Question

please write thorough answers thanks

PART 1 Answer ONLY ONE of the following TWO questions of Part 1 ie a) OR b) a) A typical, healthy nerve cell in the body has intracellular and extracellular Na, K and Cl' concentrations as shown below. Na concentration: Extracellular: = 150 mm K concentration: Extracellular: = 4 mm Ci concentration: Extracellular: = 100 mm Temperature = 37°C (303.3K) R (the Universal Gas constant) = 8.315 VCmol'k F (Faraday's constant) = 96,485 Cmol Intracellular: = 15 mm Intracellular: = 150 mm Intracellular: = 10 mm 1) Describe how the cell establishes and maintains the ion concentration gradients for K and Na* and the membrane transporter involved. (2 marks) ii) If the nerve cell is at rest at 37°C and only has K-selective ion channels open, what will its membrane potential be? (show all working and units) (3 marks) iii) The equilibrium potential for chloride in this cell is -62 mV. If some Cl' channels in the cell now open, in which direction will CI move? Give a brief reason for your answer. (3 marks) iv) Assuming that the populations of K and Cr channels both remain open, will the membrane potential be more positive or negative than -62 mv? Give a brief reason for your answer. (2 marks) OR Part 1 b) i) Draw a graph of an action potential as recorded from a typical nerve axon. Carefully label the units and values on the X and Y axis. (4 marks) ii) Describe the contribution of the voltage-gated Na and K channels to the depolarisation and repolarisation phases of the action potential. Include in your answer how the different timing (kinetics) of the channel gates contribute. (3 marks) iii) Describe how this action potential travels down this unmyelinated nerve axon using a combination of passive and active current flows. (3 marks)

Answer 1

Ai)cell established the sodium potassium concentration gradient by the involvement of NA+-K+ ATPASE which moves 3 sodium outside the cells and 2 potassium ions inside the cells.

iii) as chloride ions has the equilibrium potential of about - 62 mv and presently the potential of the cells is - 96.81 mv .

So if the chloride channels becomes opened , it will try to set is equilibrium potential like -62 mv.

Thus, if chloride channels opens , chloride ions will move outside to make the inner side positive as it is more negative than chloride ions's equilibrium potential.

iv) if both. Cl- and k+ opens then the membrane potential will be in between their equilibrium potential which is -62 and - 96.81.

So the potential will be more less than -62 but more than 96.81 mv Which means it will be more negative inside .

Thank you