While transmembrane potentials will not be discussed in lecture, an understanding of their causes and consequences will be expected throughout this semester.  You should immediately review your notes from BSCI 230 or equivalent course (a prerequisite for this course!) and then consider the following questions.  Of course the Nervous System Part I section of the required CD will be helpful.  For further detailed reviews of these principles, you may use the NEUROSYS simulation program found on the recitation room computers.  The instructions and suggested exercises are on our Web site.  Your TA can help you if you experience difficulties.

1. Consider sodium, calcium, potassium, and chloride ions.  How are they
    distributed across the plasma membrane of a typical mammalian cell?
    How large and in what directions (In ---> Out or Out ---> In) are their
    concentration gradients?

2. Use the Nernst equation to calculate the equilibrium potentials of each of
    the following ions at 37^oC:
 
 

	ION	[ION]inside	[ION]outside
a.	Na+	10 mM	100 mM
b.	K+	120	12 mM
c.	Ca++	1.3 µM	13 mM
d.	Cl-	4 mM	40 mM

If this were a real mammalian cell, the equilibrium potential for which ion would
most closely approximate V_m ?  Why (explain!)?

3. Refer to the ions above in #2.

    a. List three changes in permeabilities (not concentrations!) that would result
        in depolarization.

    b. List three changes in permeabilities (not concentrations!) that would result
        in hyperpolarization.

    c. List three changes in concentration  that would result in hyperpolarization.
 

    d. List three changes in concentration  that would result in depolarization.
 

4.
    a. Explain completely the ionic events responsible for an action potential in an
        excitable cell (nerve or muscle).
 

    b. Define voltage-gated sodium channel, channel inactivation, refractory period,
        conductance, graded potentials, and conduction velocity.
 
 

5.
    #1. Dr. Harley Schmedlap, noted physiologist and hero to all 440 students, has discovered yet another interesting little beast while wandering through the Bio-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.
 
 

Ion	[Ion]in	[Ion]out	EIon	Rel. Perm.
G+	200 mM	20 mM	________	10
P++	1	100	________	0
C-	10	__________	-61.5 mV	0.1
R+	4	400	________	0.03

     

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 the equation that would accurately predict the membrane potential
     (Vm) for these neurons.
 
 
 

6. Finally, you are may wish to enter the Neurosys program and modify the
    membrane properties of the neuron to make it spontaneously active, i.e.,
    a pacemaker.  (See complete instructions in item #2 under the Membrane
    Characteristics section of the Neurosys program (description on this Web site).