Temperature sensation (med. thermoreception) of the skin and mucous membranes is provided by thermoreceptors. These thermoreceptors are specialized nerve endings that project perceived temperature stimuli via chemical processes to nerve fibers in the spinal cord, from where the stimuli travel to the hypothalamus. The hypothalamus is the center of temperature regulation in the brain, where thermosensitive neurons take peripheral temperature information from the thermoreceptors and integrate it with central information about prevailing body temperature to initiate protective adaptations such as cold shivering or sweating. Temperature sensation can be impaired as a result of various neurological diseases, most notably multiple sclerosis, polyneuropathies, strokes, Lyme disease, and dementia.
What is temperature sensation?
Human temperature sensation is also known as thermoception and refers to the perceived ambient temperature. Human temperature sensation is also known as thermoception and refers to the perceived ambient temperature. Free nerve endings, known as receptors, give the dermis and epidermis of the skin and the mucous membranes of the viscera a specific surface sensitivity to external stimuli. These external stimuli include touch stimuli, pain stimuli, and temperature stimuli. In medicine, epicritic sensitivity of the skin refers to touch sensitivity by mechanoreceptors. Together with pain receptors, thermoreceptors, on the other hand, are responsible for potopathic sensitivity. Thermal and pain stimuli are received by the receptors of the potopathic system and transmitted to fibers of the central nervous system. These nerve fibers, or cord cells, are located in the contralateral side of the spinal cord posterior horn, extending into the anterior cord via the tractus spinothalamicus anterior et lateralis. From the spinal cord, perceived temperatures are eventually transmitted to the hypothalamus. Perceived temperature differs from person to person and never equals the actual ambient temperature. Thus, perceived temperatures are always subjective perceptions, related in particular to cultural background and the overall physiological and psychological state of the individual.
Function and task
Temperature perception plays a role in particular in the body’s protective reflexes and thermoregulation. The receptors of the skin each have a specific stimulus sensitivity. Depending on this stimulus sensitivity, the receptors are differentiated into cold and warm receptors. The cold receptors show a reaction to temperature ranges of 20 to 32 degrees Celsius, i.e. to temperatures below body temperature. They respond to descending temperatures with an increase in discharge frequency. Warm receptors, on the other hand, are responsible for the range between 32 and 42 degrees Celsius and perceive temperature changes within this range. The nerve endings generate certain action potentials depending on the temperature acting on them. Through chemical reactions, these action potentials are transmitted via the synapses to the nerve fibers of the spinal cord, from where they are passed on via neuronal switching points to the thermosensitive nerve cells of the brain. There, in the hypothalamus, lies the center of human thermoregulation. The body temperature is adjusted to the outside temperature via this center. The thermoregulatory center of the brain compares the thermal information of the periphery with the central temperature information of the body. On the basis of this comparison, the brain gives a thermoregulatory response and thus, in the case of hot temperatures, initiates heat loss through peripheral vasodilatation or sweating, for example. On the other hand, in the case of perceived cold, the response to the transmitted temperature stimuli can also correspond to heat production or heat conservation, for example in the form of skin coldness, increased metabolic activity or cold shivering. Through the respective response to the temperature sensation, the body prevents overheating and cooling. Human well-being is closely linked to the activity of thermoregulation, which in turn is closely linked to blood circulation.Both heat stress and cold stress strain the circulatory system, since in both cases an adjustment of body temperature must occur via changes in blood flow.
Diseases and ailments
Temperature sensation by heat and cold receptors of the skin may be disturbed or absent as a result of various, mostly neurological phenomena. This is then referred to as a sensitivity disorder. Polyneuropathies, for example, can damage nerve fibers of various localizations. If sensitive nerve fibers are damaged, to which the thermoreceptors of the skin project, then correspondingly disturbed temperature perceptions can occur. Sensitivity disorders of the skin can, however, also be symptomatic of the autoimmune disease multiple sclerosis, in which there is permanent immunologically induced inflammation in the central nervous system. In this case, an inflammation of the spinal cord areas for the transmission of thermal information can be just as responsible for a disturbed temperature sensation as an inflammation of the thermocenter in the hypothalamus. However, impaired temperature sensation in multiple sclerosis is usually accompanied by general sensory disturbances such as persistent numbness. Apart from this, diabetes can also be associated with impaired temperature sensation, especially in the area of the feet. Diabetes-related sensitivity disorders are often accompanied by a loss of muscle reflexes and are usually limited to a sock-shaped area of the foot. Long is the list of diseases that can be related to false temperature sensation. In addition to those mentioned, for example, Lyme disease, a prolapse of the sciatic nerve, dementia, stroke or migraine can also trigger the sensitivity disorder. On the other hand, disturbed temperature sensation does not necessarily have to have a physical or pathological cause in all cases. For example, exhaustion can also confuse temperature sensation. The same applies to psychological stress and mental illness. Disturbances of temperature sensation are usually more worrying if they are limited to a definable skin area and do not affect the entire body. If the localization can be precisely delimited, the disturbed sensitivity is usually not related to exhaustion or psychological stress, but actually to a disease.
