Action Potential

Question 1

What is an action potential?

Answer 1

Change in voltage across a membrane

Question 2

What does an action potential depend on?

Answer 2

The ionic gradients

Relative permeability of the membrane

Question 3

What is the all or nothing principal?

Answer 3

Either will cause an action potential or not

There are no small or large action potentials

Question 4

What happens if the depolarisation reaches threshold?

Answer 4

Initiation of an action potential occurs at the axon hillock

Question 5

What do ion channels have to do with equilibrium potentials?

Answer 5

If more of a particular ion channel is open, the membrane potential will move closer to the equilibrium potential for that on
E.g. Na is +61, and if lots of Na channels open, membrane potential moves towards

Question 6

Which ion causes depolarisation?

Answer 6

Na

Large increase in Na permeability

Question 7

How much does an cation potential increase Na concentration by?

Answer 7

40 micro moles (very small)

Question 8

What are voltage clamps used for?

Answer 8

Measures membrane currents at set membrane potentials

Question 9

What pump is NOT involved in repolarisation of the action potential?

Answer 9

Na K ATPase pump

Question 10

What is the channel activity during an action potential?

Answer 10

Na channels open
Na moves in
Membrane depolarises
Na channels inactivate and k channels open
Na stops moving in but K still moves out
Membrane depolarises
Na channels open…

Question 11

What is the ARP?

Answer 11

Absolute refractory period

Nearly all Na channels are in the inactivated state

Question 12

What is RRP?

Answer 12

Relative refractory state
Na channels are recovering from inactivation
The excitability returns towards normal as the number of channels in inactivation decreases

Question 13

What is the basic structure of an Na channel?

Answer 13

Functional channel- 1 alpha subunit
Pore region- pore selectivity
Voltage sensor -voltage selectivity
May have inactivation particle

Question 14

What is the basic structure of a k channel?

Answer 14

Functional channel- 4 alpha subunits
Pore region- pore selectivity
Voltage sensor -voltage selectivity

Question 15

In what way do channels open and close?

Answer 15

Randomly

Question 16

How do anaesthetics work?

Answer 16

Block Na channels e.g. Procaine

Question 17

In what order to anaesthetics block?

Answer 17

Small myelinated neurones
Unmyelinated neurones
Large myelinated neurones

Question 18

What is a nerve fibre comprised off?

Answer 18

Several axons with different diameters

Question 19

What is a length constant?

Answer 19

The distance it takes for the potential to fall to 37% of its original value

Question 20

What is capacitance?

Answer 20

Ability to store charge

Question 21

What would a high capacitance of a membrane mean?

Answer 21

Voltage changes more slowly in response to current injection

Question 22

What would a high resistance of an axon mean?

Answer 22

Change in voltage spreads further along the axon (less ion channels open)

Question 23

What does the spread of local current depend on?

Answer 23

Membrane resistance and capacitance

Question 24

What is the myelin sheath good at?

Answer 24

Insultion

Question 25

What is saltatory conduction?

Answer 25

Action potential jumps from node to node allowing much faster conduction velocity
Action potentials only occur at the nodes

Question 26

How does the myelin sheath improve conduction?

Answer 26

Increase resistance
Decrease capacitance
Increase length constant
Decrease time constant

Question 27

What diseases affect conduction of the action potential?

Answer 27

MS
Devics disease 
Landry-guillain-barre syndrome
Charcot-Marie-tooth disease 
(Due to break down or damage of myelin sheath)

Question 28

What is demyelination?

Answer 28

Failure to reach the threshold as density of the action potential is reduced because of resistive and capacitive shunting

Question 29

How is a signal passed from nerve to muscle?

Answer 29

Neuromuscular junction

Question 30

What happens at a neuromuscular junction?

Answer 30

Action potential arrives
Ca channels open and Ca enters
Ca binds to synaptotagmin, vesicle is brought close to membrane and snare complex makes a fusion pore which transmitter leaves by
ACh binds to nicotinic receptors on the muscle end plate
These open channels and depolarisation of end plate occurs
Voltage gated Na channels open
Action potential initiates and muscle contracts

Question 31

Why is the concentration of Ca in nerve terminal being low mean?

Answer 31

Only needs a small increase in Ca to rise the Ca concentration significantly

Question 32

If increased frequency if action potentials to nerve terminal what does this mean?

Answer 32

More Ca channels open
More Ca in
High Ca concentration

Question 33

What are Ca channels similar too?

Answer 33

Na channels

Question 34

What are the properties of Ca channels?

Answer 34

Activate slower than Na Channels
Activate and inactivate
Ca channel inactivated is Ca dependent (increases intracellular concentration of Ca causes inactivation as when ba goes through less inactivation)

Question 35

What breaks down ACh?

Answer 35

Acetylcholine esterase

Question 36

What is curare?

Answer 36

Poison that causes paralysis

Blocks transmission between nerve and muscle

Question 37

What kind of blockers are there for neuromuscular junctions?

Answer 37

Competitive

Depolarising

Question 38

How can competitive blocker be overcome?

Answer 38

Increase concentration of ACh

Question 39

How does succinylcholine work?

Answer 39

Binds where ACh should bind and causes Na channels to inactivate

Question 40

What is mayasthenia gravis?

Answer 40

Autoimmune disease tragetting nACh receptors
Weakness- especially in exercise
Antibodies directed against the nAChR
Loss of function by complement mediated lysis and receptor degradation

Question 41

How do nicotinic and muscularinic ach receptors operate differently?

Answer 41

Nicotinic produce fast depolarisation as it is a ligand gated ion channel
Muscularinic produce a slower response as they are coupled with G proteins which cause a cascade