I am puzzled by how the nervious system can determine between hot and cold. Nerves only send back pulses. Heavy sensations result in faster pulsing than lite sensations. (A given pulse is generally the same strength.) This is the only scalar value that a given nerve passes up as far as I know. Thus, how does the body know what is hot and cold?

I do notice that if I stick my hand in and out real *fast* from a glass of hot or cold water, I can tell that the temerature is extreme, but not which way.