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 ~