Biological Sciences 300/301, Smith College | Neurophysiology

Checklist for Lab 4: Action Potentials in
Earthworm Giant Axons

http://www.science.smith.edu/departments/NeuroSci/courses/bio330/labs/labcheck4.html

UPDATED: February 25, 2016.

1.
Background
for this lab

From the Web instructions for Lab 4, review:

  • The role of giant axons in invertebrates. Look at the cross section of an annelid worm's nerve cord to see the three giant axons in the cord, two lateral and one median.
  • Extracellular recording of action potentials, which appear as much smaller signals than intracellular recordings.
  • The controls for the SD9 stimulators.
  • The video showing the dissection and experimental procedures.

2. Procedures

A. Briefly check the controls of the stimulator, and then remove the extra cable.

B. Anesthetize an earthworm in dilute alcohol. See the Web pages for precautions about this method.

C. Pin out the worm and make an incision to reveal the nerve cord. See the video for guidance.

D. Put the suction electrode in place.

E. Attempt to elicit spikes in the giants mechanically, by stroking or gently prodding the worm. (Don't linger on this step.)

F. Electrically stimulate the nerve cord through pin electrodes at one end of the worm.

(1) Capture a good screenshot of an action potential.
(2) Measure the conduction velocity.
(3) Measure and plot a strength-duration curve using the graph paper on the back of this handout.
(4) Capture one or more screenshots demonstrating the refractory period.

3.
Plotting
data

At the end of the lab, post a single summary page that you make in Pages or Word, with all authors' names on it, showing:

  • a screenshot of an evoked action potential from part (1),
  • the conduction velocity you calculated in part (2),
  • a screenshot of several superimposed traces showing the refractory period (part 4).

Also post the strength-duration graph you plotted in part (3), with all authors' names.

4.
Clean up

Rinse and dry your tools and dissecting dish. Turn off power to all equipment, including the stimulator and the DAM-50 preamplifier.


Strength-Duration Graph