Primary somatosensory cortex - wikipedia Primary somatosensory cortex Primary somatosensory cortex Primary somatosensory cortex labeled in purple Anatomical terms of neuroanatomy ( edit on Wikidata ) The primary somatosensory cortex is located in the postcentral gyrus, and is part of the somatosensory system. It was initially defined from surface stimulation studies of Wilder Penfield, and parallel surface potential studies of Bard, Woolsey, and Marshall. Although initially defined to be roughly the same as Brodmann areas 3, 1 and 2, more recent work by Kaas has suggested that for homogeny with other sensory fields only area 3 should be referred to as `` primary somatosensory cortex '', as it receives the bulk of the thalamocortical projections from the sensory input fields. At the primary somatosensory cortex, tactile representation is orderly arranged ( in an inverted fashion ) from the toe ( at the top of the cerebral hemisphere ) to mouth ( at the bottom ). However, some body parts may be controlled by partially overlapping regions of cortex. Each cerebral hemisphere of the primary somatosensory cortex only contains a tactile representation of the opposite ( contralateral ) side of the body. The amount of primary somatosensory cortex devoted to a body part is not proportional to the absolute size of the body surface, but, instead, to the relative density of cutaneous tactile receptors on that body part. The density of cutaneous tactile receptors on a body part is generally indicative of the degree of sensitivity of tactile stimulation experienced at said body part. For this reason, the human lips and hands have a larger representation than other body parts. Contents 1 Structure 1.1 Brodmann areas 3, 1 and 2 2 Clinical significance 3 See also 4 Additional images 5 References 6 External links Structure Primary somatosensory cortex labeled in green S1 Brodmann areas 3, 1 and 2 Brodmann areas 3, 1, and 2 make up the primary somatosensory cortex of the human brain ( or S1 ). Because Brodmann sliced the brain somewhat obliquely, he encountered area 1 first ; however, from anterior to posterior, the Brodmann designations are 3, 1, and 2, respectively. Brodmann area ( BA ) 3 is subdivided into areas 3a and 3b. Where BA 1 occupies the apex of the postcentral gyrus, the rostral border of BA 3a is in the nadir of the Central sulcus, and is caudally followed by BA 3b, then BA 1, with BA 2 following and ending in the nadir of the postcentral sulcus. BA 3b is now conceived as the primary somatosensory cortex because 1 ) it receives dense inputs from the NP nucleus of the thalamus ; 2 ) its neurons are highly responsive to somatosensory stimuli, but not other stimuli ; 3 ) lesions here impair somatic sensation ; and 4 ) electrical stimulation evokes somatic sensory experience. BA 3a also receives dense input from the thalamus ; however, this area is concerned with proprioception. Areas 1 and 2 receive dense inputs from BA 3b. The projection from 3b to 1 primarily relays texture information ; the projection to area 2 emphasizes size and shape. Lesions confined to these areas produce predictable dysfunction in texture, size, and shape discrimination. Somatosensory cortex, like other neocortex, is layered. Like other sensory cortex ( i.e., visual and auditory ) the thalamic inputs project into layer IV, which in turn project into other layers. As in other sensory cortices, S1 neurons are grouped together with similar inputs and responses into vertical columns that extend across cortical layers ( e.g., As shown by Vernon Mountcastle, into alternating layers of slowly adapting and rapidly adapting neurons ; or spatial segmentation of the vibrissae on mouse / rat cerebral cortex ). This area of cortex, as shown by Wilder Penfield and others, is organized somatotopically, having the pattern of a homunculus. That is, the legs and trunk fold over the midline ; the arms and hands are along the middle of the area shown here ; and the face is near the bottom of the figure. While it is not well - shown here, the lips and hands are enlarged on a proper