neural signaling: the membrane potential lesson 8
TRANSCRIPT
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Neural Signaling:The Membrane Potential
Lesson 8
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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 ProteinsOUTSIDE
INSIDE
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Metabolic pumps: Active Transport
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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Resting Membrane Potential
Membrane
outside
inside
Na+
Na+
Cl-
Cl-K+
K+
A-
+ + + + + + + + + + +
-----------
+ + + + + + + + + + +
-----------
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Bioelectric PotentialOUTSIDE
INSIDE
POS
NEG
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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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Concentration gradient
HI Lo
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HI Lo
Concentration gradient
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HI Lo
Concentration gradient
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Equilibrium
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Na+ K+
like charges repel
Electrostatic gradient
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Na+ A-
opposite
Electrostatic gradient
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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Membrane Potential
Net bioelectric potential for all ions units = millivolts (mV)
Balance of both gradients concentration & electrostatic
Em = -70 mV given by Goldman equation ~
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C
Organic anions - Membrane impermeableOpposing electrical force not required
A-
Em = -70 mV
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Chloride ion
ECl- = - 70 mV Concentration gradient equal to electrostatic gradient. No net movement at resting potential ~
C
E
Cl-
Em = -70 mV
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K+ C
EEm = - 70 mV
Potassium ion
EK = - 90 mV Concentration gradient greater than
electrostatic gradient. Leaks out neuron ~
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Sodium ion
Em = - 70 mV
ENa+ = +50 mV Concentration gradient and
electrostatic gradient into neuron. ~
Na+
C E
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Na+ - K+ Pump
Moves ions against gradients Pumps 3 Na+ out of cell 2 K+ into cell
Maintains gradients at rest no active roll in signalling Energy = ATP ~