BME251_Fall2011_HW3

BME251_Fall2011_HW3 - BME 251 Systems Physiology 1 Homework...

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BME 251 Systems Physiology 1 Homework 3 – due in clas s Thursday, September 15, 2011 at 11:00 am Please work with each other to improve your understanding of and ability to communicate about the material. What you turn in must, however, reflect your individual understanding and your unique communication style. Copying another person's answer, with or without his/her permission, or copying a group answer is not allowed and will be considered an Honor Code violation. Submissions will be screened for similarities with papers from other students in the class. Be sure to cite all references that you use. Write and sign the honor pledge at the end of your assignment – “I pledge on my honor that I have neither given nor received unauthorized aid on this assignment.” E 1. Model the electrical properties of axon. You will begin by completing the diagram above to model a single region of excitable tissue. Note that the extracellular fluid is indicated in the diagram as the terminal marked “E” and the intracellular fluid is indicated as the terminal marked “I.” a. Note that there are branches in the circuit corresponding to potassium, sodium, and chloride ions. To each branch, add the circuit symbol for a battery. b. Explain why you oriented the positively and negatively charged terminals of the batteries in the manner that you did. Page 80 – Nernst potential A positively charged ion moving in the direction of +X carries a positive current. Direction of current expressed as direction positive charges are moving – Na goes into cell, K out both the concentration and electrical gradients for Na favor its movement into the cell c. What is the potential difference between points I and E? (In words or symbols; don’t try to compute the actual potential).
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d. Note that the sodium and potassium conductances are indicated as variable conductors. However, these conductances can be considered to be composed of two distinct portions: a constant conductance (the resting, or “leak,” conductance) and a variable conductance. Redraw the diagram such that these two conductances for each ion are indicated separately. e. What biological structures do the leak and variable conductances represent?
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BME251_Fall2011_HW3 - BME 251 Systems Physiology 1 Homework...

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