In simple or layman’s terms, the body feels cold through the somatosensory system; a system associated with touch. Now while this is a simple definition – there is a whole bunch of complex parts, components and mechanics that go into the making of this system. Like a machine or maybe a factory, the somatosensory system can be divided into three stages – input, processes and outputs. And there are many parts that make these operations possible. The massive network of nerve endings carpet the skin all over and enable the individual to feel different tactile sensations – heat, cold, pain, textures and even vibrations.
To understand how the skin and the somatosensory system work, it would be relevant to see the structure of the skin.
If one were to take a cross section of the skin, then it is easy to see the many layers that go into its making. Truly, the somatosensory system is a marvel of engineering that the body use to protect itself from so many external factors and influences. The layer that is visible to everyone is the outermost layer or the ‘epidermis.’ This waterproof layer is going through constant cycles of “refresh”, with dead skin cells sloughing off and being replaced by new ones.
Going inwards, the second layer is the ‘dermis.’ This is the layer that supplies nutrients to the epidermis. It is loaded in nerve cells, blood vessels and nerve endings as well. The last layer is the subcutaneous tissue, which has the fat and connective tissue. One of the biggest functions that this layer performs is the regulation of body temperature and shock absorption.
The Components of the Somatosensory System
This system is built on four pillars, if one can call it that. These pillars are essentially different types of receptors. A sensory receptor is a nerve ending, which reacts to every stimulus that it comes in contact with. These receptors can, therefore, respond to thermal inputs, the “feel” of different things and stimuli that cause pain. The four receptors that are kind of super specialists in their jobs are:
Each one of these receptors does its job in keeping the skin alive to the sensations. For the scope of this article, it would be useful to focus on the second pillar and that is the thermoreceptor.
So how does the body know when to feel cold?
One of the components of the somatosensory system, the thermoreceptor is responsible for the body to feel the sensation of cold. These receptors lie in the dermis layer of the skin. They are classified into hot and cold receptors. The cold receptors kick in when the skin’s surface dips below 95 degree Fahrenheit (or 308.15 Kelvin or 35 degree Celsius). They go into the non-stimulated mode when the body surface temperature dips below 41 degree Fahrenheit (or 5 degree Celsiusor 278.15 Kelvin). This non-stimulated mode can be visualised when one thinks of the fact that the body goes numb in extreme cold weather.
The receptors that are responsible for feeling cold also outnumber those, which are responsible for hot sensations. Interestingly, the greatest number of cold receptors is located in the ears and face and, therefore, covering up these extremities gets the body to feel warmer quickly. The entire process of feeling cold takes place with the external stimulus being transmitted through neurons and the central nervous system, and then the body being told that it is cold – all of it in less than the blink of an eye.