Chapter 12. Somatotopic Cortical Maps
12.1 Title slide
Demonstration 12.4
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Somatotopic Cortical Maps
Apply tactile stimuli to a human figure and see where signals are received in the somatosensory cortex.
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Stimulation of the somatosensory receptors in a body part sends signals to a specific part of the somatosensory cortex. Proportionally larger areas of the somatosensory cortex are devoted to receiving signals from body parts with higher spatial resolution of touch. The shoulders have relatively low spatial resolution of touch, so the person being massaged in this photo will probably be able to discriminate the touch of the thumb but not of the other individual fingers.
Photo: GIPhotoStock / Science Source.
Photo: GIPhotoStock / Science Source.
What Are Somatotopic Cortical Maps?
The somatosensory cortex is located in the postcentral gyrus, a strip at the anterior (front) of the parietal lobe, just behind the central sulcus. It consists of two main subregions—the primary somatosensory cortex (or S1) and the secondary somatosensory cortex (or S2). S1 is itself divided into four side-by-side strips—known as areas 3a, 3b, 1, and 2.
Studies have shown that, within any small region of any of the areas and subareas of the somatosensory cortex, adjacent locations receive tactile signals from adjacent locations on the body surface, forming a somatotopic map on the cortex, but a map that is somewhat disarranged and distorted. It’s disarranged in that larger adjacent regions of the cortex don't necessarily receive signals from adjacent parts of the body—for example, the cortical region that receives signals from the face is adjacent to the region that receives signals from the hand and fingers. And it’s distorted in that relatively more cortical space is devoted to receiving signals from body parts where sensory receptors are densely distributed and have small receptive fields, such as the fingertips and lips, while relatively less space is devoted to body parts with fewer receptors that have larger receptive fields, such as the torso, arms, and legs. The size of the cortical representation of a body part corresponds with the spatial resolution of touch on that part.
Studies have shown that, within any small region of any of the areas and subareas of the somatosensory cortex, adjacent locations receive tactile signals from adjacent locations on the body surface, forming a somatotopic map on the cortex, but a map that is somewhat disarranged and distorted. It’s disarranged in that larger adjacent regions of the cortex don't necessarily receive signals from adjacent parts of the body—for example, the cortical region that receives signals from the face is adjacent to the region that receives signals from the hand and fingers. And it’s distorted in that relatively more cortical space is devoted to receiving signals from body parts where sensory receptors are densely distributed and have small receptive fields, such as the fingertips and lips, while relatively less space is devoted to body parts with fewer receptors that have larger receptive fields, such as the torso, arms, and legs. The size of the cortical representation of a body part corresponds with the spatial resolution of touch on that part.
12.2 Explain - dnd
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Drag and drop each label into the correct blank box on this illustration of the somatosensory cortex.
12.3 Explain - Custom Activity
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Signals from somatosensory receptors in each part of the body travel to a specific portion of the somatosensory cortex (area S1). Stimulating the body part results in neural activity in that portion of the cortex and in the perception of the stimulation. In fact, stimulating that portion of the cortex with an electrode would produce the same perception of a sensation in that part of the body, without any actual stimulation of the body. This mapping of body parts onto portions of the cortex defines a somatotopic cortical map. Each subarea of S1 contains essentially the same map.
Click on any part of the body or any portion of the somatosensory cortex to reveal the somatotopic map. Only the left somatosensory cortex is depicted here, which would represent only the right side of the body. But for illustrative purposes, both sides of the body are included.
12.4 Explain
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What Are Somatotopic Cortical Maps?
The somatosensory cortex is located in the postcentral gyrus, a strip at the anterior (front) of the parietal lobe, just behind the central sulcus. It consists of two main subregions—the primary somatosensory cortex (or S1) and the secondary somatosensory cortex (or S2). S1 is itself divided into four side-by-side strips—known as areas 3a, 3b, 1, and 2.
Studies have shown that, within any small region of any of the areas and subareas of the somatosensory cortex, adjacent locations receive tactile signals from adjacent locations on the body surface, forming a somatotopic map on the cortex, but a map that is somewhat disarranged and distorted. It’s disarranged in that larger adjacent regions of the cortex don't necessarily receive signals from adjacent parts of the body—for example, the cortical region that receives signals from the face is adjacent to the region that receives signals from the hand and fingers. And it’s distorted in that relatively more cortical space is devoted to receiving signals from body parts where sensory receptors are densely distributed and have small receptive fields, such as the fingertips and lips, while relatively less space is devoted to body parts with fewer receptors that have larger receptive fields, such as the torso, arms, and legs. The size of the cortical representation of a body part corresponds with the spatial resolution of touch on that part.
Studies have shown that, within any small region of any of the areas and subareas of the somatosensory cortex, adjacent locations receive tactile signals from adjacent locations on the body surface, forming a somatotopic map on the cortex, but a map that is somewhat disarranged and distorted. It’s disarranged in that larger adjacent regions of the cortex don't necessarily receive signals from adjacent parts of the body—for example, the cortical region that receives signals from the face is adjacent to the region that receives signals from the hand and fingers. And it’s distorted in that relatively more cortical space is devoted to receiving signals from body parts where sensory receptors are densely distributed and have small receptive fields, such as the fingertips and lips, while relatively less space is devoted to body parts with fewer receptors that have larger receptive fields, such as the torso, arms, and legs. The size of the cortical representation of a body part corresponds with the spatial resolution of touch on that part.
12.5 Test - single choice
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Correct! Click EXPLAIN if you want to review this topic.
Incorrect. The correct answer is С. Click EXPLAIN if you want to review this topic.
12.6 Test - single choice
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Correct! Click EXPLAIN if you want to review this topic.
Incorrect. The correct answer is D. Click EXPLAIN if you want to review this topic.
12.7 Test - single choice
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Correct! Click EXPLAIN if you want to review this topic.
Incorrect. The correct answer is D. Click EXPLAIN if you want to review this topic.