Just something to think about while on the beach or in Europe.
 
 

#1.    Consider the following measurements taken from an unusual organism (body temperature = 37oC) that inhabits the strange world of Dr. Know-It-All.
 
 

a.   Use the Nernst Equation to give a good approximation of Vm:

      (Don't forget the sign!)
 
 

                                                                                                            __________________mV

b.   Is the actual Vm more + or - than your answer in part a above? Why?
 
 

      ______________________________________________________________________
 
 

c.   If the Vm of the above cell were set by an experimenter to = -50 mV, indicate whether the above ions would then move Faster or Slower than they do at the original Vm:

d.   What is the equilibrium potential for the following ions? Don't forget the sign, please.
   

e.   List 3 changes in ion CONCENTRATIONS that would cause depolarization of the cells:
 
 

f. Now use the Goldman Equation to determine the Vm:
 
 

                                                                                                __________________mV
 
 
#2. It seems the good Dr. K-I-A requires proof of your mastery of the concepts involved in membrane potentials. Therefore we must ask you to answer the following with the data obtained from human neurons ata normal resting potential of - 55 mV.
 

a.         First, fill in the blanks above for the equilibrium potential.
 
 

b.         Give an approximationof the membrane potential (Vm) with the correct sign:

                                                                              ___________________mV

c.         Based on the resting potential of - 55 mV, what may you infer about the permeability of Na⁺ when V_m is at the resting level (= -55 mV)?
   
 
 
   

d.         Draw a representation of an action potential from this cell on the graph BELOW. Use the [ION] data above and other facts you know about changes in V_m during an action potential over time in a typical neuron.
 
 

1e.       What is the peak value of V_m   during an action potential?                  _____________mV
 
 

1f.        What is the maximum (most negative) value for the after potential hyperpolarization (an action potential)?

______________mV

1g.      Using the data from your graph,

            how long are the voltage gated Na⁺ channels open?                      _____________msec
 
 
 
 

#3. Dr. Harley Schmedlap, noted cell biologist and hero to all 230 students, has discovered yet another interesting little beast while wandering through the Zoo-Psych Building. He has taken the following measurements from the beast's nerve cells and surrounding interstitial fluids. He has asked you, his trusty lab partner, to complete his study before sending the results to the Journal of Irreproducible Results.
 

A.        Please supply the missing data by placing the requested values (and signs where appropriate) in the blanks in the table above.
 
 

B.        Please utilize the Nernst equation to give an approximation of the Vm.

            Don't forget the sign!
 
 

                                                                                                __________________mV
 
 

C.        If during an action potential, the Relative Permeability of the nerve membrane to P++ increases to a value of 400, what value will the membrane potential approach?

            (Don't forget the sign!)
 
 

                                                                                                __________________mV
 
 

D.        If only G+ and C- were permeable, would you observe a net movement or diffusion of C- across the membrane? Why or why not?
 

 
 
 
 

E.         List two changes in membrane permeability that would result in an EPSP at the dendrites of the nerves and then two that would yield an IPSP:
 
 

           EPSP:                                                             IPSP:
 
            1.                                                                     1.
 

            2.                                                                     2.
 
 

F.         If Schmedlap observes that these axons are unmyelinated and small in diameter, what could you infer about the conduction velocity of these axons? Explain!
 
 
 
 
 
 
 
 

G.        Please write and solve the equation that would accurately predict the membrane potential (Vm) for these neurons.