Question 4. You record the electrical activity of a neuron with intracellular el

Question

Question 4. You record the electrical activity of a neuron with intracellular electrodes. The normal resting membrane potential is measured to be -50 mV. When Na" channels are blocked the resting potential is -64 mV. When K' channels are blocked, the resting potential is +29 mV Assume that the membrane is not permeable to any other ions. All measurements are conducted at room temperature. a. (2 pts) What are the equilibrium potentials for Na" and K'? b. (2 pts) What ratio of K' to Na* permeability would account for the neuron's normal resting potential? c. (2 pts) If you suddenly made the cell much more permeable to K', what would happen to neuron's resting potential? Near what value would it stabilize? d. (2 pts) If you were to add KCI to the extracellular solution so that the external K concentration became equal to the intracellular K concentration, what would the cell's resting potential become? (Hint: first determine the new Ex)

Explanation / Answer

Q4 a-

Answer-

The most resting neurons are permeable to Na+ and Cl- as well as K+. Permiability of Na+ in particular, is the main reason why the resting membrane potential is different from the potassium equilibrium potential.

In a resting neuron, Na+ and K+ are permeant and able to cross the membrane. Na+ will always try to drag the membrane for potential toward its (positive) equilibrium potential. K+ will try to drag the membrane potential toward its (negative) equilibrium potential.

Q4 b-

Answer-

Generally one type of ion Na+ ( rather then K+) move across the neron cell membrane. For equilbirium process, when three molecules of Na+ ions enter into the cell then one mol of K+ is efflux form the cell for maintaining equillbirum the neuron cell. ( note- K+ cannot move its self its released by Na+ - K+ ATPase pump with the help of energy). Its help in normal resting potencial.

Q4 c

Answer-

In case K+ gets more permeable in neuronal cells. It means K+ will essily released from cells without require more ATP and it will directly affects the resting potential. At the time of depolarization the cell will gets essily resting phase means it will decrease the depolarization process. And in resting potencial cell may be goes into hyperpolarization state.( Value- More K+ permeability will hyperpolarized the neurons less than -50 mV.)

Q4 d-

Answer-

In addition of KCl in extracellular and it equalized intra and extra cellular K+ concentration.

There will be change in depolarization state. In depolarization cell will need more Na+ entry. In this stage cell need potencial from -70 mV to + 30mV.

(x) = 2.3 log(x) and 2.3 RT/F = 60mV at 30°C, the Nernst equation can be rewritten as

EK=60mVzlogKo/Ki

Thus, the membrane potential is 60mV when the K+concentration inside is 10 times the concentration outside.

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