Week1-L2-membrane and action potential Flashcards
flux of ions
n0 of molecules crossing a unit area per unit time
diffusion
useful over short distances down conc. gradient till dynamic equilibrium
charged molecules proterties
unlike attract and like repel
voltage
provide energy to move ions
current
movement of charged ions due to potential difference
resistance
barrier to movement of ions
membrane potential measurements
outside electrode called zero-volt level and inside cell electrode which measure the pd the (negative to outside)
ions channels
selective changed of permeability to specific ions and depending on the transmembrane voltage, ligands, and mechanical forces
membrane potential if no gradient of charge separation
0
membrane potential if ion channels present
increase separation of charge until electrochemical equilibrium is reached
electrochemical equilibrium aka the equilibrium potential
electrical forces balance the diffusion forces
how to calculate the equilibrium potential
Nernst equation
mM of sodium at resting potential
intra-10
extra-150
mM of potassium at resting potential
intra-150
extra-5
Ek means
equilibrium potential of potassium
Ek value
-90mV
ENa value
+72mV
Em value
-70
why membrane potential not at Ek or ENa
membrane has a mix of both K and Na equilibrium across membrane but K»> Na, more towards K potential
Goldman-Hodgkin-Katz(GHK) equation
accounts for the relative permeability of ions at one time when calculating the real membrane potential
GHK scale for P value-ion channel
0-1 where 0 is closed and 1 is opened
depolarisation
Em towards 0mV
repolarisation
Em decreases towards resting potential
overshoot
Em increase from 0 to more positive
hyperpolarisation
Em decrease beyond resting potential
graded potential along axon
decay: leakage as impulse propagates
graded potential characteristics
change in Em in response to stimulation
occur at synapse and sensory receptors, initiate or prevent ap
absolute refractory period mechanism
occurs during the repolarisation period
activation gate open as K+ leaves the cell and inactivation gate close by part of protein plugging the pore.
new action potential cannot be triggered even by strong stimulus
relative refractory period mechanism
occurs during the hyper polarisation period where a stronger sitmulsus can trigger an action potential
