Lesson 1
Electricity is fundamental method which neurons communicate one another
Neuron “at rest“ = neuron not currently involved active electrical signalling
Resting potential = voltage diference across membrane of resting neuron
History of bioelectricity
Luigi Galvani
Physician, physicist, philosopher
18th century in Bologna, Italy
1771, disect frog when metal scalpel touch nerve in frog cause frog leg move
Though discovered key to life
Inherent electricity in animal which lead to movement
Posited existance of animal electric fluid
Live on in many modern term
Galvanic
Galvanometer
Alessandro Volta
Physicist and contemporary of Luigi Galvani
Repeat Luigi Galvani but doubt existance electric fluid
Eventually developed first battery
Prove similar electricity can generate outside living creature
Coined term
Galvanism = refer electrical phenomena in living creature
Luigi Galvani and Alessandro Volta ignited study of electrochemisty and bioelectricity
Voltage
Voltage = difference in electrical potential between two points
Electrical potential = help describe strength and direction of force motivate electrical charge flow
Based on electrostatic force between charge object
Ions move according to potential
Electrostatic force = describe attraction/repulsion between charged particles (ions)
Opposite charge attract
Like charge repel
Voltage = tell strength of potential difference
Measured in volts (V)
Neuroscience, relevent point inside and outside cell
Seperated by membrane which imperable charged particle
Ion need help channel or pump to flow through
Ion move through membran channel cause charge difference between two compartment
Result potential/voltage acriss membrane
Membrane allow voltage to be maintained
Introducing resting potential
Neuron send signal use electricity
Neuron are electrically charged
Lipid memebrane of neuron seperate solutions of charge particles
Seperation create difference in potential energy across lipid membrane
Typical neuron parts
Soma/cell body
Axon
Dendrite
Outer surface all neuron part is made up bilayer of lipid molecule
Is partitioned from inside to outside cell
Called cell membrane
When neuron at rest not electrically neutral
Membrane potential = difference of electrical potential energy inside and outside living neuron
Eg
Potential energy/stored energy
Battery generate electrical potential between positive and negative terminal
When wire connect positive and negative terminals electrical potential cause electron flow negative to positve
Potential difference inside and outside resting neuron = negative 70 millivolts (mV)
Voltage is relative quantity
Only really meaningful talk voltage between two point
Must define what point call zero
Conventionally consider outside cell to be zero
Electrical nomenclature called ground
Inside and outside of neuron made of water and host of stuff (protein, ion, sugar)
Charged ion, sodium, potassium, calcium, chloride are present reasonably high concentrations
Membrane potential vs resting potential
Membrane potential (Em)
General term describe voltage across membrane
Membrane potential of neuron can vary
Eg
Frin -90mV to +60mV
Resting potential
Membrane potential of neuron at rest
Meaning not sending or receiving signals
Generally between -60mV and -70mV
Diffusion and electrostatistics
Inside and outside neuron, ions and other particles exist in aqueous solution and able move around
Forces that guide movement of ions and other particles
Diffusive force
Process which particles spread out/mix
Movement is governed by thermal movement of individual molecules
Process cause particles move from region of high concentration to low concentration
In essence is inexorable force drive particle down concentration gradient from high to low
Electrostatic force
Particles can have charge
Positive or negative
Particle charge serve as basis of electricity
Opposite charges attract
Like charges repel
Movement of K+ and Na+ ion can change membrane potential
Potentials and equilibrium
Ion movement through membrane channel guided by diffusive and electrostatic force
Movement of ions can change membrane potential
Most cell in human body have membrane potential ranging -5mV to -100mV
Each side of membrane is electroneutral
Electroneutral = no net charge on each side
Since for bulk solution every positive charge there is negative charge to balance out
Membrane potential come from tiny imbalance that accumulate very close to membrane
Charge imbalance generates electric field across membrane
Result in electrical potential
If concentration of ion mM is different, membrane is impermeable, there is appropriate number matching oposite charge ion, Em of situation is 0mV
If concentration of ion mM is different, channel for ion, there is appropriate number matching opposite charge ion, greater concentration ion will move to lower concentration
Result in different charge inside and outside as there is appropriate number matching opposite charge ion
Extra charges will line up to membrane (both inside and outside)
But concentration still greater inside as charged ions
Have to think about electrostatic force
When move ion down concentration gradient inside to outside additional new charge create electrostatic force repels like charges from diffusing
Moving 1 in 100,000 ion accross membrane is sufficient create negative 80 millivolt membrane potential
Electrostatic force move tiny fraction charged particle other side membrane enough balance out diffusion of large number particles
Electrostatic force much stronger compared diffussion
So few ion move across membrane to generate membrane potential so concentration inside and outside unchanged
Concentration gradient determine equilibrium potential
Nernst equation
Used calculate potential across membrane given concentrations particular ion inside and outside cell