|Brain: Postcentral gyrus|
|Postcentral gyrus of the human brain.|
|Brodmann areas 3, 1 and 2 of human brain. Brodmann area 3 is in red, area 1 in green, and area 2 in yellow.|
|Gray's||subject #189 823|
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.
The lateral postcentral gyrus is bounded by:
- medial longitudinal fissure medially (to the middle)
- central sulcus rostrally (in front)
- postcentral sulcus caudally (in back)
- lateral sulcus inferiorly (underneath)
It is the location of primary somatosensory cortex, the main sensory receptive area for the sense of touch. Like other sensory areas, there is 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 is not 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.
Lesions affecting the primary somatosensory cortex produce characteristic symptoms including: agraphesthesia, astereognosia, loss of vibration, proprioception and fine touch (because the third neuron of the medial-lemniscal pathway cannot do its 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 is not as relevant as the other symptoms.
- Sensory and motor homunculi.jpg
Sensory and motor homunculi.
- Homunculus sensory.png
Sensory homunculus of the human brain.