Nerve Cells

Question 1 Part 1

A nerve cell has intracellular and extracellular Na+ and K+ concentration such that the equilibrium potential for Na+ (ENa+) = +60 mV and that for K+ (EK+) = -90 mV. The nerve cell has a measured resting membrane potential of -65 mV.

To which ion is the membrane of this nerve cell more permeable?

Answer: K+. The membrane potential is determined by the ion(s) to which the membrane is permeant.

Question 1 Part 2

If in a nerve cell ENa+ = +60 mV and EK+ = -60 mV, then, if the nerve membrane was permeable only to K+, the resting membrane potential would most likely be:

(a) 60 mV (b) 120 mV (c) 0 mV (d) -60 mV (e) -70 mV

Answer: -60 mV. Since the membrane is permeable only to K+, the resting membrane potential is likely to be the equilibrium potential for K+.

Question 1 Part 3

If in a nerve cell ENa+ = +60 mV and EK+ = -60 mV, then, if the nerve membrane was permeable only to Na+, the resting membrane potential would most likely be:

(a) 60 mV (b) 120 mV (c) 0 mV (d) -60 mV (e) -70 mV

Answer: 60 mV.

Question 2 Part 1

Chamber A contains the following ions at the concentrations: [Na+] = 10 mM, [K+] = 100 mM, [Cl-] = 110 mM.

Chamber B contains the following ions at the concentrations: [Na+] = 100 mM, [K+] = 10 mM, [Cl-] = 110 mM

If the membrane is permeable only to Na+

(a) what is the trans-membrane potential difference?

Answer: The Nernst equation is E = 60 log [x1]/[x2]

If the membrane is permeable only to Na+, and [Na+A] = 10 and [Na+B] = 100 then E = 60 log (10/100) = -60 mV .

(b) which chamber is negatively charged with respect to the other?

Answer: Chamber B is -ve with respect to A.

If the membrane is permeable only to K+

(a) what is the trans-membrane potential difference?

Answer: If the membrane is permeable only to K+, and [K+A] = 100 and [K+B] = 10 then (a) E = 60 log (100/10) = 60 mV

(b) which chamber is negatively charged with respect to the other?

Answer: Chamber A is -ve with respect to B.

Question 2 Part 2

Chamber A contains the following ions at the concentrations: [Na+] = 58 mM, [K+] = 148 mM, [Cl-] = 100 mM, [A-] = 106 mM

Chamber B contains the following ions at the concentrations: [Na+] = 200 mM, [K+] = 2 mM, [Cl-] = 50 mM, [A-] = 152 mM

If the membrane is permeable only to Na+

(a) what is the trans-membrane potential difference?

Answer: If the membrane is permeable only to Na+, and [Na+A] = 58 and [Na+B] = 200 then E = 60 log (58/200) = -32 mV.

(b) which chamber is negatively charged with respect to the other?

Answer: Chamber B is -ve with respect to A.

If the membrane is permeable only to K+

(a) what is the trans-membrane