Action potentials

Question 1

What is the normal range of membrane potentials for nerve cells (intracellular recording)?

Answer 1

-40 mV - -80mV

Question 2

What are the rough concentrations of Na+ and K+ inside and outside of the cell?

Answer 2

Inside Outside
K+ = 150mM 5mM
Na+ = 15m 150mM

Question 3

How is the resting potential maintained?

Answer 3

• Na/K pump
• Resting membrane is selectively permeable to K+ which diffuses outside taking the positive charge with it
• Negative inside drags K+ back inside the cell causing the system to be in equilibrium

Question 4

Give an equation for the electro-chemical gradient of a neuron at equilibrium

Answer 4

E(mV) = 58/z log ([X+] outside/[X+] inside)

at 20C where z = valency

Question 5

What is the typical equilibrium potential of: a) K+ b) Na+ c) Ca2+ d) Cl- e) resting potential

Answer 5

a) -80mV
b) +40mV
c) +120mV
d) -75 -> -40 mV
e) -65mV

Question 6

Give the Goldman equation, what does it consider?

Answer 6

E (mV) = 58 log (([K+]o + alpha[Na+]o)/([K+]i + alpha[Na+]i)

Only considers Na+ and K+, where alpha = relative permeability of Na:K

Question 7

When do Na+ and K+ voltage gated channels open?

Answer 7

If a stimulus makes the inside of a cell more positive, shut shortly after even if the inside of the cell is still +ve

Question 8

Which of the voltage gated channels is slower to close?

Answer 8

K channels, however shut if the inside becomes -ve

Question 9

What effect does a larger stimulus have?

Answer 9

• Larger stimulus opens more Nav channels causing gNA> leak

- Autoclose of Nav channels causing Kv channels to open where gK&raquo_space; leak

Question 10

What are the absolute and relative refractory periods?

Answer 10

absolute - 1-2ms immediately after it is impossible to generate another spike
relative - 2-10ms spikes are hard to generate and so a larger stimulus is needed

Question 11

What do the following poisons effect:

a) TTX
b) TEA+
c) Ocubain

Answer 11

a) blocks voltage-dependent Na+ channels
b) blocks voltage-dependent K+ channels
c) blocks Na+/K+ pump

Question 12

How does an AP spread across an axon?

Answer 12

• • charge spreads out form spike stimulating the next region
• velocity of 0.1-10ms depending on diameter
• saltatory conduction if myelinated

Question 13

What are the disadvantages of this system of nerve conduction?

Answer 13

• needs time to integrate
• low frequency ceiling
• frequency needs to cover a wide range of signal strengths

Question 14

Describe extracellular recording

Answer 14

• electrode placed outside but near a neuron in order to measure the field potential in the extracellular space outside neurons
• Field generated by flow of current across membranes of nearby neurons
• Only spikes are picked up, no sub-threshold potentials