Medical science summarizes the ability to epicritic and protopathic perception of pain, temperature, and mechanical stimuli on the skin as surface sensitivity of the sense of touch. The perceptions are relevant to the tactile as well as the haptic. Disorders of sensitivity are usually due to nerve lesions.
What is surface sensitivity?
Medical science summarizes the ability to epicritical and protopathic perception of pain, temperature, and mechanical stimuli on the skin as surface sensitivity of the sense of touch. The sense of touch is also called the skin sense. This is one of five human perceptual instances. The skin sense serves primarily for exteroception, but in the case of mucous membranes it can also serve for interoception. The perception of stimuli from one’s own body thus falls just as much within the system’s area of responsibility as that of stimuli from the environment. The skin sense enables humans to passively and actively perceive pressure, pain and temperatures. The active part is called haptic and the passive part tactile perception. The perceptual qualities of the sensory structure can be differentiated according to various aspects, such as the type of stimulus, the site of excitation, centripetal transmission, and the wiring in different core areas. Based on the type of stimulus, medicine distinguishes surface sensitivity into nociception for pain perception, thermoreception for temperature perception, and mechanoreception for pressure, temperature, vibration, and stretch. Surface sensitivity refers to both the percepts of mechanoreception and the impressions of nociception and thermoreception. Surface sensitivity is interconnected into different core areas and includes both protopathic gross perception and epicritic fine perception.
Function and task
Surface sensitivity is the most important quality of the skin sense. It is made possible by different receptors, which are free nerve endings located in the skin layers. These receptors are each specialized to bind to a specific stimulus molecule. Mechanoreceptors are distinguished in this context from thermoreceptors and nociceptors. These sensory cells translate stimuli such as pressure, pain or temperature into the language of the central nervous system (CNS). The sensors transform the stimuli into an action potential and transmit them to the CNS via afferent pathways. In humans, tactile perception is primarily attached to the mechanoreceptors of the skin. The individual receptors of this group are, for example, the Merkel cells and the Ruffini, Vater-Pacini and Meissner corpuscles. It is through these receptors that humans are able, for example, to sense sustained pressure loads and stretching. The perceptions of the mechanoreceptors correspond to epicritical perception. Information from epicritic mechanoreceptors in the area of surface sensitivity travels via class Aβ nerve fibers toward the central nervous system. The individual fibers run without crossing in the fasciculi, or posterior cord pathway, of the spinal cord. Protopathic sensations of temperature and pain by the thermoreceptors and pain receptors contribute to surface sensitivity. These percepts travel to the central nervous system via afferent class Aδ and C nerve fibers and are subject to mediation by free nerve terminals. Immediately after entering the posterior horn of the spinal cord, the fibers of the protopathic pathways cross to the contralateral side, where they ascend into the tractus spinothalamicus anterior et lateralis. In the brain, the percepts from the individual receptors are processed into an overall perception. This process corresponds to sensory integration and gives the person an overall impression of the stimuli currently acting on them. Surface sensitivity has its own memory that helps the brain filter, interpret, evaluate, and classify percepts. For both active haptics and passive tactile, surface sensitivity, with its qualities of pain, temperature, and mechanical, is a crucial component.
Diseases and discomfort
Neurology distinguishes surface sensitivity disorders into hyperesthesias, anesthesias, hypesthesias, and paresthesias. Hyperesthesia corresponds to exaggerated surface sensitivity. An increased tactile perception is also called tactile defense in medicine.The hypersensitivity evokes a defensive attitude in the patient, so to speak. The affected person avoids tactile stimuli such as touch. They often withdraw not only from being touched by other people, but also from touching certain materials such as sand, dust, mud, paste or felt and surfaces such as metal or wood. The reason for this is usually pain perception on the skin caused by hyperesthesia. The opposite of hyperesthesias are hypesthesias. These are diminished sensations that usually correspond to a dull feeling on the skin. In so-called anasthesias, on the other hand, the patient’s surface sensitivity is completely absent and the affected skin areas are completely numb. Missensations, known as paresthesias, are to be distinguished from this phenomenon. For example, paraesthesia can be expressed as a tingling sensation or a burning sensation. A cold stimulus on the skin is sometimes mistaken by patients for a scalding hot stimulus. All of the above-mentioned surface sensitivity disorders are associated primarily with nerve damage. Especially when the pathways in the central nervous system are affected, only insufficient information from the area of surface sensitivity reaches the brain. This type of nerve damage involves central nervous lesions, which can sometimes be traumatic. Tumors or neurological diseases such as multiple sclerosis are also possible causes. Equally well, a disturbance of surface sensitivity can be due to the processing centers in the brain. Such damage can be caused by strokes or ischemia. Inflammation-related brain lesions are also a possibility. In some circumstances, a disorder of surface sensitivity may also be due to a lack of sensory integration. Sensory integration disorders often result from a genetic predisposition and may be alleviated by certain training methods.
