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judithlouis judithlouis
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Posts: 37
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12 years ago
Eliciting a Nerve Impulse
Activity 1:  Electrical Stimulation

1.   Do you see any kind of response on the oscilloscope screen?
No, I don’t see any kind of response.
At a voltage 1.0, the oscilloscope screen displays a flat line therefore, there is no action potential.
2.   What was the threshold voltage, or the voltage at which you first saw an action potential?       V
I first saw an action potential at 3.0 voltages.
3.   How does this tracing compare to the one that was generated at the threshold voltage?
When I increase the voltage by 0.5 V; I observed approximately the same graph. However there is a slight increase in the height of the action potential peak. On the other word when I stimulate the membrane with a slight increase in voltage this results in a slight increase in action potential.
4.   What reason can you give for the change?
When you electrically stimulate a nerve at a given voltage, it seems like, not all the nerves were stimulated. The stimulus may result in the depolarization of most of the neurons. However, a higher stimulus voltage was necessary to achieve the depolarization. That is the reason when I increased the voltage by 0.5 voltage, I observed the slight increase in the height.
5.   Record this maximal voltage here:        V
The maximum voltage is 5.0.

Activity 2:  Mechanical Stimulation

1.   When the glass rod is touching the nerve, what do you see on the oscilloscope screen?
When the glass rod is touching the nerve, there is an action potential the oscilloscope screen show a graph with a peak.
2.   How does this tracing compare with the other tracings you have generated?
No difference, this tracing looks like the same to the tracing generated at the threshold voltage.

Activity 3:  Thermal Stimulation

1.   What happens when the heated rod touches the nerve?
When the heated rod touches the nerve an action potential is generated.
2.   How does this trace compare to the trace that was generated with the unheated glass bar?
I observed the same graph but there is a slight increase in the height at the peak of the action potential than the peak generated by the unheated.
3.   What explanation can you provide for this?
Thermal stimulation can induce a nerve response. The heat provokes a stimulation of more neurons than the unheated rod.

Activity 4:  Chemical Stimulation

1.   Does the sodium chloride generate an action potential?
Yes, dropping of sodium chloride over the nerve on the chamber generates an action potential.
2.   Does this tracing differ from the original threshold stimulus tracing?  If so, how?
There is no difference between the threshold voltage setting from activity 1 and the chemical stimulation activity. There are the same.
3.   Does the hydrochloric acid generate an action potential?
Yes, the hydrochloric acid generates an action potential.
4.   Does this tracing differ from the original threshold stimulus tracing?  If so, how?
No, the tracing does not differ from the original threshold stimulus tracing.
5.   To summarize your experimental results, what kinds of stimuli can elicit an action potential?
Nerves can be stimulated by electrical, chemical, thermal, and mechanical stimulation.


Inhibiting a Nerve Impulse
Activity 5:  Testing the Effects of Ether

1.   What sort of trace do you see?
When I stimulate using the voltage 1; 1.5; 2: there is no action potential. The oscilloscope displays a flat line.
2.   What has happened to the nerve?
Numerous physical factors and chemical agents can unpair the ability of nerve fibers to function. For example: deep pressure and cold temperature. Local anesthetics alcohol and numerous other chemicals are also very effective in blocking nerve transmission. In this case, the nerve has been blocked or anesthetized by the ether.
3.   How long does it take for the nerve to return to normal?
      It takes approximately 2 minutes.

Activity 6:  Testing the Effects of Curare

1.   Does this generate an action potential?
No, this does not generate an action potential.
2.   What explains this effect?
 Curane blocks synaptic transmission by preventing neural impulse t flow from neuron to neuron. Therefore, nerve propagation is unaffected, no action potential.
3.   What do you think would be the overall effect of Curare on the organism?
Curane acts by preventing the acetylcholine from acting by blocking synaptic transmission. Curane would paralyze the organism or kill it.

Activity 7:  Testing the Effects of Lidocaine

1.   Does this generate a trace?
No, it does not generate a trace.
2.   What sort of tracing is seen at the threshold voltage?
A flat line is seen at the threshold voltage.
3.   Why does Lidocaine have this effect on nerve fiber transmission?
Lidocaine is a sodium-channel antagonist that prevents sodium channels from opening.  The sodium potassium pump in the membrane maintains the difference in electrical charged established by diffusion of ions therefore, the major action in the extra cellular fluid outside of the cell is the sodium. When a neuron is activated by a stimulus of sufficient intensity, the membrane at this trigger zone, typically the axon hillock briefly becomes more permeable to sodium ion. Lidocaine antagonizes the opening of sodium channels therefore, no action potential possible.

Nerve Conduction Velocity
Activity 8:  Measuring Nerve Conduction Velocity

1.   Which nerve in the group has the slowest conduction velocity?
The earthworm nerve is the group that has the slowest conduction velocity.
2.   What was the speed of the nerve?
The speed of the nerve was 8.60mn/ sec.
3.   Which nerve of the four has the fastest conduction velocity?
The rat nerve 2 has the fastest conduction velocity.
4.   What was the speed of the nerve?
The speed of the nerve was 46.74mn/sec.
5.   What is the relationship between nerve size and conduction velocity?  What are the physiological reasons for this relationship?
The larger the nerve, the quicker the conduction velocity. The conduction velocity depends on the size or diameter of the axon. The diameter of the axon and the presence or absence of a myelin sheath are the most important factors that determine the speed of nerve impulse conduction. Axon with large diameters conduct impulses faster than those with small diameters.
6.   Based on the results, what is your conclusion regarding the effects of myelination on conduction velocity?  What are the physiological reasons for your conclusion?
Myelinated axons conduct impulses faster than do unmyelinated axons. Axons with the largest diameters are all myelinated and therefore capable of saltarory conduction.  The smallest diameter axons are unmyelinated, so their conduction is continuous.
7.   What are the evolutionary advantages achieved by the myelination of neurons?
The myelinaiton of neurons conduct impulse at a higher speed. It allows the voltage –gate sodium and potassium channel flows through the interstial fluid. A nerve impulse leaps from one node of Ranvier to the next along a myelinated axon.
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judithlouis Author
wrote...
12 years ago
please can someone help me with physioex8.0 exerrcise 4

Thank you
wrote...
Valued Member
Educator
12 years ago
please can someone help me with physioex8.0 exerrcise 4

Thank you

Sure, what question? By the way, thanks for providing this resource.
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