zoo_523_probset10

zoo_523_probset10 - Problem Set 10 1. Most cells in the...

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Problem Set 10 1. Most cells in the retina show what is called a “graded response”. What does this mean? This means that these neurons do not produce action potentials in response to stimuli. Rather, the amplitude of their response depends upon the amplitude of the stimulus. 2. Outline the series of events that leads from the surround cone photoreceptors to a “Surround- OFF” response in a ganglion cell. Describe each synaptic connection, and the resultant hyper- or depolarization of the postsynaptic cell. A diagram is fine. Cone photoreceptors are the color photoreceptors, which have the highest concentration at the fovea. Light hits the photoreceptors and changes the shape of the pigment, photopsin. This leads to a second messenger cascade, reduction in cGMP, and closing of sodium channels, which hyperpolarizes the cell. Approximately one to twenty cones synapse (converge) on one bipolar cell, and this varies by eye region. Photoreceptors release glutamate when they do not sense light. Some bipolar cells will be excited by this glutamate, sodium channels will open, and the bipolar cell is activated in response to dark. Other bipolar cells will be inhibited by glutamate, sodium channels will close, and they become hyperpolarized – these cells in effect depolarize when light is present in their receptive field. This explains the “center” response.
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zoo_523_probset10 - Problem Set 10 1. Most cells in the...

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