more about nerve and muscle ion channel function:
Nerve axons come in two varieties: myelinated and unmyelinated. Myelin is a fatty sheath that surrounds the myelinated fibres and allows faster transmission of nerve impulses. Action potentials race along myelinated nerve fibres at rates of up to 100 metres/second or more, but can barely manage 1 metre/second in many unmyelinated fibres. The rate at which action potentials are transmitted also depends on temperature, and conduction slows down when the nerve is cooled. [jl note: or excessively warmed]
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a stereotyped trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and endocrine cells, as well as in some plant cells. In neurons, they play a central role in cell-to-cell communication.
What is the effect of temperature on the shape of the action potential?
Answer: The effect of temperature is mainly on ionic permeability of the neuronal membrane. Specifically, sodium channels open and close faster at higher temperature. Reductions in temperature lengthen the action potential and slow conduction velocity...these are the classic experiments of Hodgkin and Katz (1949).
http://www.ncbi.nlm.nih.gov/pmc/article ... 2-0254.pdf
THE EFFECT OF TEMPERATURE ON THE ELECTRICAL ACTIVITY OF THE GIANT AXON OF THE SQUID (Hodgkin and Katz, 1949)
...effects on action and resting potential in sea water solution at different temperatures...
http://www.ncbi.nlm.nih.gov/pmc/article ... 77/?page=3
(link to results graphs p242)
from summary p249
The action potential diminished in amplitude as the temperature was
raised. This change was slight from 2 to 200 C., the mean value falling from 85 to 80 mV. The decrease in spike height became very rapid above 350 0., and a reversible 'heat block' occurred between 35 and 400 C.
The positive phase of the membrane action potential was diminished at
low and high temperatures and reached a maximum, of approximately
10-15 mV., at about 250 C.
excellent intro/exercises on action potential in nerves:
http://outreach.mcb.harvard.edu/animati ... ential.swf
sodium-potassium pump close-up video, showing ATP activity: