Question

Imagine that you place your left hand in cool water (10°C) and your right hand in warm water (40°C) for ten minutes. After a few minutes, you stop noticing that your hands are at different temperatures. Explain this phenomenon, using your knowledge of sensory neuron function. After ten minutes, both your hands are immersed in water at 50°C – and you scream in pain! This temperature now seems scalding hot to your left hand, but not your right hand. Why?

Answer 1

Left hand which is placed in 10 degrees centigrade cool water for ten minutes undergoes cutaneous vasoconstriction of the peripheral vessels which results in decreased heat loss, and when it is immersed in 50 degrees centigrade hot water , sudden change in the temperature of the fingers leads to scalds and severe pain as the skin is insensitive and numb for the last ten minutes due to cold water ,there is change in discharge from cutaneous cold receptors with change in temperatures due to hypothalamus that acts directly on the temperature receptors of the skin.Warm sensitive neurons are responsible for activating the heat dissipating pathways from the hypothalamus and this sensitivity activates the sensory nerve endings of the skin of the fingers which results in scalds and pain.Temperature change increases the discharge of one group while simulataneously decreasing the other.The neurons in the hypothalamus alters their firing rates in response to peripheral warming and cooling while a few others have been found to increase their activity in response to both heat and cold peripheral sensations.

Right hand gets accommodated to hot at 40 degrees centigrade hot water,though this is little higher for the skin sensitivity,and when the hand is shifted to 50 degrees centigrade hot water,the warm sensitive receptors of the skin are already active and they dessipate heat pathways from the hypothalamus.