Why are fewer action potentials recorded at R2 when TTX is applied between R1 and R2?

Descriptive Title
This should be a statement relating to what the assignment is about

Introductory Paragraph
This should provide background information on each neurotoxin (TTX and Lidocaine) and how these affect the functions of neurons. References are required.

Results Interpretation
This should explain how each neurotoxin (TTX and Lidocaine) affects the ability of a neuron to generate and propagate action potentials at the level of the cell membrane and ion channels.

You must refer to Figures 2-4 and Table 1 to guide your explanation using specific data points as evidence for your discussion (copy and paste these figures into your assignment if you wish). References are not required.

Questions
References are required.

1. What does TTX do to voltage-gated Na+ channels?

2. What does Lidocaine do to voltage-gated Na+ channels?

3. How does the effect of lidocaine differ from the effect of TTX?

4. Why are fewer action potentials recorded at R2 when TTX is applied between R1 and R2?

5. Why are fewer action potentials recorded at R2 when lidocaine is applied between R1 and R2?

6. Pain-sensitive neurons (called nociceptors) conduct action potentials from the skin or teeth to sites in the brain involved in pain perception. Where should a dentist inject the lidocaine to block pain perception?

Conclusion
This should provide an overall summary outlining the importance/application of TTX and Lidocaine to the medical professions. References are required.

References
• A minimum of five references should be provided
• These need to be in APA format (in-text and end-text)
• Do not reference Wikipedia (only .gov, .edu, .org websites are acceptable)

Formatting 11 or 12 size font; double spaced; Word document

Word Count Two pages

– Clinical Case Study –

This assignment will demonstrate your knowledge and understanding of the nervous system, how neurotoxins can affect nerve stimulus propagation, and how these effects can be used for clinical applications.

To prepare for this assignment, please read the following in your textbook:

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Pay particular attention to the following sections:

Basic Principles of Electricity
The Resting Membrane Potential
Membrane Potentials that Act as Signals

Neurotoxins and Action Potentials

The action potential is generated when voltage-gated sodium channels open in sufficient numbers. Voltage-gated sodium channels open when the membrane depolarises. Each sodium channel that opens allows Na+ ions to diffuse into the cell down their electrochemical gradient. When enough sodium channels open so that the amount of sodium ions that enters via these voltage-gated channels overcomes the leak of potassium ions (the potassium leak via passive channels establishes and maintains negative resting membrane potential), threshold for the action potential is reached, and an action potential is generated.

In this activity, you will observe what happens when these voltage-gated sodium channels are blocked with chemicals. One such chemical is tetrodotoxin (TTX), which is extremely poisonous. Another such chemical is lidocaine, which is typically used to block pain in dentistry and minor surgery.

To identify the physiological effect of neurotoxins on impulse conduction, a simple experiment was devised (Figure 1) using:

Nerve chamber
Axon
Oscilloscope – used to observe timing of stimuli and voltage changes in the axon
Stimulator – used to set the stimulus voltage and the interval between stimuli and to deliver pulses that depolarise the axon
Stimulation wires (S)
Recording electrodes (R1 and R2) – used to record voltage changes in the axon
Tetrodotoxin (TTX)
Lidocaine

Figure 1: Experimental Set-Up for Testing the Effects of Neurotoxins

(Zao, P., Stabler, T., Smith, L., Lokuta, A., and Griff, E. (2013). PhysioEx9.1: Laboratory Simulations in Physiology. San Francisco: Pearson.)

Note that the voltage is set to 30mV, the duration is set to 0.5ms, and the interval between stimuli is set to 2.0ms. Multiple stimuli are delivered giving the results above.

The experiment is repeated with the addition of neurotoxins:

TTX is applied to the axon between R1 and R2
Lidocaine is applied to the axon between R1 and R2

These data are presented below.

Experimental Data

Figure 2: Control Data(Normal Neuron Stimulus) Figure 3: Tetrodotoxin Data(TTX Neuron Stimulus)
Figure 4: Lidocaine Data(Lidocaine Neuron Stimulus)

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