Why extreme heat makes you feel cold.
Posted 10 November 2003 - 01:42 AM
You actually are feeling cold. The cold receptors that have been heated are losing heat to the nearby cells that are not as hot. Even though the water may not be very warm, if the cold receptors are very warm compared to the cells around it, they can still give enough heat away to make you feel cold in that area.
Posted 10 November 2003 - 07:48 AM
1) It ignores the role of warmth receptors
2) It assumes that a shower of water at any given tempterature could result in cutaneous cells in direct contact with each other being at distinctly different temperatures.
Warmth and cold are mediated by separate populations of thermal receptors, and temperature sensitivity is punctuate, i.e. these receptors innervate areas of the skin (about 1mm dia.) where thermal stimulation elicits the sensation of either warmth or cold (depending on the stimulus > or < 34 degrees C).
Thermal receptors respond to changes in skin temperature, and each (cold and warm) have a preferential range of sensitivity. Cold receceptors respond optimally within a range of 1 degree to 20 degrees below normal skin temp (~34 degrees C). Warmth receptors respond between 32 degrees C and around 45 degrees C.
When you apply a warm or cold stimulus, the appropriate (warm or cold) receptors fire rapidly in response to the sudden change, but if the stimulus is constant, the volleys decrease in frequency (habituation), which is why we go 'OohAhOohAh' when we first get into a hot bath or shower, but without changing the water temp, just go 'Aaaahhh' after a minute or two.
There is another type of thermal receptors (not specific to thermal stimuli) called polymodal receptors. These have a wide dynamic range and respond to heat stimuli (>45 degrees C), noxious cold and mechanical stimuli of sufficient intensity to cause pain. These receptors begin to take over where thermal receptors leave off (at stimulus temps outside their range, thermal receptor activity is reduced).
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