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Lecture 1

# Physiology 3140A Lecture Notes - Lecture 1: Electric Field, Lipid Bilayer, Potassium Channel

by OC17532

This

**preview**shows page 1. to view the full**4 pages of the document.**INTRODUCTION – ELECTRIC CURRENTS FOR COMMUNICATION

Electric Potential - - the electric potential (electrostatic potential) at a point in space is the electrical

potential energy divided by charge at is associated with the static electric field

- Measured in volts

- electric field exerts a force on charged objects, accelerating them in the direction of the force

- In the same or opposite direction of the electric field

- if the object has a positive charge the force and acceleration will be in the direction of the

field

Electric Current - - the flow of electric charges or the rate of flow of electric charges; in a wire

(conductor) its carried by electrons, in an electrolyte its carried by ions and in plasma its carried by

both ions and electrons

- measured in amperes (charge flowing at one coulomb per second)

Electrical Resistance - - a measure of an objects opposition to a steady electric current; an object of

uniform cross section will have a resistance proportional to its length and inversely proportional to

its cross sectional area (and of course proportional to the resistivity of the material)

- measured in ohms

- resistance is measured as the proportion of voltage to current (R = V/I)

Capacitance - - the ability of a body to hold an electric charge; its also a measure of the amount of

electrical energy stored (or separated) for a given electrical potential

- measured in farads (one coulomb/volt)

Potential (volts) – mV (10-3 V), uV (10-6 V)

Current (amperes) – nA (10-9 A), pA (10-12 A)

Resistance (ohms) - m (10^6), G (10^9)

Conductance (Siemens) – nS (10-9 S), pS (10-12 S)

DIRECTION OF ELECTRIC CURRENT

- the movement of positive charges

- these move from a point of (high) electric potential to low potential

- larger potential (voltage) difference, the larger the current

- current is also dependent on the medium that is carrying the current (ie smaller dismeter

cable offers a higher resistance than a larger diameter cable)

Ball Rolling Down Hill Analogy – this is an analogy for current flowing from high to low potential;

the height is the potential, the speed of the ball reproduces the current and the surface the ball rolls

on is the resistance – here voltage is seen as analogous to pressure and current is analogous to water

flow

OHM’S LAW (applies to electric circuits) - - the current (I) passing through a conductor is directly

proportional to the voltage difference (V) across the conductor and inversely proportional to the

resistance (R) of the conductor

Therefore I = V/R (or V = IR) and in some cases we use G (conductance) to replace resistance: G =

1/R

Therefore ohm’s law can be written I = GV

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