Neuron Conduction Velocity

Read the introduction. Then click on each neuron type. Calculate the conduction velocity which is the distance between the 2 electrodes divided by time

Introduction

Nerve Chamber

A common lab in physiology class is to isolate the sciatic nerve of a frog and calculate the conduction velocity. To do this, the sciatic nerve is removed from a pithed frog and placed in chamber much like the one to the right. On one end are electrodes that stimulate the action potential of the nerve. On the other end are electrodes that record action potential passing that point of the nerve.

Sample Readout

Velocity is the distance traveled divided by time. Say a car were to drive 80 miles in one hour. To find its velocity, you divide distance, 80 miles, by time, one hour, to get the velocity of 80 miles per hour. We can therefore calculate the velocity of nerve by measuring the distance between the 2 sets of electrodes, which is 43 mM for our experiment, and dividing it by the time it takes the action potential to appear on the oscilloscope. If you look at the reading to the left, it took 5 milliseconds for the action potential to start. Therefore to find the conduction velocity, you divide 43 mM by 5 mS and get a conduction velocity of 8.6 mM/mS.

Since a perfectly good frog has to be sacrificed to perform this experiment, we are going to be doing a computer simulation instead. On the left hand side are 4 neurons to be simulated. We will be looking at the effect increasing size has on neurons and the difference that myelination makes. Click on each tab and observe the action potential. Then calculate the conduction velocity by dividing 43 mM by the time it took the action potential to start. Your teacher may also have you measure the depolarization, repolarization, and refractor periods.

Small Unmyelinated Neuron

This is a small unmyelinated neuron. It is most likely a type c sensory neuron containing information about pain or temperature to the CNS. Note its resting potential and compare the resting potential to the larger neurons.

nerve conduction for small Unmyelinated

Small Myelinated Neuron

This is a small myelinated neuron. We will pretend this is a type Aδ sensory neuron. It contains information about touch to the central nervous system. Compare its speed as well as its resting potential to the small unmyelinated type C neuron.

nerve conduction for small myelinated

Medium Myelinated Neuron

This is a medium myelinated sensory neuron. We will pretend it is a type Aβ sensory neuron which go from muscle spindles to the CNS and the purpose is to report about the stretch of muscle fibers. Has the resting potential changed from the other neurons? Is this harder to stimulate or easier? Also note that the time has changed on the oscilloscope.

Nerve conduction for medium myelinated

Large Myelinated Neuron

This is a large myelinated sensory neuron. It is a class 1α and it is typically found attached to proprioceptors or Golgi tendon organs (stretch reflexes). When finished with the conduction velocity, go back to the other neuron types. Compare the resting potentials and how hard it is to get to threshold.

Nerve conduction for large myelinated