Everything about Primary Somatosensory Cortex totally explained
The lateral
postcentral gyrus is a prominent structure in the
parietal lobe of the human
brain and an important landmark. It was initially defined from surface stimulation studies of 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 received the bulk of the thalamocortical projection from the sensory input fields.
Postcentral gyrus
The lateral postcentral gyrus is bounded by:
It is the location of
primary somatosensory cortex, the main sensory receptive area for the sense of touch. Like other sensory areas, there's a map of sensory space called a
homunculus in this location. For the primary somatosensory cortex, this is called the
sensory homunculus. See a somewhat fanciful and highly schematic representation of the sensory homunculus below.
Brodmann areas 3, 1 and 2
Brodmann areas 3, 1 and 2 comprise the primary
somatosensory cortex of the human
brain. Because
Brodmann sliced the
brain somewhat obliquely, he encountered area 1 first; however, from
rostral to
caudal the
Brodmann designations are 3, 1 and 2, respectively.
This area of cortex, as shown by
Wilder Penfield and others, has 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 isn't well-shown here, the lips and hands are enlarged on a proper homunculus, since a large number of
neurons in the
cerebral cortex are devoted to processing information from these areas.
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, loss of
vibration,
proprioception and
fine touch (because the third-order neuron of the medial-lemniscal pathway can't synapse in the cortex). It can also produce
hemineglect, if it affects the non-dominant hemisphere.
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 isn't as relevant as the other symptoms.
Further Information
Get more info on 'Primary Somatosensory Cortex'.
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