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Neural Signaling: The Membrane Potential. Lesson 9. Membrane Structure. Barrier Compartmentalization Semipermeable selectively leaky Fluid Mosaic Model Phospholipids Proteins ~. Phospholipid Bilayer. Hydrophilic heads  (phosphate) Hydrophobic tails  (lipid). Membrane Proteins.

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membrane structure
Membrane Structure
  • Barrier
    • Compartmentalization
  • Semipermeable
    • selectively leaky
  • Fluid Mosaic Model
    • Phospholipids
    • Proteins ~
slide3

Phospholipid Bilayer

Hydrophilic heads 

(phosphate)

Hydrophobic tails 

(lipid)

membrane proteins
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 proteins ionophores
Membrane Proteins: Ionophores
  • Ion Channels
  • Non-gated
    • always open
  • Gated
    • chemically-gated
    • electrically-gated
    • mechanically-gated ~
chemically gated channels
Chemically-Gated Channels
  • ligand-gated
  • Ionotropic
    • receptor protein = channel
    • direct control ---> fast
  • Metabotropic
    • second messenger system
    • indirect ---> slow ~
membrane proteins1
Membrane Proteins

OUTSIDE

INSIDE

metabolic pumps active transport
Metabolic pumps: Active Transport
  • Membrane proteins
  • Pump ions
    • require energy
    • Na+ - K+
    • Ca++ (calcium)
  • Also various molecules
    • nutrients
    • neurotransmitters ~
biolelectric potential
Biolelectric Potential
  • Communication within neuron
    • electrical signal
  • electric current = movement of electrons
  • Bioelectric: movement of ions ~
ion distribution
Ion Distribution
  • Particles / molecules
    • electrically charged
  • Anions
    • negatively charged
  • Cations
    • positively charged ~
ion distribution1
Ion Distribution
  • Anions (-)
    • Large intracellular proteins
    • Chloride ions Cl-
  • Cations (+)
    • Sodium Na+
    • Potassium K+ ~
resting membrane potential

Cl-

Na+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

K+

+

+

+

+

+

+

+

+

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

K+

Cl-

Na+

Resting Membrane Potential

outside

Membrane

A-

inside

membrane is polarized
Membrane is polarized
  • more negative particles in than out
  • Bioelectric Potential
    • like a battery
    • Potential for ion movement
      • current ~
slide14

Bioelectric Potential

POS

NEG

OUTSIDE

INSIDE

forces that move ions
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 ~
equilibrium potential
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 ~
equilibrium potential1
Equilibrium Potential
  • R = gas constant
  • F = Faraday constant
  • T = temperature (K)
  • Z = valence (charge) of ion ~
equilibrium potential2

K+: z = +1

Cl-: z = -1

Mg++: z = +2

Equilibrium Potential
equilibrium potential3
Equilibrium Potential
  • Constants never change
  • Assume 25 oC (298 oK)
  • Use log10 ~
membrane potential
Membrane Potential
  • Net bioelectric potential
    • for all ions
    • units = millivolts (mV)
  • Balance of both gradients
    • concentration & electrostatic
  • Vm = -65 mV
    • given by Goldman equation ~
membrane potential goldman equation
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 ~
slide23

Organic anions -

Membrane impermeable

Opposing electrical force not required

Vm = -65 mV

A-

C

chloride ion
Chloride ion

Cl-

C

  • Concentration gradient equal to electrostatic gradient.
  • Leaks out neuron
  • ECl- = - 65 mV ~

Vm = -65 mV

E

slide25

Potassium ion

E

  • Concentration gradient greater than electrostatic gradient.
  • Leaks out neuron
  • EK = - 75 mV ~

Vm = -65 mV

K+

C

slide26

Na+

Sodium ion

C

E

  • Concentration gradientandelectrostatic gradient into neuron.
  • ENa+ = +55 mV ~

Vm = -65 mV

metabolic pumps
Metabolic Pumps
  • Active Transport mechanisms
    • Require energy
  • Move materials against gradient
    • Na+ - K+
    • Calcium - Ca++
    • Nutrients, etc.~
na k pump
Na+ - K+ Pump
  • Moves ions against gradients
    • Pumps 3 Na+ out of cell
    • 2 K+ into cell
  • Maintains gradients at rest
    • no active role in signalling
    • Energy = ATP ~
slide29

Na+

Na+

Na+

K+

K+

Inside

Outside

Na+

Na+

Na+

K+

K+

ATP

slide30

Na+

Na+

Na+

Inside

Outside

K+

K+

K+

K+