Transcript Membrane Potential - Univerzita Karlova v Praze

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
Phospholipid bilayer
Proteins
peripheral
integral
non penetrating
penetrating (transmembrane)
Na+- K+ pump
+
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+
Na+
K+
A-
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 C1to
concentration C2
 Ao= R.T.ln [C1] /[C2 ]
 Electric work
 The work, which must be done to move 1 mol of
the substance across the potential difference E
 Ae = E. n. F
 R.T.ln [C1] /[C2 ] = E. n. F
 E=
How to calculate the magnitude
of the membrane potential




Ao= Ae
R.T.ln [C1] /[C2 ] = 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