Neurone excitability

Question 1

When Vm is negative is the inside of the cell more positive or negative than the outside?

Answer 1

Inside of the cell is more negative

Question 2

What does Nernst equation calculate?

Answer 2

How much a given ion contributes to a resting potential

Question 3

Describe the net flow of an ion when Vm = Vnerst for that ion?

Answer 3

No netflow

Question 4

Which ion will pull Vm to its own Vnerst

a) the most ionic
b) the most permeable
c) largest ion
d) smallest ion
e) the least permeable

Answer 4

b

Question 5

Which ions is Vm closest to?

a) Cl
b) K
c) Na

Answer 5

Cl and K

Question 6

Why is Vm close to Pk?

Answer 6

Lots of K+ leaky channels

Question 7

Why does Vm not equal Ek exactly?

Answer 7

Some leakage of Na+ and Cl-

Question 8

Why is Goldman-Hodgkin_Katz constant more accurate that Nernst?

Answer 8

Takes into account all ions and permeabilities

Question 9

What causes a neural signal?

Answer 9

Large changes in ratios of permeabilities for different ions through gated channels

Question 10

Does active or passive propagation cause propagation without decrement?

Answer 10

Active

Question 11

Why can axons with a larger diameter propagate further/

Answer 11

Less resistance

Question 12

What is a graded response?

Answer 12

Bigger stimuli = bigger response

Question 13

What is a summate response?

Answer 13

Multiple stimuli = summed response

Question 14

What is overshoot?

Answer 14

When the membrane potential is above 0mV

Question 15

What gates do Na+ voltage gated channels have?

Answer 15

Internal h gate (inactivation)

External m gate (activation)

Question 16

What gates do K+ voltage gates channels have?

Answer 16

n gate

Question 17

What is the state of the gates in resting conditions?

Answer 17

Most Na+ h gates open but all m gates closed - so the Na+ channels are closed
K+ n gates closed
Neither contribute to Vm

Question 18

In terms of voltage gated ion channel gates what happens during depolarisation?

Answer 18

Na+ m gates open, Na+ moves into the cell
Depolarisation occurs and this causes more m gates to open = positive feedback.
Na+ is very permeable and Vm moves towards ENa

Question 19

Why does Vm never reach ENa during depolarisation?

Answer 19

h gates begin to slowly close, so Vm is just below ENa

Question 20

What is the stage called when h gates are closing?

Answer 20

Absolute refractory period

Question 21

What happens to gates during depolarisation?

Answer 21

n gates slowly open

Question 22

What is the purpose of undershoot?

Answer 22

K+ is higher out of the cell that it is at rest, undershoot allows K+ channels to close and membrane potential to settle

Question 23

What is the purpose of refractory period?

Answer 23

Limits firing frequency

Question 24

During relative refractory period when can an AP occur?

Answer 24

Suprathreshold stimuli

Question 25

What will an AP during relative refractory period look like?

Answer 25

Reduced amplitude as fewer NA+ channels are open

Question 26

Why does an AP always propagate forward?

Answer 26

Refractory period - ahead of the AP Na+ channels are ready to be opened
Behind they are in the inactive state

Question 27

What type of propagation occurs between the nodes of Ranvier?

Answer 27

Passive propagation