equations/maths to remember

nernst equation

Eion = 61.5/z x ln( [ion]out/[ion]in )

driving force

emf = Vm - Eion

if emf is positive

• cation efflux / anion influx

• depolarisation

if emf is negative

• cation influx / anion efflux

• hyperpolarisation

time constant definition

• time taken to reach change in voltage 63%

• how quickly a membrane reaches a new voltage after current is injected

  • temporal summation

time constant equations

• t = capacitance / conductance

• t = resistance x capacitance

if capacitance increases what happens to time constant

• time constant increases

• greater charge held so takes longer

if conductance increases what happens to time constant

• time constant decreases

• membrane is more permeable to ions so it takes less time to reach change = 63%

length constant definition

• the distance at which the voltage has depleted to 37% of its original value

• sqaure root of membrane resistance / auxonial resistance

capacitance equation

charge/voltage

conductance equation

• G = I/V

• V may be the driving force

maximum volume attained after superfusion

• V2 = V1xP1/P2

how to work out maximum volume with osmotically inactive and active compartments

• osmatically inactive + omsatically active times by initial volume / superfused volume

electrical charge stored in current step

triangle Q = C x change in voltage

number of monovalent ions responsible for charge storage

total membrane charge / charge on a single monovalent ion