Somatosensory cortex
The somatosensory or somatosensitive cortex ( ancient Greek σώμα soma , German 'body' ; Latin sensorius 'serving sensation' , sensibilis ' capable of feeling ' , cortex 'cortex' ) is the circumscribed part of the cerebral cortex that is used for the central processing of haptic perception . The information comes either from receptors in the skin , which receive a variety of environmental stimuli there ( exteroception ), or it enables the body to perceive itself through receptors inside the body ( proprioception ). The sensory modalities processed in the somatosensory cortex are touch, pressure, vibration and temperature; this also applies to some extent to pain sensations .
However, not all mechanical and physical stimuli are implemented here; already at the level of the spinal cord there are neural circuits that trigger simple (usually escape) movements without any action on the part of the brain: the reflexes .
From a functional point of view, the somatosensory cortex belongs to the Neolemniscus and is its end point.
Classification and location
It is divided into the primary-sensitive areas ( S1 , Brodmann areas areas 1, 2 and 3 , later a subdivision into 3a and 3b) and the secondary-sensitive or sensitive association areas ( S2 , corresponding to areas 40 and 43 ). The majority of the primarily sensitive cortex in humans lies on the postcentral gyrus , the first cerebral convolute behind the central groove . The secondary fields connect to the rear ( posterior ) and below ( ventral , S2).
construction
The somatosensory cortex belongs to the six-layer isocortex . The accentuated inner granular cell layer is histologically conspicuous and is particularly pronounced in area 3b, so that the latter is also referred to as the coniocortex . The primary-sensitive cortex in particular - like the immediately adjacent primary-motor cortex - is structured in a strictly somatotopic manner. This means that neighboring zones of the body are also here next to each other. This creates an image of the body on the cerebral cortex, the so-called homunculus , which is distorted according to the respective weighting . The representations of the hand, fingers, face and lips are particularly extensive. There is probably a separate somatotopia for each of the four areas of S1 and the sub-areas of S2, which, however, is sometimes blurred, sometimes even with a double representation of body parts (e.g. the hand in area 2).
Neural connections
The afferents (inputs) of the somatosensory cortex ultimately come from different sensory cells or organs that are distributed over the entire body in different densities. The afferent pathways are synaptically switched several times : from the actual sensory cell to pseudounipolar nerve cells , whose cell somata are located in the spinal ganglia of the posterior root , in the dorsal core to the second and in the thalamus to the third neuron. For the sensitivity of the face, the path runs analogously over the fifth cranial nerve ( trigeminal nerve ), is switched in the Gasseri ganglion the first time and in the trigeminal nucleus in the brain stem the second time and also reaches the thalamus. This centropetal orbit is in its entirety - including the sensory cortex - called the lemniscale system . A second, fundamentally different system of sensory conduction is the spinothalamic tract , but only a very small part of it reaches the thalamus and thus the cerebral cortex.
Efferents (exits) from the somatosensory cortex mainly reach associative areas of the same ( ipsilateral ) and via the corpus callosum of the other ( contralateral ) hemisphere of the cerebrum. Other pathways return to the thalamus, via the pons into the cerebellum , into the basal ganglia and into the spinal cord . There are also fibers that contribute to the pyramidal trajectory.
See also
literature
- Otto Detlev Creutzfeldt : Cortex cerebri. Springer, 1983, ISBN 3-540-12193-5 .
- K. Zilles, G. Rehkämper: Functional Neuroanatomy. Springer, Berlin 1993, ISBN 3-540-54690-1 .
- D. Drenckhahn, W. Zenker: Benninghoff. Anatomy. Urban & Schwarzenberg, Munich 1994, ISBN 3-541-00255-7 .
