Explain why the touch of an ice cube on the skin burns?

First cause: Body response to cold

When an ice cube comes into contact with the skin, the body immediately reacts to deal with the cold. This reaction is mainly due to the stimulation of sensory receptors under the skin. These special receptors, called thermoreceptors, are sensitive to changes in temperature and send signals to the brain to indicate a sudden drop in temperature. The brain interprets these signals as a sensation of cold and triggers a series of physiological responses to combat this unpleasant sensation.

One of the body's first responses to cold is vasoconstriction, which is the contraction of blood vessels located near the surface of the skin. This mechanism helps limit the loss of body heat to the outside by reducing blood flow in areas exposed to the cold. As a result, the skin becomes pale because less blood is circulating, and the sensation of cold is intensified.

At the same time, the body also activates the production of heat to maintain its internal temperature. Muscles begin to shiver, a phenomenon that generates heat by burning calories. This muscle tremor is an automatic response of the body to increase its temperature and combat the external cold. As the skin temperature decreases, the brain sends signals to intensify this heat production to restore the body's thermal balance.

In summary, the burning sensation felt when an ice cube touches the skin is the result of a cascade of complex physiological reactions triggered by the body's response to cold. These reactions aim to protect the body against the harmful effects of cold by maintaining its internal temperature within acceptable limits.

Second cause: Effect of temperature on cutaneous receptors

Temperature directly influences the cutaneous receptors present in the skin. These receptors are specialized nerve endings capable of detecting temperature changes. When an ice cube comes into contact with the skin, temperature receptors known as thermoreceptors are activated. These receptors send an electrical signal to the brain to indicate a sudden drop in temperature.

Thermoreceptors are sensitive to both cold and heat. When the skin temperature rapidly decreases following contact with an ice cube, the cutaneous receptors react by sending electrical signals along nerve pathways to the brain. This reaction is interpreted by the brain as a burning sensation, even though the ice cube itself does not produce heat.

Therefore, it is the activation of cutaneous receptors by the sudden temperature change caused by the ice cube contact that creates the burning sensation. Cutaneous receptors play an essential role in the perception of thermal stimuli and help the body regulate its internal temperature by reacting to external temperature variations.

Third cause: Thermal conduction between the ice cube and the skin.

Thermal conduction between the ice cube and the skin occurs when the ice cube, at a temperature much lower than that of the human body, comes into direct contact with the skin. This contact leads to a transfer of heat from the body to the ice cube, causing an intense sensation of cold. The temperature difference between the skin and the ice cube results in a flow of heat from the hottest point (the skin) to the coldest point (the ice cube). This heat transfer occurs quickly, as the ice cube has a high thermal conductivity, meaning it is able to efficiently transfer heat. The skin, on the other hand, has lower thermal conductivity, making it more sensitive to temperature changes. Therefore, thermal conduction between the ice cube and the skin contributes to the burning sensation felt when an ice cube is applied directly to the skin.