Bio 35400 Homework 2 (due 2/13) Instructions: This assignment has a total value
ID: 3509409 • Letter: B
Question
Bio 35400 Homework 2 (due 2/13) Instructions: This assignment has a total value of 20 points. Some questions require the use of a calculator. Write or type out your answers on a separate sheet of paper, clearly label your final answer and the question that it goes with. You do not need to explain your answers unless the question asks for an explanation. For questions involving math, showing your work may allow you to get partial credit even if your final answer is wrong. You may work with other students in the class as long as you work together and no one is simply copying someone else's answers Question 1. You want to study the passive electrical properties of an axon from a newly characterized type of neuron. You inject current to induce a 10 mV depolarization at one end of the axon, and you measure the resulting depolarization at different points along the axon. Shown here is the trace of measured depolarization along the axon as a function of distance from the current injection 10.0 9.0 8.0 7.0 4.0 1.0 a. (1 pt) What is the approximate value of the length constant? 0.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Distance (mm) b. (1 pt) What is the approximate value of the depolarization at a distance of two length constants from the location of applied voltage? Question 2. (2 pts) You have constructed a model system to study ionic permeability consisting of two compartments separated by a lipid bilayer. The bilayer contains K' channels and Na channels. The ionic concentrations in the right and left compartments are K": left = 400 mM, right = 10 mM Na": left = 50 mM, right = 460 mM At room temperature, what are the equilibrium potentials for K and Na* in this system? Express each membrane potential as referring to the charge of the left compartment relative to the right (e.g. a positive membrane potential means that the left compartment is more positive than the right compartment) Question 3. You are studying the electrical properties of a neuron in a dish. The extracellular solution bathing the cell contains 145 mM Na* and 5.6 mM K'. You determine that under these conditions, the Na* equilibrium potential is +35 mV and the K equilibrium potential is -60 mV All measurements are conducted at room temperature a. (2 pts) What are the intracellular Na and K concentrations? b. (2 pts) If you held the neuron at +20 mV, in which direction would the net flow of each ion be? c. (2 pts) If you held the neuron at +50 mV, in which direction would the net flow of each ion be?Explanation / Answer
1. a) Length constant () corresponds to the distance where a graded potential has decreased to 37% of its original amplitude.
Length constant = 1 mm (the amplitude decreases from 10 mV to 3.7 mV)
b) The aapproximate value of the depolarization at a distance of two length constants from the location of applied voltage is 1.5 mV.
2.
Equilibrium potential for K+ = - 61.5 log [Ko] / [Ki]
= - 60 log 40
= - 60 X 1.60 = - 96 mV
Equilibrium potential for Na+ = 60 log [Nao] / [Nai]
= 57.6 mV
3.
a. Equilibrium potential for K+ = - 60 log [Ko] / [Ki]
-60 = -60 log 5.6/ [Ki]
Intracellular concentration of K = [Ki] = 0.56 mM
Equilibrium potential for Na+ = 60 log [Nao] / [Nai]
+35 = 60 log 145/[Nai]
Intracellular concentration of Na = [Nai] = 37.87 mM
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.