Appendix I

Thornton Type 474 Nerve Chamber

Introduction

The type 474 nerve chamber is designed to maintain a nerve in a moist atmosphere for studying compound action potentials in vitro. A set of eight electrodes allows electrical stimulation and recording at fixed points along the nerve.

Operation

Begin by making sure that the nerve chamber is free from dust or dried salt from previous use. If necessary, flush the chamber with warm running water. Residue on the electrode pins can be scraped off with forceps or any convenient tool. Fill the nerve chamber with Pantins or Ringer's solution to a depth where the electrodes are submerged. Allow the electrodes to remain about 15 minutes in the solution. Soaking the electrodes prior to use helps reduce the electrical polarization voltage and drift which may hinder the recording of nerve action potentials. Pour out most of the Ringer's solution from the chamber leaving about 0.5 cm in depth. Be sure that the solution does not contact the electrodes. The chamber is now ready for a nerve.

Grasp the nerve at one end with forceps and transfer it to the nerve chamber. Position the nerve straight across the electrodes spanning as many electrodes as possible for the given length of the nerve. Avoid having the nerve droop over an end electrode and touch the pool of Ringer's solution. This can cause a hum pick-up problem which hinders the recording of action potentials. Cover the nerve chamber with a microscope slide. It is important that the chamber be covered to keep the nerve moist and functional. Although action potentials can be recorded from an open chamber, air currents will cause the baseline of the recording to wander. Moisten the nerve with Ringer's solution during the experiment if exposure to the outside air has caused drying of the nerve.

Connections

Figure 1 illustrates the electrical connections to the chamber for recording action potentials. There are three groups of connections made to the nerve chamber. recording, stimulating and ground. The recording terminals (+, -,G) connect by means of the three black tip splice adapters. Connection to the stimulator is made using the gray two-wire cable. The tip jacks at one end of the cable slide over the two nerve chamber electrode pins intended for stimulation. Finally, the metal base of the nerve chamber is connected to the stimulator electrical ground by using a banana patch cord plugged into the binding post. The connections described correspond to the Thornton equipment. There may be slight differences in terminals leading from the nerve chamber to non Thornton equipment if substituted

Specifications

• Chamber
  • Molded Gray ABS Plastic
• Interior dimensions
  • 3" long x 0.9" wide x 0.85" deep.
• Electrodes
  • Eight 0.080" dia nickel-chromium alloy pins, fixed in position,
  • five electrodes spaced on 1 cm centers. three electrodes spaced on 0.5 cm centers.
• Top Cover
  • A Standard 1" x 3" plastic microscope slide fits over the top of the chamber.
• Electrical Terminals
  • A 5 way binding post allows the metallic base to be connected to an electrical ground to reduce 60Hz hum pick-up.
• Base
  • Black anodized aluminum

From Thornton publication 3033.1m 6/81

Walter I. Hatch
wihatch@smcm.edu

August 12, 2012