PHYL3001 Lecture Notes - Lecture 1: Relative Permittivity, Chemical Potential, Nernst Equation
LECTURE ONE: Basic Concepts in Single Cell Electrophysiology
Lipid Bilayer and Membrane Permeability:
• Made up of phospholipid bilayer
• Polar region facing outside, hydrophobic region facing inside
• Regulates contents and movement of substances into/out of cells
• Selectively permeable
• Accepts small hydrophobic molecules and small uncharged polar
molecules
• ~ 10nm thick
• Transmembrane proteins → allows solutes to cross cell membranes
• Different transport mechanisms
o Passive transport → channel or transporter mediated
o Active transport
o Coupled transport → symports and antiports
Ion Channels:
• Leakage channels
o Always open
o Allow passive movement of ions
o Generally selective
o Set up resting membrane potential
• Gated ion channels → allow rapid diffusion of ions across membrane
o Voltage-gated → open due to change in electrical activity
o Ligand-gated → activated through binding to a ligand
o Stretch-activated → activated through physical transformation of
membrane
• Movement of ions → charge
• Channels are open for variable amounts of time
• Amount of channels open is random
• Ion channels have fixed amplitude
Ion Channels and Membrane Potentials:
• Membrane potential → major force on ions and molecules on all cells
• Osmotic balance in cells → ions are most abundant in dissolved solutes
• Ion flows and voltages can control fluid flows in specialized epithelia →
secretion and absorption
• Ion flows and voltages control many other phenomena
o Sensory signaling
o Forge generation → role of Ca2+
o Intracellular enzyme cascades
o Gene expression, cell growth and cell death
Establishing a Membrane Potential:
• Trapped organic anions
• Na/K pump → Na/K concentration gradients → net electrical negativity
• Cell membrane preferentially permeable to K
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