Prob Set 7 Q&A

Prob Set 7 Q&A - Problem Set 7 Cellular...

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1 Problem Set 7 Cellular Neurobiology Fall 2010 1. How does the presence of limbs affect the embryonic development of motor neuron populations? Describe an experiment that revealed this result. In developing nervous systems, the embryo produces around three times more neurons than necessary and eventually trims down the excess neurons based on the size of the target and the amount of neurotrophic factor it secretes. The neurotrophic hypothesis suggests that the target muscles only provide enough neurotrophic factor for a fraction of the total number of motor neurons. The survival of the motor neurons depends upon their synapsing with a muscle and receiving these growth factors so they can survive. In this way, the muscles can dictate the size of the neuronal population innervating them. The experiment discussed in class used chick embryos and showed that by adding or removing limbs during embryonic development, one could control the number of surviving motor neurons. More limb = more neurotrophin = more neurons and visa versa. 2. Describe the experiment Roger Sperry performed that allowed him to arrive at the Chemoaffinity Hypothesis. How did the results of this experiment support his theory? Frog retinal ganglion cell axons are able to regenerate when severed. Roger Sperry used this property to his advantage by cutting the optic nerves that connect the retina of a frog to the tectum, rotating the eye 180 degrees and observing how the axons regenerate. He noticed that the retinal axons reestablished the original pattern of connections in the
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Prob Set 7 Q&A - Problem Set 7 Cellular...

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