Bioelectricity

Biophysics, lecture 3

electric change

a property of subatomic particle, which determines its behaviour in the electromagnetic field

static electricity

build up of electric charge on the surface of objects

current

the flow of electric charge along electrical conductor as a consequence of electrostatic discharge

Coulomb’s law

describes the magnitude of the electrostatic force between two electric charges

Coulomb’s law applies only

to the magnitude of the force, irrelevant to the charge

Electric field

Michael Faraday, surrounds electrically charged particles and time-varying magnetic fields

electromagnetic field

property of space caused by the motion of an electric charge

Kirchhoff’s circuit laws

current law, voltage law, electromotive force

current law

sum of current entering the electrical junction equals the sum of current exciting it

voltage law

sum of voltage in a simple enclosed circuit equals zero; electric cell gives the charge an electromotive force, and then the electric resistance dissipates this force

electromotive force

force applied to the charge derived from the electric potential difference applied to the circuit

ohm’s law

current passing through a conductor between two points is directly proportional to the potential difference across this two points

ohm

unit of resistivity, resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces in the conductor a current of 1 ampere

strong conductors

small charged ions i.e. inorganic salts

weak conductors

large charged particles i.e. organic acids, peptides, etc.

capacitor

device for storing electrical energy

Leyden jar

originally, the amount of capacitance was measured in number of jars of a given size

anode

electrode attractive for negative ions (anions)

cathode

electrode attractive for positive ions

charged particles

subatomic particle or ions

plasma

group of charged particles

Nernst equation

can be used to determine the equilibrium reduction potential of a half cell in an electrochemical cell

Nernst potential

physiological application of Nernst equation; potential of an ion of charge across a biological membrane, the reversal potential

reversal potential of an ion

Membrane potential at which there is no net flow of that particular ion from one side of the membrane to the other. APPLIES ONLY TO THE STATIC SITUATIONS

Goldman equation

To overcome limitations of Nernst equation in cell membrane physiology, it is used to determine the reversal equilibrium potential across a cell’s membrane, taking into account all of the ions that permeate through that membrane

equilibrium potential

the state in which the tendency of ions (electrically charged particles) to flow across a cell membrane from regions of high concentration is exactly balanced by the opposing potential difference (electric charge) across the membrane

driving force

refers to the difference between the actual membrane potential and an ion’s equilibrium potential

ionic current

is equal to the ion’s conductance multiplied by the driving force, the difference between the membrane potential and the ion’s equilibrium potential. Is 0 if the membrane is impermeable to the ion regardless of the size of the driving force

cathode potential

closing potential

anode potential

opening potential

bioelectricity

electric, magnetic or electromagnetic fields produced by living cells, tissues or organisms

bodily conductors

neurons (na+,k+,cl-), skeletal and cardiac muscles (ca2+), smooth muscles (Ca2+)

ampullae of Lorenzini

sharks detect electric fields in the water (difference between the voltage at the skin pore and the voltage at the base of the electroreceptor cell)

depolarisation of the cell

change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside.

electricity as a weapon

specially modified muscle cells stacked in functional groups (Volta’s voltaic piles) joined in serial or parallel circuits

electrical animals

talkative aba, shocking eel (500-1000V, 16-20A), deadly torpedo (200V, 50A)

electrocardiogram

transthoracic interpretation of the electrical activity of the heart over time acquired from electrodes attached to the skin

electroencephalogram

record of electrical activity of brain recorded by 8-16 pairs of electrodes attached to scalp

electrocyte

A modified striated muscle cell that does not contract, but produces electric signals

electrophoresis

laboratory technique used to separate DNA, RNA or protein molecules based on their size and electrical charge