Reference no: EM132773677

Question 1: Three students are given the experimental setup shown in Figure 16. It consists of 4 electrodes that surround the axon of a giant squid neuron. The students are given two current sources to power the two pairs of electrodes and told to use the same current in both power supplies. Therefore, two electrodes will have a current of +10 and the other two a current of -la. The latter are highlighted in red in the figures. Students are asked to trigger an action potential in the neuron. Unfortunately, the instructions they are given do not specify how to connect the power supplies. Student A decides to connect the power supplies so that the current in the electrodes is as shown in Figure 16A. student B decides to connect the power supplies in such a way that the current in the electrodes is as shown in Figure 16$, and student C decides to connect the power supplies in such a way that the current in the electrodes is as shown in Figure 16C.

a) What is the potential along the axon of the neuron as a function of r, i.e. the distance from the origin, for the three cases? Give your answer as a function of the current 10 and the medium conductivity cr.

b) Which of the three students has a better chance of triggering an action potential? Justify your answer

c) Plot the electric potential along the axon as a function of r and estimate graphically, where the action potential will be triggered. Justify your answer. guess work will not attract marks.

Question 2: Let's consider a cylindrical fibre in an infinite medium of conductivity cr=0.2 Sim. An action potential propagates along the fibre and the tip of a sensing probe placed at a distance of 1mm from the fibre (see Figure Q14) is used to record the electrical activity on the fibre. The reference electrode (not shown in the figure) is placed at a large distance from the fibre and can therefore be assumed to be placed at infinity. As the action potential propagates, it causes a depolarization wave that travels down the fibre. From the extracellular medium perspective. the transmembrane currents at the front of the depolarization wave are equivalent to those of a dipole as shown in Figure Q14. oscilloscope

Figure Q14

Answer the following questions assuming that the fibre is much smaller than the distances considered in the problem and that the probe is small enough as not to perturb the induced electric fields.
a) At time t=0. the depolarization wave is at location zo=1mm. as shown in
Figure Q14. At this moment the source +lc, and of the equivalent dipole
are at location z=0.9mm and z=1.1mm. respectively. What will be the voltage recorded by the probe if l3=1.2mA?
b) Draw a qualitative plot of the voltage measured by the probe as a function of the position of the action potential as it travels down the fibre. Hint You may want to consider what the voltage would be when the front of the depolarization wave is at various Z values (e.g. z 1. 0.5. 0. -0.5 -1 --/).

c) If instead of placing the refence electrode at infinity the reference electrode is placed next to the probe electrode. what would be the voltage difference recorded in the following 3 cases? Draw a qualitative plot of the voltage difference between the two electrodes as a function of the position of the action potential as it travels down the fibre.

i. Case 1: Reference electrode located at x=-1mm. z=Omm
ii. Case 2: Reference electrode located at x=2mm. z=Omm
iii. Case 3: Reference electrode located at x=1 mm. z=1mm

Attachment:- Bio questions.rar