neurone to lose positive charge in neurone so it becomes negative again

Question 13

Depolarisation

Answer 13

Facilitated diffusion of potassium ions out of neurone over the neurone cell membrane using voltage gated potassium ion channel proteins to restore negative charge inside the neurone

Question 14

Hyperpolarisation

Answer 14

So many K+ ions leave neurone during repolarisation through voltage gated K+ channel proteins so membrane potential is more negative than resting potential

Question 15

What happens when hyperpolarisation is reached?

Answer 15

Voltage gated potassium ion channel proteins close so no more K+ ions can leave neurone membrane
So Na+K+pump protein can pump 3 Na+ ions out/K+ ions to restore resting potential, etc

Question 16

All or nothing principle

Answer 16

An action potential is only generated if a threshold stimulation is reached
For every given neurone: the generation of an action potential will always be the same size

Question 17

How can we encode for the strength of a stimulus if the strength of an action potential will always be the same?

Answer 17

By frequency of action potentials in a given time

Question 18

A very strong stimulus…

Answer 18

First: threshold stimulation is reached and exceeded to cause depolarisation of a neurone
Generated very frequent action potentials so strong stimuli

Question 19

If no threshold is reached…

Answer 19

Not enough Na+ ions enter neurone to trigger opening of voltage gated Na+ channel proteins
So no depolarisation
No action potential

Question 20

Why do we have a threshold?

Answer 20

Because if even very weak stimuli could generate an action potential then our nervous system would be very overwhelmed
Threshold allows filtering out of very weak stimuli

Question 21

How can the brain detect stimulus strength?

Answer 21

Different neurones have different threshold potentials so can be activated by stimulus of different strengths
To determine the strength of a stimulus, the brain can detect the relative number of different neurones to determine the strength of this stimulus

Question 22

What affects the nerve impulse (action potential) travelling down the neurone?

Answer 22

If neurone is myelinated with Schwann cells or not
Axon diameter
Temperature