homunculus, since a larger number of neurons in the cerebral cortex are devoted to processing information from these areas. The positions of Brodmann areas 3, 1, and 2 are - from the nadir of the central sulcus toward the apex of the postcentral gyrus - 3a, 3b, 1, and 2, respectively. These areas contain cells that project to the secondary somatosensory cortex. Clinical significance Lesions affecting the primary somatosensory cortex produce characteristic symptoms including : agraphesthesia, astereognosia, hemihypesthesia, and loss of vibration, proprioception and fine touch ( because the third - order neuron of the medial - lemniscal pathway can not synapse in the cortex ). It can also produce hemineglect, if it affects the non-dominant hemisphere. Destruction of brodmann area 3, 1, and 2 results in contralateral hemihypesthesia and astereognosis. It could also reduce nociception, thermoception, and crude touch, but, since information from the spinothalamic tract is interpreted mainly by other areas of the brain ( see insular cortex and cingulate gyrus ), it is not as relevant as the other symptoms. See also List of regions in the human brain Additional images Drawing to illustrate the relations of the brain to the skull. Sensory homunculus of the human brain. Cerebrum. Lateral view. Deep dissection. References Jump up ^ Viaene A.N. ; et al. ( 2011 ). `` synaptic properties of thalamic input to layers 2 / 3 and 4 of primary somatosensory and auditory cortices ''. Journal of Neurophysiology. 105 ( 1 ) : 279 -- 292. doi : 10.1152 / jn. 00747.2010. External links ancil - 1040 at NeuroNames - area 1 ancil - 1041 at NeuroNames - area 2 ancil - 1042 at NeuroNames - area 3 Anatomy of the cerebral cortex of the human brain Frontal lobe Superolateral Prefrontal Superior frontal gyrus 6 8 Middle frontal gyrus 9 10 46 Inferior frontal gyrus : 11 47 - Pars orbitalis Broca 's area 44 - Pars opercularis 45 - Pars triangularis Superior frontal sulcus Inferior frontal sulcus Precentral Precentral gyrus Precentral sulcus Medial / inferior Prefrontal Superior frontal gyrus 6 Medial frontal gyrus 8 9 Paraterminal gyrus / Paraolfactory area 12 Straight gyrus 11 Orbital gyri / Orbitofrontal cortex 10 11 12 Ventromedial prefrontal cortex 10 Subcallosal area 25 Olfactory sulcus Orbital sulcus Precentral Paracentral lobule Paracentral sulcus Both Primary motor cortex Premotor cortex 6 Supplementary motor area 6 Supplementary eye field 6 Frontal eye fields 8 Parietal lobe Superolateral Superior parietal lobule 5 7 Inferior parietal lobule 40 - Supramarginal gyrus 39 - Angular gyrus Parietal operculum 43 Intraparietal sulcus Medial / inferior Paracentral lobule 5 Precuneus 7 Marginal sulcus Both Postcentral gyrus / Primary somatosensory cortex Secondary somatosensory cortex 5 Posterior parietal cortex 7 Occipital lobe Superolateral Occipital pole of cerebrum Lateral occipital gyrus 18 19 Lunate sulcus Transverse occipital sulcus Medial / inferior Visual cortex 17 Cuneus Lingual gyrus Calcarine sulcus Temporal lobe Superolateral Transverse temporal gyrus / Auditory cortex 41 42 Superior temporal gyrus 38 22 / Wernicke 's area Middle temporal gyrus 21 Superior temporal sulcus Medial / inferior Fusiform gyrus 37 Medial temporal lobe 27 28 34 35 36 Inferior temporal gyrus 20 Inferior temporal sulcus Interlobar sulci / fissures Superolateral Central ( frontal + parietal ) Lateral ( frontal + parietal + temporal ) Parieto - occipital Preoccipital notch Medial / inferior Longitudinal fissure Cingulate ( frontal + cingulate ) Collateral ( temporal + occipital ) Callosal sulcus Limbic lobe Parahippocampal gyrus anterior Entorhinal cortex Perirhinal cortex Postrhinal cortex Posterior parahippocampal gyrus Prepyriform area Cingulate cortex / gyrus Subgenual area 25 Anterior cingulate 24 32 33 Posterior cingulate 23 31 Isthmus of cingulate gyrus : Retrosplenial cortex 26 29 30 Hippocampal formation Hippocampal sulcus Fimbria of hippocampus Dentate gyrus Rhinal sulcus Other Supracallosal gyrus Uncus Amygdala Insular cortex Insular cortex General Operculum Poles of cerebral