Protopathic Sensitivity: Function, Tasks, Role & Diseases

Protopathic sensitivity is the term used to describe gross perception as a sensory quality of the skin that detects threats to the vital sphere. In addition to pain and temperature, humans thus perceive mechanical stimuli that travel to the central nervous system via the tractus spinothalamicus. Associated complaints often derive from multiple sclerosis.

What is protopathic sensitivity?

Protopathic sensitivity is the term used to describe gross perception as a sensory quality of the skin that detects threats to the vital sphere. In addition to pain and temperature, humans perceive mechanical stimuli in this way. Sensibility can be further subdivided according to the nature of the stimulus, the site of excitation, centripetal transmission, and wiring into different core areas. The latter group includes protopathic, epicritic, and proprioceptive sensitivity. Protopathic sensitivity is also known as gross perception and encompasses all skin sensations that indicate a threat to the vital sphere. These include nociception, thermoreception, and grosser mechanoreception. Nociception corresponds to the perception of pain, thermoreception to the perception of temperature and mechanoreception to the perception of mechanical stimuli such as pressure. The sensory cells involved in the skin are either nociceptors, mechanoreceptors, or thermoreceptors. These sensory cells are open nerve endings that receive a stimulus and convert it into bioelectrical excitation. They translate the threat of the vital sphere into the language of the central nervous system. The receptors form an action potential only when a certain stimulus threshold is exceeded.

Function and task

The sense of skin or touch is one of five sensory systems in the human organism. Thanks to the skin, humans are sensitive to external stimuli such as pressure, touch, temperature and pain. In connection with the skin, active and passive sensory qualities are distinguished. The active qualities play a role in touching and are called the sense of touch. The passive qualities come under the term tactile. In addition to fine perception, the skin is capable of coarse perception. The fine perception corresponds to the tactile acuity and thus to the epicritical sensitivity, as it is decisive for the active responsibilities of the skin sense. Coarse perception of the skin, on the other hand, allows the human brain to detect threats to its own vital sphere and plays a role in the passive qualities of the system. Pain, temperature and mechanical stimuli can be tolerated up to a certain threshold. The body recognizes them above this threshold as a clear threat. The transmission of all protopathic information is then handled by the tractus spinothalamicus. The fiber bundles of this afferent nerve correspond to the tractus spinothalamicus lateralis for pain perception and temperature perception and to the tractus spinothalamicus anterior for the perception of gross touch impressions and tactile impressions. The afferents of the tractus spinothalamicus cross the commissura alba anterior immediately after entering the spinal cord and shift to the contralateral side. Protopathic impressions are polyneuronally connected. The first neuron of the wiring is located in the spinal ganglion. The second neuron is located in the posterior horn of the spinal cord. Immediately after switching from the first to the second neuron, the afferent crosses to the contralateral side. On this side, the pathway of the anterior cord runs into the brainstem. As the lemniscus spinalis, the pathway continues to the thalamus. In its nucleus ventralis posterolateralis the switch to the third neuron takes place. The axons of this third neuron extend through the capsula interna into the cerebral cortex (cortex cerebri). A fourth switch occurs in the sensory cortex (postcentral gyrus), which serves conscious perception. By far not all protopathic information is consciously perceived. The brain would be overloaded by the overload of stimuli. Probably for this reason, protopathic receptors do not generate an action potential for transmission to consciousness until a certain threshold is reached.

Diseases and complaints

Lesions of protopathic pathways are the concern of neurology. Most cases involve lesions of the lateral and anterior spinothalamic tracts. Isolated lesion of the anterior or lateral tracts are almost impossible because of the close spatial relationship.If one of the pathways is damaged, almost always all impressions of protopathic perception fail. In individual cases, the perceptions are only severely limited. The position of the lesion can be at any level between the first and the fourth neuron. Regardless of this, the deficits of protopathic perception can be identified exclusively on the associated body side of the first neuron. The tactile sensations are not necessarily impaired in lesions of this type. Thus, although the superior instance of the skin sense is capable of both active touch and passive sensation of impressions, lesions of the skin sense may differ depending on their location in the central nervous system. The active perceptual qualities of the skin correspond to epicritical sensitivity. This fine perception is wired in a different way than protopathic sensitivity. In individual cases, lesions may nevertheless affect both sensory qualities. A disease with both protopathic and epicritic lesions is multiple sclerosis (MS). This autoimmune disease causes immunologically induced inflammation in central nervous tissue and can leave permanent damage. Protopathic paresthesias are a common early symptom of the disease. For example, an MS patient may perceive cold water as scalding hot, and the same may be true in reverse. The simplest touches may be perceived as painful after MS-related lesions in the central nervous system. A feeling of heaviness in the limbs is also conceivable in relation to proprioceptive perception. MS is not the only neurological disease with effects on protopathic perception. Nonetheless, it is one of the most common diseases with protopathic impairment.