PCP Set Point

Question 1

What is the hypothesis for the point and the counterpoint?

Answer 1

Point: Core temps are defended at a set point

Counter Point: Core temps are not defended at a set point.

Question 2

What are the 2 main methods of determining whether temp is defended about a set point/null zone? Describe each

Answer 2

1. Direct measures
   - temp is recorded in various experimental conditions
2. Indirect measures
   - neural model is constructed to explain
   physiological response to differing stimuli

Question 3

What evidence did the point find to support their hypothesis?

Answer 3

• During cold immersion, metabolic heat was still being produced while sweat was produced and additional heat was lost from hand. The error bars overlapped indicating that this whole range happens simultaneously. During warm immersion heat loss and heat lost from forearm overlap. Overlap is 0.05oC which is physiologically irrelevant.
  Hammels reciprocal cross inhibition, temperature insensitive cells inhibit warm effectors and stimulate cold effectors, cutaneous thermoreceptors sum in the spinal cord, then project to warm.sensitive neurons in the hypothalamus which stimulate warm effectors and inhibit cold effectors.
  Drugs (Nalbuphine and atropine) lower and higher thresholds for sweating and shivering simultaneously.
  Dehydrated men sweat less for a given temperature.
• Using direct methods, which is varying temperature in experimental conditions, they determined that core temps for thermoregulatory reponses (vasomotor, control, sweating) not to be significantly different suggested its defended at a point, any deviation from this point results in TR responses.
• Indirect: use of neural model. Summation of warm/cold signals in the hypothalamus, would lead to shivering or sweating.

Question 4

What evidence did the cpoint find to support their hypothesis?

Answer 4

• Exp looked at this thru cold and then rest then exercise and found significant difference in onset of shivering and sweating
• Forced warm air
• null zone is defined as the range of temperatures in which no shivering or sweating response is seen, only a proportional vasomotor response
• Experiment done which placed subjects neck deep in temperature controlled water, saw significantly different values in onset of shivering and sweating when measuring rectal and esophageal temperatures → supports evidence of null zone, as the two values would not have been significantly different if set point was the case of thermoregulation
• Study measuring tympanic membrane in men and women showed the two genders to have a 1.4 +/0 0.6 and 1.2 +/- 0.5℃ ranges respectively where sweating nor shivering was observed → subjects were cooled using venous injection and warmed using forced air warming
  Null zone is adjustable based on certain physiological states such as hypoglycemia, dehydration, injection of anesthetics → all adjust null zone range by affect shivering, sweating, or both thresholds for thermoregulatory response