Human Physiology: The Action Potential
9/10/2009
Prof. Sungkwon Chung (schung@med.skku.ac.kr)
1. Basic concepts:
After-hyperpolarization (Fig. 5-5), threshold (Fig. 5-1), All-or-none principle
Refractory period (absolute, relative; Fig. 5-9)
Patch-clamp method (Fig. 5-8)/ voltage-clamp
Saltatory conduction (Fig. 5-12)
2. Generation and termination of action potential
-
voltage-dependent K+ and Na+ channels
- Mechanism for the generation of action potential
http://www.sumanasinc.com/webcontent/animations/content/electricalsignaling.html

Which channels are responsible for the generation of action potential?

What is the origin of threshold of action potential?
3. Refractory period determines the frequency coding of stimulation intensity

What is the major factor for the refractory period of action potential?
4. Factors determining the speed of action potential propagation
-
Propagation of action potential: unidirectional vs. bidirectional
http://lessons.harveyproject.org/development/nervous_system/cell_neuro/action_potential/propagation.html
http://msjensen.cehd.umn.edu/1135/Links/Animations/Flash/0014-swf_action_potenti.swf
- Factors determining the velocity of action potential: Saltatory conduction:
http://www.blackwellpublishing.com/matthews/actionp.html
http://wps.prenhall.com/wps/media/objects/1551/1588888/web_tut/07_02/nav/07_02.html

What are the factors determining the speed of action potential propagation?
5. Myelination increase the speed of AP propagation and disease associated with demyelination (Fig.
5-10, 11)
-
Multiple sclerosis (MS) is a chronic, inflammatory, demyelinating disease
http://www.livingpixels.net/ms.html

How myelination increases the speed of AP propagation?

How demyelination affects the speed of AP propagation?
Problems
1. The action potential of a neuron (
).
a) is initiated by efflux of Na+
b) is terminated by efflux of K+
c) is associated with efflux of Ca2+
d) is not associated with any net movement of Na+ or K+ across the cell membrane
2. The information of stimulation strength is coded in the nervous system by (
).
a. Varying the frequency of action potentials
b. Altering the amplitude of action potentials
c. Changing the speed of action potential conduction
d. Changing the type of neurotransmitter released
2. What is the reason for the action potential refractory period? (
a) K+ channel inactivation
b) Na+ channel inactivation
c) K+ channel activation
d) Na+ channel activation
)
4. A drug completely blocks Na+ channels in nerves. Which of the following effects on the action
potential would it be expected to produce?
1) Block the occurrence of action potentials
2) Increase the rate of rise of the upstroke of the action potential
3) Shorten the absolute refractory period
4) Abolish the hyperpolarizing afterpotential
5) Increase the Na+ equilibrium potential.
5.What is the conduction velocity rate of a C-type sensory fiber, which has small diameter (1 m)
and is not myelinated? (
a. 120 m/sec
b. 50 m/sec
)
c. 10 m/sec
d. 2 m/sec
6. Black line in the figure below represents current-voltage relationship of K+ current determining
resting membrane potential (Er), and the yellow line represents that of voltage-dependent Na+
current. The green line represents the sum of two currents. Let’s assume that resting membrane
potential is -80 mV, and positive current is injected.
1) What would happen in membrane potential, if membrane potential reaches -40 mV?
2) What would happen in membrane potential, if membrane potential reaches -10 mV?
7. The following figure shows the membrane potential changes during action potential.
E Na, EK
represent Nernst potentials of Na and K , respectively.
+
+
1) Draw the permeability changes of Na+ and K+ during action potential in the figure.
2) Let’s assume that you had invented a drug “X” which would activate K+ channel, thus
increasing K+ permeability by 100%.
What kind of change do you expect from the shape
of action potential in the presence of “X”?