hemispheres Some categorizations are approximations, and some Brodmann areas span gyri. Brain and spinal cord : neural tracts and fasciculi Sensory / ascending PCML 1 ° : Pacinian corpuscle / Meissner 's corpuscle → Posterior column ( Gracile fasciculus / Cuneate fasciculus ) → Gracile nucleus / Cuneate nucleus 2 ° : → sensory decussation / arcuate fibers ( Posterior external arcuate fibers, Internal arcuate fibers ) → Medial lemniscus / Trigeminal lemniscus → Thalamus ( VPL, VPM ) 3 ° : → Posterior limb of internal capsule → Postcentral gyrus Anterolateral / pain Fast / lateral 1 ° ( Free nerve ending → A delta fiber ) → 2 ° ( Anterior white commissure → Lateral and Anterior Spinothalamic tract → Spinal lemniscus → VPL of Thalamus ) → 3 ° ( Postcentral gyrus ) → 4 ° ( Posterior parietal cortex ) 2 ° ( Spinomesencephalic tract → Superior colliculus of Midbrain tectum ) Slow / medial 1 ° ( Group C nerve fiber → Spinoreticular tract → Reticular formation ) → 2 ° ( MD of Thalamus ) → 3 ° ( Cingulate cortex ) Motor / descending Pyramidal flexion : Primary motor cortex → Posterior limb of internal capsule → Decussation of pyramids → Corticospinal tract ( Lateral, Anterior ) → Neuromuscular junction Extrapyramidal flexion : Primary motor cortex → Genu of internal capsule → Corticobulbar tract → Facial motor nucleus → Facial muscles flexion : Red nucleus → Rubrospinal tract extension : Vestibulocerebellum → Vestibular nuclei → Vestibulospinal tract extension : Vestibulocerebellum → Reticular formation → Reticulospinal tract Midbrain tectum → Tectospinal tract → muscles of neck Basal ganglia direct : 1 ° ( Motor cortex → Striatum ) → 2 ° ( GPi ) → 3 ° ( Lenticular fasciculus / Ansa lenticularis → Thalamic fasciculus → VL of Thalamus ) → 4 ° ( Thalamocortical radiations → Supplementary motor area ) → 5 ° ( Motor cortex ) indirect : 1 ° ( Motor cortex → Striatum ) → 2 ° ( GPe ) → 3 ° ( Subthalamic fasciculus → Subthalamic nucleus ) → 4 ° ( Subthalamic fasciculus → GPi ) → 5 ° ( Lenticular fasciculus / Ansa lenticularis → Thalamic fasciculus → VL of Thalamus ) → 6 ° ( Thalamocortical radiations → Supplementary motor area ) → 7 ° ( Motor cortex ) nigrostriatal pathway : Pars compacta → Striatum Cerebellar Afferent Vestibular nuclei → Vestibulocerebellar tract → ICP → Cerebellum → Granule cell Pontine nuclei → Pontocerebellar fibers → MCP → Deep cerebellar nuclei → Granule cell Inferior olivary nucleus → Olivocerebellar tract → ICP → Hemisphere → Purkinje cell → Deep cerebellar nuclei Efferent Dentate nucleus in Lateral hemisphere / pontocerebellum → SCP → Dentatothalamic tract → Thalamus ( VL ) → Motor cortex Interposed nucleus in Intermediate hemisphere / spinocerebellum → SCP → Reticular formation, or → Cerebellothalamic tract → Red nucleus → Thalamus ( VL ) → Motor cortex Fastigial nucleus in Flocculonodular lobe / vestibulocerebellum → Vestibulocerebellar tract → Vestibular nuclei Bidirectional : Spinocerebellar Unconscious proprioception lower limb → 1 ° ( muscle spindles → DRG ) → 2 ° ( Posterior thoracic nucleus → Dorsal / posterior spinocerebellar tract → ICP → Cerebellar vermis ) upper limb → 1 ° ( muscle spindles → DRG ) → 2 ° ( Accessory cuneate nucleus → Cuneocerebellar tract → ICP → Anterior lobe of cerebellum ) Reflex arc lower limb → 1 ° ( Golgi tendon organ ) → 2 ° ( Ventral / anterior spinocerebellar tract → SCP → Cerebellar vermis ) upper limb → 1 ° ( Golgi tendon organ ) → 2 ° ( Rostral spinocerebellar tract → ICP → Cerebellum ) Retrieved from `` https://en.wikipedia.org/w/index.php?title=Primary_somatosensory_cortex&oldid=793227435 '' Categories : Cerebral cortex Brodmann areas Somatosensory system Parietal lobe Hidden categories : Articles which use infobox templates with no data rows All articles with unsourced statements Articles with unsourced statements from March 2013 Talk Contents About Wikipedia Add links This page was last edited on 31 July 2017, at 12 : 45. 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Question: where is the primary somatosensory cortex located in the brain
Answer: the postcentral gyrus