Membrane Potential Transduction of signals at the cellular level Resting Membrane Potential Action Potential

Why do we need to know about RMP and AP?

Transduction of signals at the cellular level EPSP IPSP Initial segment AP Ca2+ influx Neurotransmitter Neurotransmitter releasing

Somatodendritic part – passive conduction of the signal, with decrement

Axon – the signal is carried without decrement

Preliminary knowledge What is necessary to know beforehand

Cell membrane Proteins peripheral integralnon penetrating penetrating (transmembrane) Phospholipid bilayer

Na + - K + pump

Extrude 3 Na + ions Bring in 2 K + ions Unequal distribution of ions Na + and Cl - extracelullary K + a A - intracelullary

Ion channels in the cell membrane §Resting channels - normally open §Gated channels - closed when the membrane is at rest »opening is regulated by »1. Membrane potential (voltage gated) »2. (chemicaly gated) »3. Membrane potential plus ligand binding (Voltage and chemicaly gated) »4. Membrane stretch (mechanicaly gated)

voltage gated sodium channel

Resting membrane potential

Membrane potential is not a potential. It is a difference of two potentials so it is a Voltage, in fact.

The unequal distribution of ions Na +, Cl - are more concentrated outside the cell K +, A - are more concentrated inside the cell

When the membrane would be permeable for K + only §Chemical driving force §outward movement of K + K+K+ A-A- Na + Cl -

When the membrane would be permeable for K + only §More positiv charges are outside §A - can not leave the cell §electrical driving force emerges §inward movement of K +

When the membrane would be permeable for K + only §Chemical driving force §electrical driving force §electrode can record a voltage §=RESTING MEMBRANE POTENTIAL

Equilibrium potential for K + and Na + When the membrane would be permeable for K + only

Ion distribution in the nerve fiber The voltage can be discharged into surroundings

How to calculate the magnitude of the membrane potential §Osmotic work §The work, which must be done to move 1 mol of the substance from concentration C 1 to concentration C 2 §A o = R.T.ln [C 1 ] /[C 2 ] §Electric work §The work, which must be done to move 1 mol of the substance across the potential difference E § A e = E. n. F §R.T.ln [C 1 ] /[C 2 ] = E. n. F §E =

How to calculate the magnitude of the membrane potential §A o = A e §R.T.ln [C 1 ] /[C 2 ] = E. n. F §E = §Nernst equation

Goldman equation

Action potential

Membrane potential Conductance of the membrane for Na + and K +

Time segment when the AP cannot be elicited