Study Qs - physiology_key

Study Qs - physiology_key - 1. Poor Dr. Westwood took a...

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1. Poor Dr. Westwood took a vacation in Australia to recuperate from his experiences with the pufferfish and the pitohui. While snorkeling near the Great Barrier Reef, he began to feel an uncomfortable numbness and paralysis. It’s possible that he was stung by a cone snail and injected with Conotoxin, which blocks voltage-gated calcium channels. Describe one way in which this toxin could cause Dr. Westwood’s paralysis. VG Ca channels in neurons allow for a rise in intracellular Ca that is responsible for initiating neurotransmitter release in response to an action potential. Failure to release transmitter by a motor neuron would prevent activation of a muscle. or VG Ca channels in muscles trigger the rise in intracellular Ca that activates myosin activity and therefore muscle contraction in response to a neuronal signal. NB: This is technically only correct for skeletal and cardiac muscle. And in skeletal muscle the VG Ca channel don’t actually produce an inflow of Ca into the muscle cell. Still, they have to open in order to trigger the opening of channels inside the cell that release stored Ca from the ER (SR) 2. The figure below shows an experimental setup with two neurons and a muscle cell. You have inserted a stimulating electrode with which you can depolarize neuron 1. You also have inserted 3 voltage recording electrodes with which you can measure membrane potential in the first neuron (electrode A), in the second neuron (electrode B) and in the muscle cell itself (electrode C). Under control conditions a stimulation causes the muscle cell to contract. For each of the conditions listed below, indicate what you would expect to see. A. (6pts) If you introduced either tetrodotoxin and omega -conotoxin (a voltage-gated calcium channel inhibitor), would you see (answer yes/no) : Tetrodotoxin omega -conotoxin depolarization at electrode A? N Y depolarization at electrode B? N N muscle cell contraction? N N B. (4pts) In another setup with two different neurons, you find that you don’t get muscle contraction when you stimulate neuron 1, even in the absence of toxins. However, if you stimulate neuron 2 on a dendrite you do see contraction. If you stimulate both neuron 1 and 2 you see no (or very few) contractions. How can you explain these results? In this setup neuron 1 must release an inhibitory neurotransmitter, causing neuron 2 to hyperpolarize. Stimulation of neuron 1 counteracts the depolarizing stimulus on the dendrite of neuron 2. C. (8pts) You make a mistake when you were setting up for the first experiment and you bathe the cells above in a solution with ten times the normal concentration of K + ions. In
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the absence of any stimulation or toxins what, if any, effect would you expect to see in the recording electrode C? What, if any, effect on contraction would you expect to see? Briefly explain your predictions.
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Study Qs - physiology_key - 1. Poor Dr. Westwood took a...

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