Nerve and muscle signalling © Dr Bill Phillips 2002, Dept of Physiology Rm N348 Anderson Stuart Bldg

Nerve and muscle signalling Lectures Membrane ionic gradients (Lect 1) Membrane Potential (Lect 2) Action Potential (Lect 3) Action potential propagation (Lect 4) Synaptic Transmission (Lecture 5)

Lect. 1 Membrane ionic gradients Dr Bill Phillips Cells and cell compartments Fluid mosaic model of our membranes Concentration gradients and diffusion Selective permeability and osmosis Membrane channels and transporter

Plasma membrane: Lipid bilayer Bipolar phospholipids Hydrophilic head groups (face water) Long hydrophobic tails (oily interaction) Self assembling, stable Barrier to large, charged, polar molecules

Plasma membrane- Fluid mosaic Lipid bilayer is modified by addition of: Transmembrane proteins (eg channels, transporters, receptors) Membrane-attached proteins (eg cytoskeleton-linking proteins) Specialised lipids & glycolipids Channels and transporters selectively modify permeability of membrane

Membrane transport For substances that cannot diffuse across the lipid bilayer there are: Active transport- membrane proteins that use energy to force substance UP its concentration gradient Facilitated Diffusion-facilitate a substance diffusing across the membrane molecule by molecule Diffusion channels eg water channels and ion channels

Active transport Primary active transporter proteins use energy of ATP to force molecules or ions UP their concentration gradient Secondary active transporter proteins use the diffusion energy of pre-exising concentration gradients to drive a second substance UP its concentration gradient

Primary Active transport example- Na + /K + Pump In healthy cells the cytoplasmic concentration of K + is high (~120mM) while the concentration of Na + is low (~10mM) The Na + /K + Pump (aka Na + /K + ATPase) is responsible for maintaing this concentration gradient over a time frame of minutes to hours

Facilitated diffusion- summary Involves a membrane protein that can shepherd a large/polar/charged molecule across the lipid bilayer Work is done in changes to conformation of the transporter protein Facilitated diffusion is driven by the chemical driving force acting on the substance

Membrane ionic gradients: Revision Cells and cell compartments Fluid mosaic model of our membranes Concentration gradients and diffusion Selective permeability and osmosis Membrane channels and transporters