Biomedical Engineering Reference
In-Depth Information
end
Store values of interest to a file
Homework Problems
(1) If a stimulus is above a strength duration curve and the membrane is active, will and action potential
fire? Explain.
(2) The following data were recorded at the peak of a Hodgkin-Huxely action potential:
353
.
574
μA
cm
2
I
K
=
394
.
59
μA
cm
2
I
Na
=−
3
.
36737
mS
cm
2
g
K
=
130
.
7429
mS
cm
2
g
Na
=
m
=
0
.
889
h
0
.
288
E
K
=−
=
75
.
0
mV
E
Na
=
50
mV
.
a) What is the peak magnitude of the action potential in mV?
b) How does this compare to
E
Na
? What does this mean?
c) Compute the fraction of K+ channels open.
d) What is the value of
I
leak
?
(2) In a voltage-clamp experiment, the transmembrane potential (
V
m
) was changed from rest (-60mV)
to 0mV, kept at 0mV for 100ms, and then changed to -50mV. Relevant parameters are given in
the table below (time constants in msec).
Table 3.3:
V
m
α
m
τ
m
α
h
τ
h
-60mV 0.225
0.238
0.0697
8.51
-50mV 0.433
0.368
0.0423
6.16
0mV
3.62
0.266
0.00347
1.05
a) Sketch the holding potential and label the times and voltage levels.
b) Compute the fraction of h gates open at
t
100
msec
.
c) Compute the fraction of h gates that are open at
t
=
104
msec
.
d) Compute the probability of an Na+ channel being open at
t
=
=
104
msec
.
(3) Extend the Hodgkin-Huxely model to include Potassium buffering by an intracellular organelle.
Be sure to write down differential equations for the concentrations of
K
+
in the organelle, cell,
