NBME 17 Area marked "G" (NBME Answers)

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submitted by ∗bingcentipede(356)

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G represents the primary somatosensory area of the parietal lobe. The stem describes a 69 (nice) year old woman with sensory issues on the left side. She presents w/ a Babinski sign on the left, decreased somatic sensation in the left foot, agraphesthesia (when you "draw" a number on someone's skin and they can't interpret it) on the plantar surfaces of the toes, decreased position sense in the toes. The question says there is an edematous area in the cerebral cortex of the right hemisphere.

I had trouble with this, but I think it's describing somatosensory because of the sensory problems. Don't understand the UMN lesion (Babinski). Here's what Wikipedia says: "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."

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mittelschmerz The Babinski tripped me up too, here's what I found: "Sixty percent of the CST fibers originate from the primary motor cortex, premotor areas, and supplementary motor areas. The remainder originates from primary sensory areas, the parietal cortex, and the operculum. Damage anywhere along the CST can result in the presence of a Babinski sign." from https://www.ncbi.nlm.nih.gov/books/NBK519009/ +18

yourmomsbartholincyst I think this question is more simply about the topographical arrangement of the homunculus (which I once again somehow managed to flip backwards during the exam). Lower extremity is topographically mapped to more medial portions of the somatosensory cortex, hence letter G and why ACA strokes tend to affect the LE more. Homunculus, our favorite hunk, FA2020 pg 502 +17

j44n youre occluding the MCA blow flow from the MCA flows front to back so if you occlude the section that provides blood flow to the precentral gyrus you will also occlude the section that supplies the sensory portion http://what-when-how.com/neuroscience/blood-supply-of-the-central-nervous-system-gross-anatomy-of-the-brain-part-1/ +

j44n excuse me i miss spoke its the ACA because its her legs, look at figure 4-2 in the link on my previous comment +

j44n so if you have motor and sensory the infarct is in the portion that belongs to the motor portion, if you have sensory only youve occluded the artery more distally +

jy1544 I thought G was indicating the primary motor cortex in the frontal lobe from a medial view (anterior to the central sulcus), hence the weakness - and the sensory disturbances were due to edema affecting the adjacent somatosensory cortex https://web.duke.edu/brain/siteParts/images/fig1-5_2018.jpg +9

juhee From medial sagittal view of brain, the sulcus between G and H was marginal sulcus (not central sulcus). It is extension of cingulate sulcus. And it is an excellent landmark to help confirm the location of the central sulcus, which is located one sulcus anterior to the marginal sulcus. So G is indicating the primary somatosensory cortex. Here's the image. https://prod-images-static.radiopaedia.org/images/30139451/e006b3135364e41e213e83fc2a99ac_gallery.jpeg +

chaosawaits This is purely a homunculus question. Any further thought into it is just overkill. +