Resting potential

Question 1

What is flux?

Answer 1

rate of transfer of molecules

dynamic equilibrium = no net flux

Question 2

What is current?

Answer 2

movement of ions due to potential difference

amps

Question 3

What is resistance?

Answer 3

barrier that prevents movement of ions

ohms

Question 4

What is RMP of a nerve cell?

Answer 4

-70mV
inside negative compared to outside
reference electrode on outside of axon and intracellular axon to measure potential difference between the two

Question 5

How is RMP produced ?

Answer 5

motor neurones membranes only selective for K at rest

electrical and chemical gradients balance to achieve stable membrane potential of -70mV

Question 6

What is state of electrochemical equilibrium?

Answer 6

electrical forces balance [] gradient/chemical forces to achieve a stable trans-membrane potential

electrochemical equilibrium when electrical force prevents further diffusion across the membrane

Question 7

What is equilibrium potential?

Answer 7

potential at which electrochemical equilibrium has been reached - prevents diffusion of ions down [] gradient

Question 8

How can EP be calculated?

Answer 8

Nernst equation (inside/outside)
Na out(15) in(10)
K out(5) in(150)

Question 9

Why is membrane potential not EK = -90mV?

Answer 9

ENa = +73mV

membranes have a mixed permeability to Na, Cl and K but at rest permeability to K much greater than to Cl/Na

Use GHK equation

Question 10

What does the GHK equation tell you?

Answer 10

describes resting membrane potential with each size of each ion’s contribution proportional to how permeable the membrane is to the ion

P = permeability
= 1 (100% open)
= 0 (100% closed)

Question 11

How are signals propagated along nerve cell?

Answer 11

change in membrane potential along cell markedly/small increments

Question 12

What are graded potentials?

Answer 12

nerve cells can signal by graded depolarisations or hyperpolarisations

these are small changes in membrane potential proportional to the size of the stimulus, vary in size
as current moves down axon charge dissipates across cell membrane
- typically at synapse (summation possible, cancel out)
- touch receptors
- contribute to initiating/preventing AP

action potentials are all or nothing

Question 13

What do graded potentials allow?

Answer 13

integration

AP does not automatically produce AP in adjacent cell

AP creates graded potential on adjacent cell that must surpass threshold in order to propagate signal

graded response at synapse/receptor allow integration of inhibitory and excitatory response
NOT ALL OR NOTHING