Primary Somatosensory Cortex - Wikipedia

Region of the brain which processes touch

Primary somatosensory cortex
Primary somatosensory cortex labeled in purple
Primary somatosensory cortex: second image.
Anatomical terms of neuroanatomy[edit on Wikidata]

In neuroanatomy, the primary somatosensory cortex is located in the postcentral gyrus of the brain's parietal lobe, 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.[1]

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 located on that body part (sometimes pictures as a cortical homunculus). 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.

Structure

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Brodmann areas 3, 1, and 2

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Brodmann areas 3, 1, and 2 make up the primary somatosensory cortex of the human brain (or S1).[2] 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 two cytoarchitectonic areas labeled as 3a and 3b.[3][4]

Clinical significance

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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 cannot 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.[citation needed]

See also

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• List of regions in the human brain

References

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1. ^ 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. PMC 3023380. PMID 21047937.
2. ^ Guy-Evans, Olivia. "Somatosensory Cortex". SimplyPsychology. Retrieved 22 February 2023.
3. ^ Benarroch, Eduardo E. (2006). Basic Neurosciences with Clinical Applications. Elsevier Health Sciences. p. 440. ISBN 0750675365. Retrieved 22 February 2023.
4. ^ Sanchez-Panchuelo, Rosa M.; Besle, Julien; Beckett, Alex; Bowtell, Richard; Schluppeck, Denis; Francis, Susan (2012-11-07). "Within-Digit Functional Parcellation of Brodmann Areas of the Human Primary Somatosensory Cortex Using Functional Magnetic Resonance Imaging at 7 tesla". The Journal of Neuroscience. 32 (45): 15815–15822. doi:10.1523/JNEUROSCI.2501-12.2012. ISSN 0270-6474. PMC 6621625. PMID 23136420.

External links

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• ancil-1040 at NeuroNames - area 1
• ancil-1041 at NeuroNames - area 2
• ancil-1042 at NeuroNames - area 3

v t e Anatomy of the cerebral cortex of the human brain
Frontal lobe	Superolateral Prefrontal Superior frontal gyrus 4 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 4 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 4 Paracentral sulcus Both Primary motor cortex 4 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 1 2 3 5 Precuneus 7 Marginal sulcus Both Postcentral gyrus/Primary somatosensory cortex 3, 1 and 2 Secondary somatosensory cortex 5 Posterior parietal cortex 7
Occipital lobe	Superolateral Occipital pole of cerebrum Occipital gyri 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 and 42 Superior temporal gyrus 38 22/Wernicke's area (Planum temporale) Superior temporal sulcus Middle temporal gyrus 21 Medial/inferior Occipitotemporal sulcus Fusiform gyrus 37/Fusiform face area Visual word form area Medial temporal lobe 27 28 34 35 36 Inferior temporal sulcus Inferior temporal gyrus 20
Interlobarsulci/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 Indusium griseum Uncus Amygdala
Insular cortex	Insular cortex
General	Operculum Poles of cerebral hemispheres
Some categorizations are approximations, and some Brodmann areas span gyri.

v t e Brain and spinal cord: neural tracts and fasciculi
Sensory	DCML 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	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)