Physiology Homework [Due in 1.5 hours]

You should complete these questions ON YOUR OWN.  Please turn in the answers to these questions at the start of your next laboratory session. You should provide citations for any sources used to answer these questions. Remember to use credible sources (Access Medicine and/or Medline).


 Part I


  1. (a) If each individual action potential is the same magnitude (all or none), how do neurons transmit information about the strength of a stimulus? (b) How do neurons transmit information about the duration of a stimulus?  (2 pts)

  2. What is the physiological reason that action potentials can only be propagated in one direction in a neuron (from cell body towards the synaptic terminal and not vice versa)? Fully explain. (2 pts)

  3. If you put ouabain, an inhibitor of the Na+/K+ pump, on a neuron and then stimulate the neuron repeatedly, what do you think will happen to the action potentials generated by that neuron? Briefly explain your answer. (1 pt)


  4. A synapse is bathed in a Ca2+ free solution, a solution that is otherwise identical to extracellular fluid in regards to ionic composition. An action potential is then produced in the pre-synaptic neuron and the action potential travels down the axon to the synapse. However, in this Ca2+ free solution, the usual response of the post-synaptic cell did not occur. What is the reason for the lack of response in the post-synaptic cell? (1 pt)



    Answer to Part 1 is $8


    Answer to part 2 is $7


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     Part II

    1. (a) What happens to the myelin in people who suffer from multiple sclerosis (MS)?  You should then explain the reason for Phyllis’ symptoms that were presented in parts I and II of the case.  (b) Why is there an elevated level of myelin basic protein in Phyllis’ cerebrospinal fluid? (1 pt)

    2. (a) What is an evoked potential test and how it is used to diagnose MS? (b) What would be the effect on action potential conduction at a region of axon where the disease was having its effect? (1 pt)

    3. Phyllis has been told that she probably has the relapsing remitting form of MS. During remission, axons affected by the disorder regain their function. If voltage-gated sodium channels are concentrated in certain regions of the myelinated axon prior to the disease, what do you think happens to them after MS has had its effect? (1 pt)

    4. (a) How could treatment with interferon beta help control Phyllis’ symptoms? (b) How could treatment with corticosteroid help control Phyllis’ symptoms? (1 pt)




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