Neurophysiology of Nerve Impulses The Action Potential Conduction Velocity

2/9/2021 PhysioEx Exercise 3 Activity 7 PhysioEx Lab Report Exercise 3: Neurophysiology of Nerve Impulses Activity 7: The Action Potential: Conduction Velocity Date: 9 February 2021 Pre-lab Quiz Results You scored 100% by answering 5 out of 5 questions correctly. 1 An action potential can be propagated along an axon because there are _______ channels in the membrane. You correctly answered: voltage-gated. 2 The units of conduction velocity are You correctly answered: meters/second. 3 Which of the following will affect axonal conduction velocity? You correctly answered: both the diameter of the axon and the amount of myelination. 4 Which of the following describes an A fiber? You correctly answered: large diameter, heavily myelinated. 5 Which of the following describes a C fiber? You correctly answered: small diameter, unmyelinated. Experiment Results Predict Questions 1 Predict Question 1: How will the conduction velocity in the B fiber compare with that in the A Fiber? Your answer: The conduction velocity in the B fiber will be slower because the B fiber has a smaller diameter and less myelination. 2 Predict Question 2: How will the conduction velocity in the C fiber compare with that in the B Fiber? i 1/5 2/9/2021 PhysioEx Exercise 3 Activity 7 Your answer: The conduction velocity in the C fiber will be slower because the C fiber has a smaller diameter and less myelination. Stop & Think Questions 1 Note the difference in time between the action potential recorded at R1 and the action potential recorded at R2. The distance between these sets of recording electrodes is 2 centimeters (0.02 m). Convert the time from milliseconds to seconds, enter the time (in seconds). You answered: 0.002 sec. 2 Calculate the conduction velocity in meters/second by dividing the distance between R1 and R2 (0.02 m) by the time it took for the action potential to travel from R1 to R2. Enter the conduction velocity. You answered: 10 m/sec. 3 Note the difference in time between the action potential recorded at R1 and the action potential recorded at R2. Convert the time from milliseconds to seconds, enter the time (in seconds). You answered: 0.01 sec. 4 Calculate the conduction velocity in meters/second by dividing the distance between R1 and R2 (0.02 m) by the time it took for the action potential to travel from R1 to R2. Enter the conduction velocity. You answered: 2 m/sec. 5 Note the difference in time between the action potential recorded at R1 and the action potential recorded at R2. Convert the time from milliseconds to seconds, enter the time (in seconds). You answered: 0.1 sec. 6 Calculate the conduction velocity in meters/second by dividing the distance between R1 and R2 (0.02 m) by the time it took for the action potential to travel from R1 to R2. Enter the conduction velocity. i 2/5 2/9/2021 PhysioEx Exercise 3 Activity 7 You answered: 0.2 m/sec. Experiment Data Axon Type Myelination Stimulus Voltage (mV) Distance From R1 to R2 (m) Time between APs (msec) Time between APs (sec) Conduction Velocity (m/sec) A fiber Heavy 30 0.02 2 0.002 10 B fiber Light 30 0.02 10 0.01 2 C fiber None 30 0.02 100 0.1 0.2 i 3/5 2/9/2021 PhysioEx Exercise 3 Activity 7 Post-lab Quiz Results You scored 100% by answering 4 out of 4 questions correctly. 1 Action potential conduction velocity is fastest in which of the following fibers? You correctly answered: A fibers. 2 Action potential conduction velocity is slowest in which of the following fibers? You correctly answered: C fibers. 3 Why did the timescale have to be changed to measure the conduction velocity of the C fibers? You correctly answered: The total time shown on the oscilloscope would have been too short to observe the action potential at R2. 4 The axons from touch fibers are A fibers, and the axons from pain fibers are C fibers. When you stub your toe, which would you expect to perceive first? You correctly answered: your toe touching something. Review Sheet Results 1 How did the conduction velocity in the B fiber compare with that in the A Fiber? How well did the results compare with your prediction? Your answer: B fibers have a smaller radius and less myelin than A fibers so the velocity is slower than velocity of A fibers as predicted. i 4/5 2/9/2021 PhysioEx Exercise 3 Activity 7 2 How did the conduction velocity in the C fiber compare with that in the B Fiber? How well did the results compare with your prediction? Your answer: The velocity in the C fiber is faster than velocity of B fibers as I predicted. 3 What is the effect of axon diameter on conduction velocity? Your answer: The smaller the axon diameter makes in conduction velocities slower. 4 What is the effect of the amount of myelination on conduction velocity? Your answer: A greater layer or amount of myelination makes a faster conduction velocity. 5 Why did the time between the stimulation and the action potential at R1 differ for each axon? Your answer: Each differed in radius and thickness of myelination. 6 Why did you need to change the timescale on the oscilloscope for each axon? Your answer: When conduction velocity slowed, a longer time needed to record action potential. i 5/5