Equilibrium potential
Nerst eqn: E=60logCo/Ci (mV)
Eq.pot. for a particular ion, [ion] out/in, 60: constant taking into account: R, T, valance of ion, Faraday elec. constant
If [ ] changes =>E changes
E for K+ ~-80mV, Na+ ~ +60mV
Ion movements once s.s. has been achieved:although few open Na+, Na+ larger e-chemical force acting upon it, that is, it is far <>> ↑ membr. permeability -->> ion species-->> ↑ contribution of ion species to membr. potential
Resting membrane potential =-70mV*
Goldman eqn: Vm=60log (PK[K]o+PNa[Na]o+PCl[Cl]i)/PK[K]i+PNa[Na]i+PCl[Cl]o)2.303RT/F=60Pion-->> relative permeability of ion
K+=1, Na+=0.035, Cl-=0.001 (more permeable to K+ because for K + channels found on those membranes <>
*neither Na+, nor K+=> Epotential, but r.m.p. is closer to K+ Epotential, because membr. more permeable to K+
K+ moves out through open leak K+ channels
inside cells becomes (-)K+flux has more import on r.m.p. than Na+ flux,
but Na+ (small no) channels also open in resting state
Na+move in cell, cancelling effect on equivalent no of K+ions simultaneously moving out.
there is a NET movement <>
Over time, [ ] of intracellular Na+, K+ ions does not change because Na+K+ATPase pump maintains&helps to establish [Na+, K+] gradients @ stable lvls, as they move 3Na+ out & 2K+ in.
This unequal transfer contributes directly to membr. potential.
Note: In a resting cell, the no of ions that move in the opposite direction through membr. channels down their [ ] and/or elec. gradients. As long as the [ ] gradients remain stable and ion permeabilities of the plasma membr. do not change, elec. potential across the resting membr. will also remain constant.
Excitable cell
Neurones, muscle cells, grandular tissue, fertilised eggs, plant cells-->>RMP
Express correct ion channels: VOLTAGE GATED ION CHANNELS
Nerst eqn: E=60logCo/Ci (mV)
Eq.pot. for a particular ion, [ion] out/in, 60: constant taking into account: R, T, valance of ion, Faraday elec. constant
If [ ] changes =>E changes
E for K+ ~-80mV, Na+ ~ +60mV
Ion movements once s.s. has been achieved:although few open Na+, Na+ larger e-chemical force acting upon it, that is, it is far <>> ↑ membr. permeability -->> ion species-->> ↑ contribution of ion species to membr. potential
Resting membrane potential =-70mV*
Goldman eqn: Vm=60log (PK[K]o+PNa[Na]o+PCl[Cl]i)/PK[K]i+PNa[Na]i+PCl[Cl]o)2.303RT/F=60Pion-->> relative permeability of ion
K+=1, Na+=0.035, Cl-=0.001 (more permeable to K+ because for K + channels found on those membranes <>
*neither Na+, nor K+=> Epotential, but r.m.p. is closer to K+ Epotential, because membr. more permeable to K+
K+ moves out through open leak K+ channels
inside cells becomes (-)K+flux has more import on r.m.p. than Na+ flux,
but Na+ (small no) channels also open in resting state
Na+move in cell, cancelling effect on equivalent no of K+ions simultaneously moving out.
there is a NET movement <>
Over time, [ ] of intracellular Na+, K+ ions does not change because Na+K+ATPase pump maintains&helps to establish [Na+, K+] gradients @ stable lvls, as they move 3Na+ out & 2K+ in.
This unequal transfer contributes directly to membr. potential.
Note: In a resting cell, the no of ions that move in the opposite direction through membr. channels down their [ ] and/or elec. gradients. As long as the [ ] gradients remain stable and ion permeabilities of the plasma membr. do not change, elec. potential across the resting membr. will also remain constant.
Excitable cell
Neurones, muscle cells, grandular tissue, fertilised eggs, plant cells-->>RMP
Express correct ion channels: VOLTAGE GATED ION CHANNELS
Different types of ion channels (sensory system: mechanosensitive ion channes, phosphorylation sensitive ion channels, poring for H2O channels. 2 of the most characteristics:)
- Ligand-gated ion channels: (e.g. ACh Receptor) change from close to open, protein shape change to open
- Voltage-gated ion channels: passive down elec.gradient, rapid, important for signalling in nervous system, cation channels, relatively selective for: K+, Na+, Ca++(40/40-12/12dif.channels)/ anion channels: realtively selective for Cl-
proteins exist in open, inactivated, closed states depending on membrane depolarization.
change in charge induces change!
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