Membrane permeability

Question 1

What are the two main factors that make a neurone excitable?

Answer 1

Resting membrane potential

Voltage-gated NA+ channels

Question 2

How can you measure the membrane potential experimentally?

Answer 2

With a volt meter

Question 3

How is the membrane selectively permeable?

Answer 3

K+ selective channels are in the lipid membrane which causes the potential difference as only K+ can pass through .

the con. gradient and electrical charge gradient are in opposite directions

Question 4

What is the equation to calculate the equilibrium potential ?

Answer 4

Nernst Equation.

E= RT/ZF x log e( [ ion] out/[ion] in)

R=gas constant
T= temp in Kelvin
z= valency of the ion
f= faraday constant

Question 5

How is the Nernst Equation simplified at 37C ?

Answer 5

EmV= 61.5 Log 10 ( [K]out/[K]in)

Question 6

What is the relationship between Em and [K+]?

Answer 6

Em should be directly proportional to any change in log [K+]out

Question 7

Why does the relationship between Em and log10 [K+]out deviate from linearity?

Answer 7

Neuron has a lower permeability for Na+ leak channels than K+ leak channels.
Em= average weighted between Ek and Ena

Question 8

What is the Goldman constant Field Equation?

Answer 8

Em = 61.5 log PK[K+]o + PNa[Na+]o + PCl[Cl-]i
PK[K+]i + PNa[Na+]i + PCl[Cl-]o

At 37c

Question 9

What is the relationship between Cl- and EM?

Answer 9

Em drives redistribution of Cl- passively

as Ecl more -ve than Em

Question 10

How is membrane potential generated?

Answer 10

3Na+ out the cell
2K+ into the cell

ATP hydrolysed by ATPase transporters

Question 11

What is the permeability ratio for pNA+ and pK+?

Answer 11

pNa/pK+ = 0.01

Question 12

What is Depol

Answer 12

Depol. - Vm approaches ENa. the spike is due to a transient increase in PNa

Question 13

What is repol?

Answer 13

Repol. - Vm approaches EK. the spike is due to a transient increase in PK