~BN09 membrane potential.ppt
Transcript of ~BN09 membrane potential.ppt
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Neural Signaling:The Membrane
PotentialLecture 9
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Membrane Structure
Barrier Compartmentalization
Semipermeable selectively leaky
Fluid Mosaic Model Phospholipids Proteins ~
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Phospholipid Bilayer
Hydrophilic heads
(phosphate)
Hydrophobic tails (lipid)
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Membrane Proteins
Channels Pumps
active transport Receptor protein sites
bind messenger molecules Transducer proteins:
2d messenger systems Structural proteins
form junctions with other neurons ~
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Membrane Proteins: Ionophores
Ions Channels Nongated
always open Gated
chemically-gated electrically-gated mechanically-gated ~
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Chemically-Gated Channels
ligand-gated Ionotropic
receptor protein = channel direct control ---> fast
Metabotropic second messenger system indirect ---> slow ~
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Membrane Proteins
OUTSIDE
INSIDE
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Metabolic pumps
Membrane proteins Pump ions
require energy Na+ - K+ Ca++ (calcium)
Also various molecules nutrients neurotransmitters ~
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Biolelectric Potential
Communication within neuron electrical signal
electric current = movement of electrons
Bioelectric: movement of ions ~
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Ion Distribution
Particles / molecules electrically charged
Anions negatively charged
Cations positively charged ~
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Anions (-) Large intracellular proteins Chloride ions Cl-
Cations (+) Sodium Na+ Potassium K+ ~
Ion Distribution
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Resting Membrane Potential
Membrane
outside
inside
Na+
Na+
Cl-
Cl-K+
K+
A-
+ + + + + + + + + + +
-----------
+ + + + + + + + + + +
-----------
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more negative particles in than out Bioelectric Potential
like a battery Potential for ion movement
• current ~
Membrane is polarized
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INSIDE
POS
NEG
Bioelectric Potential
OUTSIDE
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Forces That Move Ions
Concentration (C) particles in fluid move from area of
high to area of low concentration diffusion, random movement
Electrostatic (E) ions = charged particles like charges repel opposite charges attract ~
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Equilibrium Potential
Also called reversal potential Distribution of single ion across
membrane e.g., EK+, ENa+, ECl-
Potential for movement of ion if channel opens units millivolts (mV) Potential outside = 0, by convention ~
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Equilibrium Potential
R = gas constant F = Faraday constant T = temperature (K) Z = valence (charge) of ion ~
i
o
K K
K
ZF
RTE
][
][log
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Equilibrium Potential
i
o
K K
K
Z
mVE
][
][log
58
K+: z = +1
Cl-: z = -1
Mg++: z = +2
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Equilibrium Potential
Constants never change Assume 25 oC Use log10 ~
mVmVEK
75400
20log58
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Equilibrium Potential
mVmVENa
5550
440log58
10
i
o
Na Na
Na
ZF
RTE
][
][log
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Membrane Potential
Net bioelectric potential for all ions units = millivolts (mV)
Balance of both gradients concentration & electrostatic
Vm = -65 mV given by Goldman equation ~
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icliNaiK
ocloNaoK
m ClPNaPKP
ClPNaPKP
F
RTV
][][][
][][][log
Membrane Potential: Goldman Equation
P = permeability at rest: PK: PNa: PCl = 1.0 : 0.04 : 0.45
Net potential movement for all ions known Vm:Can predict direction of movement of any ion ~
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C
Organic anions - Membrane impermeableOpposing electrical force not required
A-
Vm = -65 mV
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Chloride ion
C
E
Cl-
Vm = -65 mV
Concentration gradient equal to electrostatic gradient.
Leaks out neuron ECl- = - 65 mV ~
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K+ C
EVm = -65 mV
Potassium ion
Concentration gradient greater than electrostatic gradient.
Leaks out neuron EK = - 75 mV ~
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Sodium ion
Na+
C EVm = -65 mV
Concentration gradient and electrostatic gradient into neuron.
ENa+ = +55 mV ~
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Metabolic Pumps
Active Transport mechanisms Require energy
Move materials against gradient Na+ - K+ Calcium - Ca++ Nutrients, etc.~
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Na+ - K+ Pump
Maintains gradients at rest Pumps 3 Na+ out of cell 2 K+ into cell Energy = ATP ~
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Inside Outside
Na+
Na+
Na+
K+
K+K+K+
Na+
Na+
Na+
ATP
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Inside Outside
Na+ Na
+Na+
K+
K+
K+
K+