Single and multiple-impulse nerve stem compound action potentials were recorded at different temperatures (temperature decreasing from 20°C at temperature interval 2°C) in toad nervus ischiadicus. In the first experiment, we found the max compound action potential deceased from about 8.5mv at 20°C to 0.0 mv at 2°C and action potentials were completely inactivated at 2°C, so we thought that a lower temperature could truly inactivate nerve stem compound action potentials. The results of parameter discrimination using the jumping conduction model showed that the number of nerve stem fibers hindered continuously with temperature declining gradually became more and more and we could see that they fiber was first hindered and the following was B fiber, the reason was that the fiber whose conduction velocity was slow and whose threshold was high was more easily inhibited. The results of the second experiment showed that the max crossing frequency declined from about 175Hz at 20°C to about 30Hz_ at 10°C this showed that the refractory period of the nerve fibers was prolonged with temperature decreasing, and from this we concluded that lower temperatures can truly inactivate sodium pump.
From the above-experimental results and the facts that the sodium and calcium channels gradually inactivate with temperature declining, this paper presented the mechanism of lower temperature analgesia:
1. The proteins of sodium pump denature at lower temperature, thus the sodium pump can not pump the inward sodium back out to the cell membrane and the normal resting potential also can not be kept, the nerve fiber action potentials then inactivate;
2. Sodium channels inactivating at lower temperatures also is one of the reasons why action potentials inactivate;
3. As we know, acetylcholine releasing from nerve ending is very important when excitation transmits from nerve to muscle and acetylcholine releasing needs calcium. However, because the calcium channels inactivate and calcium can not influx at lower temperatures, acetylcholine can not be released at lower calcium concentration and action potentials also can not be transmitted between two nerve units, of course, the sense of pain can not be transmitted;
4. The mobility and permeability of nerve cell membrane decreasing at lower temperatures hinders some normal physical and chemical reactions.
Key Words: Lower Temperature, Compound Action Potential, Calcium and Sodium Channels, Sodium Pump