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Neural Signaling: The Membrane Potential Lesson 8.
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Transcript of Neural Signaling: The Membrane Potential Lesson 8.
Neural Signaling:The Membrane Potential
Lesson 8
Membrane Structure
Barrier Compartmentalization
Semipermeable selectively leaky
Fluid Mosaic Model Phospholipids Proteins ~
Phospholipid Bilayer
Hydrophilic heads
(phosphate) Hydrophobic
tails (lipid)
Membrane Proteins Channels Pumps
active transport Receptor protein sites
bind messenger molecules Transducer proteins:
2d messenger systems Structural proteins
form junctions with other neurons ~
Membrane ProteinsOUTSIDE
INSIDE
Metabolic pumps: Active Transport
Membrane proteins Pump ions
require energy Na+ - K+ Ca++ (calcium)
Also various molecules nutrients neurotransmitters ~
Biolelectric Potential
Communication within neuron electrical signal
Electric current = movement of electrons Bioelectric: movement of ions ~
Ion Distribution
Particles / molecules electrically charged
Anions negatively charged
Cations positively charged ~
Resting Membrane Potential
Membrane
outside
inside
Na+
Na+
Cl-
Cl-K+
K+
A-
+ + + + + + + + + + +
-----------
+ + + + + + + + + + +
-----------
Bioelectric PotentialOUTSIDE
INSIDE
POS
NEG
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 ~
Concentration gradient
HI Lo
HI Lo
Concentration gradient
HI Lo
Concentration gradient
Equilibrium
Na+ K+
like charges repel
Electrostatic gradient
Na+ A-
opposite
Electrostatic gradient
charges attract
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 ~
Membrane Potential
Net bioelectric potential for all ions units = millivolts (mV)
Balance of both gradients concentration & electrostatic
Em = -70 mV given by Goldman equation ~
C
Organic anions - Membrane impermeableOpposing electrical force not required
A-
Em = -70 mV
Chloride ion
ECl- = - 70 mV Concentration gradient equal to electrostatic gradient. No net movement at resting potential ~
C
E
Cl-
Em = -70 mV
K+ C
EEm = - 70 mV
Potassium ion
EK = - 90 mV Concentration gradient greater than
electrostatic gradient. Leaks out neuron ~
Sodium ion
Em = - 70 mV
ENa+ = +50 mV Concentration gradient and
electrostatic gradient into neuron. ~
Na+
C E
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 ~