Local Anaesthetics: Membrane Potentials

Question 1

What concentration is intracellular fluid?

Answer 1

Negative

Question 2

What concentration is extracellular fluid?

Answer 2

Positive

Question 3

What direction does sodium want to move in?

Answer 3

Into the cell

Question 4

What direction does potassium want to move in?

Answer 4

Out of the cell

Question 5

What ions are in high concentration outside of the cell? (extracellular)

Answer 5

Sodium (Na)

Chlorine (Cl)

Question 6

What ions are in high concentration in the cell? (intracellular)

Answer 6

Potassium (K)

Question 7

What ion is the RESTING membrane permeable to?

Answer 7

K - potassium

Question 8

What creates the resting potential?

Answer 8

Passive movement of Potassium leaving the cell creates a negative charge intracellularly.

The active Na/K pump also contributes by moving 3 Na out and 2 K in. ( remember TOUCAN for resting potential)

Question 9

What are the range of values for the resting potential?

Answer 9

20 - 90 mV

Question 10

What are the two types of ion channels?

Answer 10

Voltage gated

Ligand gated

Question 11

Can ion channels have more than one gate?

Answer 11

Yes

Question 12

How many gates does a Na channel have?

Answer 12

2

Question 13

What are the two gates on a Na gated ion channel?

Answer 13

M gate

H gate

Question 14

How many gates does a K channel have?

Answer 14

1

Question 15

When the Na channel is closed, what are the conformations of both the M and H gate?

Answer 15

M gate closed

H gate open

Question 16

When the Na channel is open, what are the conformations of both the M and H gate?

Answer 16

M gate open

H gate open

Question 17

When the Na channel is closed for the REFRACTORY period, what are the conformations of both the M and H gate?

Answer 17

M gate open

H gated closed

Question 18

Describe the firing of an action potential.

Answer 18

Resting potential = 70mv

Stimulus occurs

Na moves inwards depolarising the cell toward the threshold

Once the threshold is reached at -55mv Na channels open and there is an influx of Na (further depolarisation)

Na movement stimulates further Na recruitment until all channels are open and there is maximum influx of Na.

Once 35mv is reached the Na channels inactivate via closure of the H gate and K channels open.

K influx causes repolarisation.

Question 19

What is the purpose of the refractory period?

Answer 19

Ensures unidirectional movement of Ap’s

So that another potential cannot be generated until the previous one has been sent.

Question 20

What factors increase the speed of propagation in an axon?

Answer 20

The diameter (larger the diameter the faster the conduction)

The degree of myelination

Question 21

What create myelin and lay it down around axons?

Answer 21

Schwaan cells

Question 22

What do myelinated axons require more of? (as opposed to non-myelinated axons)

Answer 22

Energy

Question 23

What are the functions of myelin surrounding axons?

Answer 23

Increase speed of conduction of the AP

Prevent leakage of the current.

Question 24

What are Nodes of Ranvier and what is there function?

Answer 24

Small gaps in myelinated axons

They allow the axon membrane to be exposed to the extracellular fluid which allows exchange of ions to occur

Question 25

Do myelinated or non-myelinated axons have more ion channels and Why?

Answer 25

Myelinated axons have more ion channels (channels concentrated at Nodes of Ranvier)

More ion channels required to generate a stronger potential that can jump across the intervals (nodes of ranvier)

• this is called saltatory conduction