The sensitivity in the cerebral cortex

The main sensitive area in the cerebral cortex is back Central gyrus (kernel skin analyzer, according to Pavlov)associated with the innervation of various parts of the body - somatic sensitive area I. There is also a sensitive area II - a small area covering a part of the lower cut back Central gyrus and the back part of the upper lip silvavoc furrows, and zone III - on the medial surface of the hemisphere, posterior to the Central gyrus. Basically, all the sensitivity presents the contralateral peripheral stimulation. However, the experiments indicate the presence of bilateral innervation in the cortex.
In the back Central gyrus there somatotropina projection of skin receptors, respectively certain body parts: the upper part contains sensitive zones of the feet, then down areas of the torso, arms and head. When cortical area of innervation to the distal segments of the feet and hands (and in the last of the big toe) is greater than the zone of proximal segments of the limbs and trunk. Similarly, in the cortical area of innervation face the highest ranks field associated with sensitivity around the mouth area. Schematically the location of cortical projection zones of sensitivity from various parts of the body is represented in the form of a "man" upside down (Fig. 3). In the back Central gyrus sensitivity presented by segment, dermatomes principle. In the clinic defeat back Central gyrus, there are skin zone gipestesia on the opposite side of the body, respectively specified somatotopic.
You can observe two basic types of sensitivity disorders: vertical circular type and radicular-segmental. Vertically-circular - type reduction or loss of sensitivity in certain areas of the body, limbs with circular going abroad. Features of somatic projections explain the peculiar different disorders of sensitivity, typical only for the cortical pathology, for example hypoesthesia in the lip area (one half) and thumb, bilateral loss of sensation in the feet when paracentral defeat, and so on, Radicular segmental type is characterized by a loss of sensitivity only on the inside or the outside of the corresponding limb. Sensitivity of the inner side of a limb in cortical area is represented in more front; the sensitivity of the outside - in the back of the departments. With extensive lesions back Central gyrus, and the top parietal cortex, which does not somatotropina projection, there hypoesthesia the opposite side of the body with the prevalence of disorders of sensitivity in the distal limb segments. Usually hypoesthesia is volatile, unstable, not always quite certain character, revealing the tendency to restitution. Sometimes you can detect the reduction of surface sensitivity and homolateral side.
Violations of muscle and joints sensitivity with the defeat of cortical sensitive areas are generally more pronounced, more upright than violation of the surface, and is registered only in the opposite hearth side. There is also upset vibration sensitivity.
With the defeat of sensitive areas of the cortex are commonly reported violations of a number of special, cortical, more sophisticated types of sensitivity. This includes violation of recognition of the difference in the intensity of various, including skin, irritation, two-dimensional spatial (topographia) and three-dimensional spatial sensitivity (astereognosis). Primary and cortical astereognosis occurs when the defeat mainly lower parietal region. However there are also violations of recognition and guidance in respect of parts of its own body and their position in space - disorder scheme of the body (see). There are also violations of recognition of parts of its body - autotopology, distinguish right and left side, the corresponding arrangement of parts of the body in space, head of the fingers (the so-called finger agnosia), etc. are Possible and distorted perception of the body, feelings false change their form and location, the emergence of feelings of presence of excess, increased or decreased body parts (arms, legs, head and so on) until the feeling of the disappearance of the whole body - depersonalization. Manifestation of autotopology can also be the feeling of a lack of internal body (for example, unpleasant, painful feeling of the disappearance of the heart).
Violations schemes body is anosognosia - lack of perception of paralysis patients with hemiplegia, usually observed in the defeat of the right parietal lobe. Disorders of sensitivity observed with the defeat not only the back Central gyrus, the parietal lobe, but areas of the cerebral cortex, located to the front and to the back of it. This corresponds to the teaching of I. P. Pavlov's dynamic localization features. Cm. also the senses.

Fig. 3. Schematic arrangement of cortical projection zones skin sensitivity from various parts of the body in the form of a "man" (Penfillb, Badri). Relatively large sizes large fingers, hands, feet and lips meet more pronounced zone sensitive innervation for these parts of the body.