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Bio 222 Exam 3
Lec 12 - Somatosensory system 1 Touch
8
Biology
Undergraduate 4
11/15/2010

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Term
mechanoreceptors
Definition
-receptors: skin (a-beta fibers)
-cell bodies: dorsal root ganglion
-primary afferent axons (skin) to spinal nerves to spinal cord
-primary afferent axons ascend the spinal cord via ipsilateral dorsal columns (white matter)
Term
pacinian corpuscle (largest)
Definition
-10-15% of hand mechanoreceptors
-sensitive to high frequency vibration
-low spatial acuit (10+mm)
-"onion-like"
Term
ruffini's endings (second largest)
Definition
-20% of hand mechanoreceptors
-sensitive to skin stretch
-low spatial acuity (7mm)
Term
Meissner's corpuscle (1/10th of pacinian)
Definition
-40% of hand mechanoreceptors
-sensitive to low frequency vibration
-intermediate spatial acuity (3mm)
Term
merkel's disk (smallest)
Definition
-25% of hand mechanoreceptors, especially fingertips
-sensitive to edges, points, curvature
-high spatial acuity (0.5mm)
Term
Structure of specialized endings
contribute to receptor function (e.g. pacinian corpuscle)
Definition
onion-like capsule confers sensitivity to high frequency vibrating stimuli but not steady pressure
Term
dermatome
Definition
-skin innervated by right and left dorsal roots for a single spinal segment
-numbered by spinal seg providing innervation
-overlap (cutting one doesn't lead to loss of all sensation)
Term
topographic organization of dorsal columns
Definition
lower body axons in gracile tract (medial)
upper body axons in cuneate tract (lateral)
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