Neuronal Excitability

Question 1

What will happen to a neurone when it is activated?

Answer 1

The membrane potential of the neurone will depolarise from the resting membrane potential.

Question 2

What is the relationship between the level of depolarisation and the strength of the stimulation applied?

Answer 2

They are proportional

Question 3

What is a graded depolarisation of the membrane?

Answer 3

A neurone’s membrane depolarising from the resting membrane potential.

Question 4

What determines how a neurone responds to electrical activation?

Answer 4

Whether or not a certain critical level of depolarisation is reached.

Question 5

What happens if the critical level of depolarisation is reached?

Answer 5

The neurone will generate an all or none event known as an action potential.

Question 6

What is the threshold level

Answer 6

The level of membrane potential where the graded depolarisation becomes an action potential.

Question 7

What is the most common threshold level

Answer 7

Different neurones have different threshold levels, but most neurones produce action potentials at around -65mV

Question 8

How long is the resting membrane potential maintained for?

Answer 8

Until the cell is either activated or inhibited.

Question 9

What happens to the movement of Na+ ions when the neurone is at rest?

Answer 9

Since the concentration of Na+ ions are higher in the extracellular environment the diffusion gradient makes it favourable for them to move into the intracellular environment.

Question 10

What happens to the movement of K+ ions when the neurone is at rest?

Answer 10

Since the concentration of K+ ions are lower in the extracellular environment the diffusion gradient makes it favourable for them to move out of the cell into the extracellular environment

Question 11

What happens to ion movement when the nerve cell is at rest

Answer 11

• Concentration gradient is in favour of K+ diffusing to the extracellular environment. This is prevented by negatively charged particles.
  Concentration gradient is in favour of Na+ moving into the intracellular environment
  -

Question 12

What is used to calculate the membrane potential at equilibrium for each of the ions

Answer 12

Nernst Equation NOT REQUIRED

Question 13

What is the equilibrium potential for Na+

Answer 13

+71MV

Question 14

What is the equilibrium potential for K+

Answer 14

-95MV

Question 15

How do ions affect the RMP

Answer 15

Na+ ions leak into the cell and K+ ions leak out of the cell.

Question 16

What maintains the ionic concentration gradient over time despite being electrogenic

Answer 16

Na, K ATPase

Question 17

What is the relationship between the amount of Na+ entering the cell and the amount of K+ leaving the cell

Answer 17

They are the same

Question 18

What does the permeability of K+ being much greater mean

Answer 18

The resting membrane potential is much closer to Ek-

Question 19

What is the relationship between Ecl and the RMP

Answer 19

They are very close as there is little Cl- ,movement

Question 20

What is the Goldman Hodgkin Katz (GHK)

Answer 20

A modification of the Nernst Equation which takes into account relative permeabilities of ions in question.

Question 21

What does initial entry of Na+ ions into the cell lead to

Answer 21

Depolarisation of the cell from RMP

Question 22

What will happen if the cell is depolarised enough to reach threshold potential

Answer 22

The cell will produce an unstoppable all or nothing event (action potential)

Question 23

What does this action potential cause

Answer 23

A Further, steeper depolarisation.

Question 24

What happens right after depolarisation

Answer 24

K+ channels open at the same time that Na+ ions are inactivated

Question 25

What does the opening and deactivating of the ion channels do

Answer 25

Causes a K+ efflux and stops the Na influx

Question 26

What does the efflux of K+ ions and no influx of Na + ions cause

Answer 26

repolarisation

Question 27

What happens in the hyperpolarisation phase

Answer 27

K+ continue to be activated and inactivation of Na+ ions is removed

Question 28

In the propagation of AP across the axon, what are the charges at the ends of the axon

Answer 28

Region where the AP is +ve
Region where AP is heading or has been is -ve

Question 29

What causes Na+ ions to diffuse along the inside of the axon

Answer 29

Attraction to the negative charge ahead

Question 30

What does the forward movement of Na+ plus cause

Answer 30

Depolarisation which triggers the opening of sodium voltage gated ion channels. This results in more Na+ entering the cell causing more depolarisation and an action potential

Question 31

What happens to the Na+ that diffuse backwards

Answer 31

They won’t cause an AP as this part of the axon is in its absolute refractory period and Na+ channels are inactivated

Question 32

What happens due to the myelin sheath insulating sections of the axon

Answer 32

Increases speed of AP conduction, also mean no leak of charge so SP can travel further

Question 33

Why do myelinated neurones transfer impulses faster than non-myelinated cells

Answer 33

Na+ ions only enter at the nodes of Ranvier causing depolarisation and an AP

Question 34

What is saltatory conduction

Answer 34

the AP jumping from one node to another by flow of ions

Question 35

Why can saltatory conduction speed up depolarisation across an axon

Answer 35

Every time channels open and close it takes time so reducing the number of places this happens saves time

Question 36

What is multiple sclerosis

Answer 36

A demyelinating disease

Question 37

Compare the conduction velocities of myelinated and non-myelinated neurones

Answer 37

0.1 metres/second Unmyelinated vs 100 metres/second myelinated

Question 38

How does the size of the axon affect the speed of conduction

Answer 38

The larger the diameter of the axon the faster the conduction.