Neurophysiology of Nerve Impulses Lab

Lab Report Pre-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 Voltage-gated Na+ channels are membrane channels that open You correctly answered: when the membrane depolarizes. 2 When open, Na+ channels allow You correctly answered: Na + ions to diffuse into the cell. 3 Which of the following is true of an action potential? You correctly answered: All of these answers are correct. 4 Which of the following can reduce the likelihood of an action potential? You correctly answered: All of these can reduce the likelihood of an action potential. Experiment Results Predict Questions 1 Predict Question 1: If you apply TTX between recording electrodes R1 and R2, what effect will the TTX have on the action potentials at R1 and R2? Your answer: TTX will block the response at R2 but have no effect at R1. 2 Predict Question 2: If you apply lidocaine between recording electrodes R1 and R2, what effect will the lidocaine have on the action potentials at R1 and R2? Your answer: Lidocaine will block the response at R2 but have no effect at R1. Stop & Think Questions 1 Enter the peak value of the response at R1 and R2. You answered: 100 μV. 2 With a slower timescale, the appearance of the action potentials generated at R1 and R2 will appear to You correctly answered: be compressed in time but have the same peak value of response. 3 Why do you think TTX is not used during dental procedures? You correctly answered: TTX irreversibly blocks voltage-gated sodium channels in axonal membranes. Experiment Data Condition Stimulus Voltage (mV) Electrode Peak Value Peak Value Peak Value Peak Value Peak Value of Response of Response of Response of Response of Response (μV) 2 sec (μV) 4 sec (μV) 6 sec (μV) 8 sec (μV) 10 sec Control 30 R1 100 100 100 100 100 Control 30 R2 100 100 100 100 100 TTX 30 R1 100 100 100 100 100 TTX 30 R2 100 100 0 0 0 Lidocaine 30 R1 100 100 100 100 100 Lidocaine 30 R2 100 100 100 0 0 Post-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 In the control, the amplitudes of the action potentials at R1 and R2 are the same. Which of the following explains this? You correctly answered: All of these are reasonable explanations. 2 Blocking the voltage-gated Na+ channels between R1 and R2 with TTX blocks You correctly answered: the propagation of the action potential from R1 to R2. 3 When voltage-gated Na+ channels between R1 and R2 are blocked with TTX, an action potential is still recorded at R1 because You correctly answered: the voltage-gated Na+ channels between the stimulus and R1 are unaffected by the TTX. You correctly answered: action potentials from sensory neurons in the lips are blocked. Review Sheet Results 1 What does TTX do to voltage-gated Na+ channels? Your answer: Closes the R2 channels, which does not allow Na+ to move into or out of the cell. 2 What does lidocaine do to voltage-gated Na+ channels? How does the effect of lidocaine differ from the effect of TTX? Your answer: Lidocaine blocks the diffusion of sodium through the voltage-gated sodium channels. It is slower at closing the gates. 3 A nerve is a bundle of axons, and some nerves are less sensitive to lidocaine. If a nerve, rather than an axon, had been used in the lidocaine experiment, the responses recorded at R1 and R2 would be the sum of all the action potentials (called a compound action potential). Would the response at R2 after lidocaine application necessarily be zero? Why or why not? Your answer: With a compound action potential, the results would not necessarily be zero because some axons could remain unaffected. 4 Why are fewer action potentials recorded at recording electrodes R2 when TTX is applied between R1 and R2? How well did the results compare with your prediction? Your answer: The voltage-gated Na+ channels between the stimulus and R1 are unaffected by the TTX. 5 Why are fewer action potentials recorded at recording electrodes R2 when lidocaine is applied between R1 and R2? How well did the results compare with your prediction? Your answer: Fewer action potentials are recorded at R2 which means lidocaine blocked the responses at 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? Your answer: Lidocaine should be applied to the receptors to prevent the generation of an action potential that would lead to the perception of pain.