#Ammendment E = σ / Ɛ not E = σ / 2Ɛ

Problem 4

Nerve Cells

Group Number:
2

Members:
Eugene Clifford

Sian Sweeney

Matthew Kinsella

Akin Goktas
Introduction:
In this report the mechanics and electrical theories of Nerve cells will be discussed. We will explore the way Nerve cells create and transmit electrical impulses and how a nerve cell membrane can be compared to a parallel plate capacitor. Topics such as Dielectrics, Capacitance and Permittivity will also be approached. In this problem we need to find the Electric Field intensity (E) within the membrane using surface charge density (σ). Find voltage (V) using E and the distance from plate to plate (d). Plot the relationship between σ and V on a graph and thus calculate Current (I) using this information and the area (A). For the purpose of this report the membrane faces will be referred to as “plate A” and “plate B”.

Theory:
A nerve cell membrane acts like a dielectric parallel plate capacitor, as it is water filled (dielectric material) and has two membrane faces (plate A & B). As seen in Figure 1 below.
[pic]
Figure 1: A dielectric parallel plate capacitor. [1]

We portray charge lining up on the outer side of each face of the membrane just as on the plates of a capacitor [2]. As external forces cause the nerve cells to electrically transmit their messages, it is safe to assume that the impulses are triggered by a change in charge density, polarity, field intensity and /or other similar factors. In this problem it is a change in charge density that we are looking at. This is what creates the transmitted current within the membrane. A nerve fiber starts with the cell body. Dendrites stretch out from the cell body in much larger numbers than shown in Figure 2 below. Dendrites are narrow tubes composed of the cell’s membrane. These are the areas