The document summarizes experiments conducted on a frog sciatic nerve to study the effects of various stimuli on nerve transmission and action potentials. In the first experiment, electrical stimulation was applied and it was found that a voltage of 3.0V was needed to trigger an action potential. Chemicals like NaCl and HCl also triggered action potentials when added to the nerve. Ether and curare inhibited nerve transmission, with ether preventing action potentials and curare blocking transmission at synaptic endings. The experiments demonstrated various agents that can induce or prevent nerve impulses and action potentials.

1. Megan Cody
10/23/12
Professor Mirshams
Biol 2401. PL2
Neurophysiology of Nerve Impulses
Introduction
In this report, it’s discussing the effects of various agents on nerve transmission and what kinds
of stimuli trigger an action potential. A nerve cell usually is polarized due to an unequal
distribution of ions on either side of its membrane. When such a polarized membrane is
stimulated at or above its threshold intensity, a wave of action potentials is triggered to move
in all directions away from the site of stimulation. This wave constitutes a nerve impulse, and if
it reaches a muscle, the muscle may respond by contracting (Marieb, 125). In this experiment a
segment of a nerve has been dissected and suspended over a series of metal bars that act as
electrodes. The two electrodes at the bottom are stimulating electrodes and are connected to
an electrical stimulator. The stimulator can be used to apply electrical current to the nerve at
different voltages and frequencies to try to elicit an action potential. The other set of electrodes
are called recording electrodes, and they are connected to an oscilloscope. Differences in
charge between the two recording electrodes cause the line traced on the oscilloscope screen

2. to deflect. Thus, we can observe any action potentials forming in the nerve.(Marieb 130-
131)From the information gathered from the experiment I predict that high voltage will trigger
an Action Potential and all the agents will generate some kind of response on the nerve.
Materials
Electric Stimulation:
Nerve
NaCl
HCI
Oscilloscope
Red Electrical Leads
Black Electrical Leads
Nerve Chamber
Stimulator
Inhibiting a Nerve (computer generated)
Nerve
Curare

3. Ether
Oscilloscope
Red Electrical Leads
Black Electrical Leads
Nerve Chamber
Stimulator
Methods
In the Electrical Stimulation lab we first set the Voltage on the Oscilloscope to 1.0V then clicked
on stimulus button to see the response. If there was no response, the voltage was increased
until action potential was reached. The voltage was then increased by .5V until there was
further peak of the action potential trace.
In the chemical Stimulation lab put a couple drops of NaCl on the nerve to see if it would
generate an action potential. The Voltage was then changed back to 3.0V to see if the new
tracing differed from the original threshold tracing. The nerve was then cleaned. A couple drops
of HCI were added to the newly cleaned nerve to see if it would generate an action potential.
In testing the effects of ether experiment, a couple drops of ether were added to the nerve. The
voltage was then set to 3.0V and the trace was observed. The time on the oscilloscope was then
changed from msec to min and the Interval between Stimuli was changed to 2 mins. The time it
took for the action potential to return to normal was then observed.

4. In the testing the effects of curare, a couple drops of curare were dropped onto a clean nerve
between the stimulator and electrodes. The voltage on the stimulator was then set to 3.0V.
Then the stimulus was tested to see if it would have an action potential.
Results and Discussion
Voltage Glass Bar NaCl HCI Action Potential
3.0V - - - Yes
5.5V - - - Yes
Figure 1.1 Comparison of first reaching Action potential and maxing out on action potential.
Voltage Glass Bar NaCl HCI Action Potential
3.0V - - Yes Yes
3.0V - Yes - Yes
Figure 1.4NaCl versus original action potential.
Voltage Ether Curare Lidocaine Action Potential
3.0V Present Absent Absent No
3.0V Absent Present Absent Yes
Figure 1.5Ether and Curare versus original Action Potential

5. Graph 1.1 Increasing voltage and maxing out of Action Potential
The experiments went as expected with no unusual events that would have introduced error. In
the experiments a sciatic nerve from a frog was used. The leads that were placed o there for
from the stimulator output to the nerve chamber and also to the oscilloscope. The current that
it produces then travels to the nerve. The nerve depolarizes and the electrical current that it
develops continues to loop through the leads. So starting out the experiment the voltage was
set to 1.0V to see if an action potential happened and it didn’t. So by slowly increasing the
voltage it was found that at 3.0V was when the action potential could be first reached as shown
in fig 1.1. Once the action potential was reached an increase of .5V was done to observe the
difference in the action potential. When increased there is a slight increase in the height of the
action potential peak because at the threshold voltage, the smaller fibers in a nerve are
stimulated and an action potential is seen as in Graph 1.1. Increasing the voltage will cause

6. most, if not all of the neural fibers to undergodepolarization. A given nerve is made up of
literally thousands of neuron processes(axons) so this slight increase is noted when all fibers in
the nerve fire (willison 5). Another part of the experiment was chemical stimulation. NaCl and
HCI were added to the nerve to observe the action potential it might produce. Both the HCI and
the NaCl produced action potential as seen in fig 1.4. Another experiment was also done to test
the effect of ether on the sciatic nerve. When a couple of drops were placed on the nerve and
was stimulated no action potential was noticed. No action potential was made because the
ether ananesthetized the nerve which shut down all neuron to neuron communication
(Britannicca 2) as in fig 1.5. The last experiment performed was curare on the nerve. Curare is a
plant in South America typically used to cause paralysis in prey (Marieb 131). A couple drops
were placed on the nerve then stimulated to see if an action potential is formed. No action
potential was formed because nerve propagation is unaffected because curare works on the
synaptic ends of the nerve as in fig 1.5. From the effect of the curare on the nerve it’s clear to
say that Curare would ultimately kill an organism by blocking nerve transmission. It’s clear to
say that all electrical and most chemical stimulation are capable of generating an action
potential in the nerves.
Conclusion
In the labs performed we discover some of the stimuli that caused action potential and effects
of various agents on nerve transmissions. Everything worked the way it was supposed to. We
learned of some agents that prevent the neuron to neuron communication and which

7. ultimately didn’t cause any action potential. In future experiments more agents could be used
to manipulate the nerves a little more and see the reaction of the action potential.

8. References
Marieb, Elaine N., and Susan J. Mitchell. "Neurophysiology of Nerve Impules: Computer
Stimulatiom." Human Anantomy& Physiology.N.p.: n.p., n.d. 125-33. Print.
"Nerve impulse".Encyclopædia Britannica. Encyclopædia Britannica Online.
Encyclopædia Britannica Inc., 2012. Web. 23 Oct. 2012
<http://www.britannica.com/EBchecked/topic/409616/nerve-impulse>.
Willison, Anna. "What Is an Action Potential? (Nerve Impulse)." What Is an Action Potential?
(Nerve Impulse). AAMRICIRE, 12 Nov. 2010. Web. 23 Oct. 2012. <http://antranik.org/what-is-
an-action-potential-nerve-impulse/>.