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Chapter 4: Somatic Sensation: Spinal Mechanosensory Systems

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A 25-year-old male was in an automobile accident and suffered a severe spinal cord injury. He had multiple somatic sensory and motor signs. Focusing only on mechanosensation, he had no sense of touch on his right leg and lower chest, to the level of the umbilicus. Which of the following statements best describes the side and level of injury?

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A. Right side of spinal cord at the 10th thoracic segment (T10)

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B. Right, T4

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C. Left, T10

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D. Left, T4

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From which of the listed body regions does the gracile nucleus receive mechanoreceptive input?

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A. Contralateral arm

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B. Contralateral leg

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C. Ipsilateral arm

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D. Ipsilateral leg

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The medial lemniscus—in the medulla, at the level where there is a fourth ventricle—receives its blood supply from which of the following arteries?

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A. Posterior inferior cerebellar artery

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B. Vertebral artery

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C. Posterior spinal artery

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D. Anterior spinal artery

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Comment: At the level of the caudal medulla, where there is little or no inferior olivary nucleus, the anterior spinal artery supplies blood to the medial lemniscus.

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A physician tests vibration sense by touching a tuning fork to the body surface. Which of the following receptors mediates vibration sense?

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A. Thermal receptor

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B. Pacinian corpuscle

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C. Ruffini's corpuscle

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D. Meissner's corpuscle

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Which of the following statements best describes the organization of dermatomes associated with adjacent dorsal roots?

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A. Dermatomes are adjacent, with minimal overlap, so that loss of one dorsal root gives rise to a loss of somatic sensation within the dermatome boundary, as shown in the dermatome maps.

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B. Dermatomes overlap partially, but loss of one dorsal root does not give rise to a noticeable loss of sensation.

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C. Dermatomes overlap partially, so that loss of one dorsal root typically gives rise to a noticeable loss of sensation within the dermatomal boundaries.

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D. Dermatomes overlap nearly completely, so ...

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