Resting potential

Question 1

describe diffusion

Answer 1

over a short distance 
down conc gradient 
in dynamic equilibrium the particles are evenly distributed 
physical event 
no energy 
spontaneous

Question 2

describe flux

Answer 2

the rate of transfer of molecules
the number of molecules that cross a unit area per unit of time per m squared, per second
in dynamic equilibrium - no net flux

Question 3

describe the properties of ions

Answer 3

charged molecules - mainly positive (but Cl- and SO4 2-)
opposite attract
like repel

Question 4

what is voltage

Answer 4

potential difference between 2 points
volts
generated by ions to make a charge gradient

Question 5

what is current

Answer 5

amps

movement of ions to make a current

Question 6

what is resistance

Answer 6

ohms

barrier that prevents the movement of ions

Question 7

how do you measure the membrane potential of cells

Answer 7

electrode placed outside cell - 0V level
electrode in cell - voltage difference that is negative compared to outside
all cells have membrane potential: heart and neuron -70mV
heart maybe -80mV

Question 8

describe ion channels

Answer 8

hydrophobic membrane impermeable to ions
channels (permeable pores) open and close depending on transmembrane V, ligands/mechanical forces
selective to different ions
movement when concentration is different on opposite sides of the membrane
all channels have gating - part of protein structure, ions move when gates open

Question 9

what happens when no ion channels are open

Answer 9

no diffusion
no separation of charge
0v = membrane potential

Question 10

what happens when the membrane is only permeable to K+

Answer 10

K+ cross membrane down conc gradient - diffusion
charge separation between compartments
this continues but some ions get pulled back because compartment is too +ve
electrical forces balance diffusion forces
electrochemical equilibrium
conc gradient = electrical gradient
equilibrium potential

Question 11

what happens when the membrane is permeable to

Na+

Answer 11

Na+ crosses membrane - driven by diffusional flux
charge separation occurs
enough +ve charge accumulates in other compartment to prevent net movement of Na+
electrochemical equilibrium
electrical gradient balance concentration gradient
electrical force prevent net movement of ions

Question 12

how is membrane potential created by diffusion in a cell

Answer 12

all the K+ ion channels are open
there is also a finite number of Na+ channels that are always open - the P.D is therefore more positive than -90mV with only K+ ion channels open - more depolarised

Question 13

what is the equilibrium potential

Answer 13

the potential at which electrochemical equilibrium has been reached
the potential that prevents diffusion of the ion down the conc gradient

Question 14

difference between equilibrium potentials for Na+ and K+

Answer 14

sign different - due to relative concentration of ions in and out of cell

Question 15

what does the Goldman-Hodgkin-Katz equation show

Answer 15

uses relative permeability of membrane at any one time

P = permeability 1=100%, 0=0%, .5=50% etc

Question 16

depolarisation definition

Answer 16

V = -70-0

Question 17

hyperpolarisation definition

Answer 17

V=-70-90

Question 18

overshoot definition

Answer 18

V=0-positive

Question 19

repolarise definition

Answer 19

V=positive - negative

Question 20

what are graded potentials

Answer 20

change in membrane potential in response to stimulus
depolarisation/hyperpolarisation
larger depolarisation
depolarisation dwindles down cell
they can cancel each other/summate
at synapse there are a lit of inputs
graded in terms of time, stimulation or distance

Question 21

describe the decremental spread of graded potentials

Answer 21

charge dissipates as you move down the axon

Question 22

where to graded potentials occur

Answer 22

synapse

sensory neurons

Question 23

function of graded neurons

Answer 23

contributing to initiating/preventing action potentials
only makes AP if over threshold
allow integration of signals

Question 24

composition of fluid compartments

Answer 24

K and Na - neurons

heart Cl and calcium

Question 25

how do you use the Nernst equation

Answer 25

E=(RT/zF)ln(X2/X1)
E = equilibrium potential
R = gas constant
z = charge for ion
F = faraday’s number - charge per mol of ion
T = temperature kelvin - assume 37 celcius
convert natural log to common log
make compartment 2 outside the cell and compartment 1 inside the cell
E = (-61/z)log(Xinside/Xoutside)

Question 26

recall the typical values for the concentration of potassium and sodium ions inside and outside a neuron

Answer 26

Na inside - 10mM
Na outside - 150mM
K inside - 150mM
K outside - 5mM