Resting Membrane Potential Part A: Resting Membrane Potential (vm). For this sec

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Resting Membrane Potential
Part A: Resting Membrane Potential (vm). For this section we will assume atypical distribution ofions inside and outside of cells at 37°C as indicated in Table 8.2. TABLE 82 lon concentrations and Equilibrium Potentials la) If a neuron has a vm of.90 mv what specific type(s) of EXTRACELLULAR RUDImln channels must it have in its membrane? If more than one lnomal range type of channel, what would the 150 nM relative ratio be like? (Not real Na' Ms MIormal nanget 115-14S 15 mM 460 mV numbers, but think about it as: a lot, some, a little none 108 nM (normal range 100 10R 10 mM lange 15 b) If a cell has a vm of-70 mv what specific type(s) of channels must it have in its membrane? If more than one type of channel, what would the relative ratio be like? what would happen to the vm ofthe cell at-7o mv ifyou add twice as much K to the extracellular fluid? d Lets look at this K+ ion effect closer. The table above (8.2) lists the standard ion concentrations inside and outside of our generic cell. Given these values, what is the expected Vm for our generic cell? Do the calculation, IAssume the permeability co-efficient for each ion is as follows: PK 1.0;PN... 0.03 Pa, 0.1] What is this P value all about? What are the numbers telling you about channel density? e) ok now repeat your calculation for Vm assuming that the EXTERNAL K+ or Na+ ion concentrations (only one at a time) are as listed in the table below (all other ion concentrations are as listed in Table 8.2). Fill in the table with your answers. et K+ concn Vm et Nat conn Vm And Looking at your data: What happens to Vm as the K+ concentration goes higher? What would this do to neuronal activity? 10 150 g) What happens to Vm if Na+ levels go higher? And to neuronal activity? [Thought Q: Before we get carried away with Na+ ion concentration,1will tell you that Nations play a huge role in extracellular osmolarity. So what might really bappen to the once we go to say 200

Explanation / Answer

1a. If a neuron has a Vm of -90mV, its membrane have K+ and Cl- channels. This condition i.e, hyperpolarization results due to efflux of K+ through K+ channels and influx of Cl- through Cl- channels.

1b. If a cell has a Vm of -70 mV, its membrane have K+ channels.

1c. If twice as much K+ is added to the extracellular fluid, K+ ion will move inside the cell down the concentration gradient resulting in excitibility of cells and causing depolarization i.e, Vm increases to a positive value.

1d. The expected Vm can be calculated by the following equation:

Vm= RT/F ln ( (PK (K+ )O + PNa (Na+)o + P Cl (Cl- )i ) / ( PK (K+ )i  + PNa (Na+)i + P Cl (Cl- )o)

=( (8.314* 310)/ 96485) ln ( (1*5 + 0.03*145 + 0.1*10) / (1*150 + 0.03*15 + 0.1*108) )

= -0.07 V

P value represents the permeability values of different ions. Since at rest PK is larger than PNa and PCl , so permeability values are reported as relative permeabilities with PK.

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