BearCh10-ARCQedt - Chapter 10 The Central Visual System...

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Chapter 10 – The Central Visual System Answers to Chapter Review Questions Page 1 of 5 Copyright © 2007. Lippincott Williams & Wilkins. Ancillary material to accompany Bear et al.: Neuroscience: Exploring the Brain, 3e Question 1: Following a bicycle accident, you are disturbed to find that you are unable to see anything in the left visual field. Where has the retinofugal pathway been damaged? Answer: Lesions anywhere in the retinofugal projection from the eye to the lateral geniculate nucleus (LGN) to the visual cortex may cause specific visual deficits depending on the site of the lesion. The bicycle accident has resulted in a transection of the right optic tract , resulting in blindness in the left visual field as viewed through either eye. Axons from the nasal retina of the left eye and temporal retinal of the right eye have been damaged. In contrast, a transaction of the right optic nerve would render a person blind in the right eye because both nasal and temporal axons originating from the right eye would be damaged; none of the axons in the optic nerve have crossed to the opposite side of the brain. Crossing, or decussation, occurs at the optic chiasm, which lies between the optic nerve and the optic tract. Question 2: What part of the visual field is represented in the left LGN? Answer: The left LGN receives retinal information about the right visual field. Left LGN neurons receive synaptic input from the retinal ganglion cells in the nasal half of the right retina and the temporal half of the left retina. In the left LGN, the left eye (ipsilateral) axons synapse on cells in layers 2, 3, and 5 and the right (contralateral) eye axons synapse on cells in layers 1, 4, and 6. Question 3: A worm has eaten part of one lateral geniculate nucleus. You can no longer perceive color in the right visual field of the right eye. What layer(s) of which LGN is damaged? Answer: The worm has eaten koniocellular neurons in the left LGN, and perhaps some parvocellular neurons receiving contralateral retinal projections. In addition to neurons in the
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Chapter 10 – The Central Visual System Answers to Chapter Review Questions Page 2 of 5 Copyright © 2007. Lippincott Williams & Wilkins. Ancillary material to accompany Bear et al.: Neuroscience: Exploring the Brain, 3e six principal layers of the LGN (layers 1–6), there are numerous tiny neurons on the ventral
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BearCh10-ARCQedt - Chapter 10 The Central Visual System...

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