The Action Potential And Conduction Of The Nervous Impulse

Question 1

Define an action potential

Answer 1

Change in voltage across membrane

Question 2

What what is the conductance of a membrane dependant on ?

Answer 2

The number of channels for the ion that are open

Question 3

How can we experimentally show that Na+ is responsible for depolarisation of cell membrane ?

Answer 3

If you decrease the concentration of Na+ outside the cell , then action potential peak decreases which suggests that the upstroke of action potential due to large increase in permeability to Na+

Question 4

How is the upstroke of an action potential an example of positive feedback ?

Answer 4

• once- when a stimulus is detected , Na+channels open which causes Na+ to enter the membrane. If threshold potential is met , this causes voltage gated Na+ channels to open which causes even MORE Na+ to enter the membrane.

Question 5

Do the amount of ions that move during an action potential produce a relatively large change in the membrane potential or small ?

Answer 5

SMALL

Question 6

What is voltage clamping ?

Answer 6

• an experimental method used to measure membrane currents over a set membrane potential.

Question 7

When voltage gated Na+ channels open during depolarisation what are they trying to reach / meet ?

Answer 7

They are moving in order to meet equilibrium Na+ which is around +80/+70.

Question 8

What causes depolarisation ?

Answer 8

• Voltage gated sodium channels opening ( or Ca2+)

Question 9

What causes repolarisation?

Answer 9

• opening of voltage gated K+ channels

Question 10

What causes hyperpolarisation

Answer 10

Opening of K+ channels

• delay in how long it takes to close

Question 11

What is the absolute refractory period and when does it occur ?

Answer 11

• channels are inactivated ( eg sodium).
• no matter how big a stimulus is , an action potential cannot be generated.
• occurs from depolarisation and repolarisation

Question 12

What is the relative refractory period and when does it occur ?

Answer 12

• channels are closed and require a very strong stimulus in order for an action potential to be generated.

Question 13

What does depolarisation of a membrane initiate ?

Answer 13

Nav channels inactivate and Kv channels open.

Question 14

In what order do local anaesthetics block ?

Answer 14

1) small myelinated axons
2) un-myelinated axons
3) large myelinated axons

Question 15

What does the local current theory state ?

Answer 15

• injection of a current into an axon will cause charge to spread and give immediate local change in membrane potential.

Question 16

What is the effect of a axon

diameter on transmission speed ?

Answer 16

• greater axon diameter would lead to faster transmission speed

Question 17

What is the propagation of axon potentials dependant on ( 2 factors )?

Answer 17

1) CAPACITANCE- the lower the capacitance the Better

2) MEMBRANE RESISTANCE - the greater the membrane resistance the better

Question 18

Define capacitance

Answer 18

• the ability to store charge
• it is the number of ions that are required to move through the membrane to get a voltage change to occur.
• this is a property of the lipid bilayer
• a low capacitance is needed for faster transmission because this means that voltage changes occurs more quickly.

Question 19

Why is a high membrane resistance required for the propagation of an action potential ?

Answer 19

Ask tutor

Question 20

What is saltatory conduction ?

Answer 20

• aNa-Na+ channels are only present in the nodes of ranvier.

- action potential jumps from one node to another node allowing much faster conduction velocity.

Question 21

How does myelin sheath improve conduction ?

Answer 21

1) large increase in membrane resistance
2) large decrease in membrane capacitance
3) increase in length constant
3) decrease in time constant

Question 22

What is the most common demyelinating disease ?

Answer 22

• multiple sclerosis which affects the nervous system.